# Light Meter Benchmark Testing – CPF style



## SilverFox (Oct 3, 2005)

Light Meter Benchmark Testing – CPF style 10/2/05

Have you ever wondered about the accuracy of your light meter?

Have you ever wondered why someone else seems to report higher (or lower) lux values than you observe, even when you are measuring the same type of light?

What if we could take one light and have everyone measure the lux at 1 meter or foot candles at 1 foot and log in their findings?

I want to open this topic up for discussion. Please understand that there are no “right” answers. You measure what your light meter says and report it here. All I am trying to do is level the playing field by providing stable light sources for the comparison.

All discussion will be conducted in this thread. The pass around thread will only contain those who want to participate. *Discuss the method and report the findings here in this thread.*

Don (McGizmo) will provide an Aleph light based on the NextGen driver running a Lux III LED at 500 mA. He also will be providing a beam shaper that can be used for another *optional* measurement if you want to do that. In addition, Don will be sending another head along that has a blue K2 LED in it. It will fit the same battery holder as the LUX III.

*Note:* After the first round of testing by Don and some additional testing by me, Don is adding Red and Green LED lights to the package. This will give us three points of the spectrum (red, green and blue) as well as white LED and an incandescent.

PK of SureFire will be providing an A2 without LED’s for this testing.

These three lights will become the CPF light standards. They will be used only for testing. We are trying to conserve the LED and Lamp life.

*To participate in this round robin testing:*

1. - You will need to have a light meter (be sure to check the battery).

2. - You will need to have an accurate way to measure 1 meter (which is 39 3/8”). If you measure and report in foot candles, your measurement should be taken at 1 foot. If your meter measures both lux and foot candles, I will leave it up to you to decide if you want to report both.

3. - You will need to have three (3) fresh primary CR123A batteries (any brand is OK) one for the Aleph and two for the A2 – *NO RECHARGEABLE CELLS* will be used during this testing. The LUX III will be tested first, then the blue K2 will be tested on the same battery.

*Note:* We have just added a red and green LED light to be tested. You should be able to test the white, blue, green, and red LED lights on one battery *(in that order)*, but if you find that it is taking a bit longer than you had planned, you can use the batteries from the A2 (after you have tested the A2 of course).

4. - You will need to take the measurements as you would normally do. We hope that you have a dark area that is as free from reflections as possible, but please report your findings as you would normally do the measurements. *No special set up is required.* You may do another set of measurements if you want to tidy things up and report that as well.

5 – You will be required to follow the “CPF Standard Procedure for Light Meter Measurements” listed below.

6 - You will need to post what your meter reads, along with the brand and model of meter. We will also need the room temperature during the measurements.

7. – You will need to contact the next person in line to make sure they are available to participate before sending the light to them.

8 - You will need to pay the postage and insurance required (the insurance value of these lights is $500, and we can call them benchmarking lamps) to send it to the next person and make sure it gets packaged securely and sent out.

At the end of the testing, the lights will be returned to me. I will store the lights at the end of the testing. They will be the CPF standard light sources. The will be available for future tests by arrangement. These “standards” will not be used for general illumination, but will be reserved only for testing purposes.

*CPF Standard Procedure for Light Meter Measurements*

1. - You can not alter, modify, or take apart these lights. Everything needs to be aligned and kept in alignment so we have a good basis for comparison. Opening the bezel could allow the reflector to shift and that would alter the following measurements.

2. - Your light meter will be set up with 1 meter distance for those measuring in lux (or 1 foot for those measuring in foot candles) between the dome of the meter sensor and the outside edge of the bezel ring, 

3. - Check the lens to make sure it is clean and free from fingerprints, and make sure the battery in your light meter is good.

4. - The lights will be turned on for a minimum of two minutes before taking measurements. This goes for all lights.

5. - You should take the measurements as you normally would and report what you get. You can then do another set of measurements under tighter control and report those measurements as well if you are so inclined to do so.

6. – You should take a minimum of three measurements to check the repeatability of your set up. This means taking your system apart and putting it back together each time. We are checking to see if you can repeat the same numbers each time you set up. Report your three readings so we can see how much scatter there is, then average them together for your overall number.

Schedule

Lets try to keep things moving along and make every effort to get the lights sent to the next person within 2 days. 

Please understand that these lights are intended for testing purposes only. They have a limited life time and should not be used for general illumination needs, or battery run time tests.

At the end of the pass around (or at the end of the US portion depending on what we can set up with the laboratory), the lights will be sent to a professional laboratory along with a copy of our “standard procedure.” Their results will allow us to “adjust” our readings as necessary to better reflect reality.

It should only take a few minutes to take your measurements, post them, contact the next person in line, and pack the light up to send off. I know that unexpected things come up but let's try to keep things going and make sure it gets sent to the next person within 2 days.

I think this will go real quick and believe it would be a great service to the CPF community.

*What do you think? Should I set it up?* It is in the works...

Tom

You can sign up for the pass around here.

Here is the list of people participating in this testing.

In the US
McGizmo - finished testing. Results posted here.
SilverFox - finished
The LED Museum - finished
Bwaites - finished
Sigman - finished
Bogus1 - finished
Evan9162 - finished
Chevrofreak - finished
Andrewwynn - finished
N162E - finished
Wptski - finished
JTR1962 - finished
Rdshores - Passed Away 12/31/05 - RIP
Quickbeam - finished
Jtice - finished
Kitelights - finished
4sevens - finished
Wquiles - finished
Cy - finished
Archangel - finished
Brock - finished but need meter model and serial number
Codeman - finished
Off to Lighting Science Inc for official certification - finished
Lildave - finished
Yaesumofo - finished
Gadget Lover - finished
Bullzeyebill - finished
Geroges80 - finished
NextLight
Robstarr-Lite

Tvodrd
HarryN - on hold until later
Modamag

NewBie - with a Minolta CS-1000
McGizmo

In Puerto Rico
Reima

In Canada
We did not have a lot of response from Canada, so Chimo who has a Meterman decided to pass on this round. I had suggested he send his meter to someone in the US so he could avoid the extra taxes and duties involved in shipping the test lights to Canada. Perhaps we can get the serial number of his Meterman to see where it fits in with the other meters...

In Europe
Kiessling
Mark2
Winny

In Argentina
PEU

Tom

The results are very interesting…







What is also interesting is looking at the standard deviation we are getting.







The official results from LSI are:
A2 Incandescent - 2508 lux
White LED - 1270 lux
Blue LED - 151 lux
Green LED - 2357 lux
Red LED - 2379 lux


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## evan9162 (Oct 3, 2005)

Awesome. I like the idea. We'll have a good standard of measurement for comparison. (and we can 'calibrate' our meters to the CPF gold standard Aleph)

One thing about the measurement technique: After turning on the light, the Lux will warm up a bit. Are we to take a measurement immediately, or is there some time we should wait for the light to reach thermal equilibrium?

I'd be interested simply to see how valid my piecewise lumen integration technique is.


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## CroMAGnet (Oct 3, 2005)

I'm in. Do you think that different battery brands will show different results. Like some of the runtime testing of say even the copper top Duracell and the Duracell Ultra. (IIRC) Would they have slightly different voltage output and skew the results?


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## Mark2 (Oct 3, 2005)

I'm in, great idea!


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## wptski (Oct 3, 2005)

Tom:

What would be the procedure for locating the light sensor in the head's beam or spot? Centered for highest reading, I assume?


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## Archangel (Oct 3, 2005)

Just want to throw out that "centered" and "highest reading" aren't always the same place.

And that i'm interested in getting in on this.




wptski said:


> What would be the procedure for locating the light sensor in the head's beam or spot? Centered for highest reading, I assume?


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## Roy (Oct 3, 2005)

Remember:

1 [email protected] = 1Cd(candella) = [email protected]


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## SilverFox (Oct 3, 2005)

Hello Evan,

Your are the other person I had in mind when I mentioned JTR, but I couldn't remember who you were. Thanks for jumping in here. I was going to do a search, but am not sure the search function is fully functional yet.

Don is going to send me a "new" light. I will run it for 4-5 hours to break it in before starting the testing. Does that seem about right?

My thought is to turn the light on and take the measurement after 1 minute of warm up. Does that sound OK?

Tom


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## lildave (Oct 3, 2005)

Great Idea !!! I'm in


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## SilverFox (Oct 3, 2005)

Hello CromagNet,

The NextGen driver will regulate the current to the LED so battery voltage does not really matter.

I discussed this at some length with Don and we decided that the type of battery will not matter for this test, as long as it has a high enough voltage to bring the light into regulation.

Total run time is a different test that is dependent on battery brand, but every battery I have seen has been able to handle 500 mA for at least a few minutes.

Tom


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## SilverFox (Oct 3, 2005)

Hello Bill,

Yes, we are looking for the highest reading. Some meters have a max hold or peak hold that makes that a bit easier to read.

Tom


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## SilverFox (Oct 3, 2005)

Hello Roy,

That is correct.

I have seen some light/reflector combinations that influence closer readings. I don't think it would be a problem with the Aleph 2, but in the interest of having everyone measure the same beam, I suggested taking a fc measurement at 1 yard and working backwards.

When I receive the light, I will do a measurement at 1 foot and see if there is any reason for concern. As you have pointed out, the fc measurement at 1 foot should equal the lux measurement taken at 1 meter.

Tom


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## evan9162 (Oct 3, 2005)

Tom,


4-5 hours wouldn't be a bad idea. 24 would be more thorough, but overkill in this case since it's got a good current regulator on board.

As for testing time, since (i'm assuming) you'll have first shot at this, why not during your break-in, set up your light meter and take measurements throughout the run - turn-on, 1 minute, 5 minutes, 20 minutes, 1 hour...Then maybe repeat the first 4 measurements after the 5 hour test to verify - then you'll know when the reading will level out, and how long the light will need to be turned on before getting a "good" reading. 

Maybe don can tell us about how long the aleph takes to reach thermal equilibrium and just use that value?

At 500mA, though, I can't see heating up making more than about a 5% difference. Good idea on using a relatively "low" powered light, it makes for a more stable source.


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## SilverFox (Oct 3, 2005)

Hello Evan,

Good ideas...

To break the light in, I also have the option to hook it up to my power supply and let it run for a day or two.

On the other hand, for our actual measurement, does the actual time really matter? If we are all taking the measurement at the same elapsed time, we should all be at the same thermal gradient level.

Tom


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## jtice (Oct 3, 2005)

This is an EXCELLENT idea !!!

I would gladly take a turn taking a measurement.

This has been a problem for a long time, 
everyones conditions are very different, and different meters will take a wide range of measurements.

One thing I have noticed,
my PEAK Lux readings are very different from what I can "peak" at manually.
On average, MY peak reading is higher than the meters peak reading.
Anyone else notice that?

Also, we are gonna have a problem here,
even though you are having everyone use a "fresh" cell,
they WILL be different, in both voltage, and resistance.
I am not sure how much that will effect the regulated Nexgen though.

[EDIT] eh, just reread some above posts.
Seems Don says the batteries shouldnt matter, as long as they are up to the proper voltage.
I hope that is true.

~John


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## bwaites (Oct 3, 2005)

I'm in.

This will complicate things, but what about an incandescent source for the test?

One of each type of light might be useful!

Bill


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## McGizmo (Oct 3, 2005)

Hi guys,

I have a UX1J on an E-screw currently runing on a bench supply at 500 mA to break in the LED. I'll let it run for over 24 hours straight before I build out the light engine. This should bring the die well into its lumen maintenance curve and the elapsed time used in the various meter tests shouldn't have a significant impact on the LED. I will measure it before sending to Tom and then I can re measure it upon its return. I have noticed that the NexGen converters seem to be rock steady in terms of current control and probably 10 converters set at 500 that I actually measured all showed 503 mA current actually going to the LED. This drive level on the LuxIII and especially with an efficient UX1J should not produce levels ot thermal output that would skew our readings, IMHO.

This is *not* a contest to see who can get the highest reading!!  The idea here is for all of us to get a sense of relative measures and how our meters and methods compare to other meters. It will also be interesting to see how much variation we see in measurements of the same light. YMMV is always at play and this will give us an idea of the degree to which YMMV based on presumably the same light source.

I was thinking a measure with the beam shaper as well as the reflector might give us more data as the beam shapper provides a more homogeneous distribution of light and the lux varies much less across the beam. It also gives us two output levels to measure and report.

*EDIT: This light will belong to CPF and it should be available for future tests and measurements if there is a "keeper" of the light willing to take on the responsibility (Tom??? ) It might also be worth considering having this light measured by a professional firm for both lux as well as flux. :shrug: *


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## evan9162 (Oct 3, 2005)

You're probably right, it probably won't make too much of a difference. 

[rambling]
Though the environment can make a difference. You will see a 5% difference, if say, I do the measurements in my garage at 10C, and someone else does their measurements in the house at 25C. Or, if someone does measurements in their garage in winter at 10C, then 6 months later (shouldn't take that long, but just an example), it gets to someone who tests in their garage where it's 30C, then you could see a 7% difference. 
You get 5% difference for every 15C difference in junction temp, which also means you get 5% difference for every 15C difference in ambient temp.

[/rambling]

I'm probably just being too picky in thinking about controlling for every variable we can and just having the light meter be the variable under test.

It'd probably be a good thing to describe the test environment, then we can sort of control for that after the fact.

So, after all that, measuring at 1 minute sounds good to me :thumbsup:


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## jtice (Oct 3, 2005)

The Beam shaper is a very good idea Don,
REAL good idea actually.

I think everyone that has a meter that can do Peak readings, 
should take one with the peak set to on, AND a reading seeing what peak they can get manually.

And yes, each person should describe their test environment also.
Along with what meter they have of corse.

~John


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## McGizmo (Oct 3, 2005)

For an incandescent source, it should be a SF A2 where we have voltage regulation, yes? Perhaps one with the LED ring removed as the LED's are a function of Vin.

*EDIT: I will be installing a single stage switch on this light so you will only have regulated high to measure. THe resistored low is a function of the battery and not likely something we should consider "controlled". 

I would also like to point out that the variations of measure due to ambient conditions are at play every time someone reports a meter reading and it is most important for the measurer to be consistant in their method and environment; not only in measuring this light but in other measures given on other lights. :shrug: *


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## TomBrown (Oct 3, 2005)

I think this is a great project, although I don't intend to participate.

If you're worried about light fluctuations, why not just make Tom the first and last tester on the list? It might be interesting to verify the process, anyway.


... just 2 cents from the peanut gallery.


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## jtice (Oct 3, 2005)

ah, the addition of an incandecent will be nice also.

yes, making your test environment the same each time is very important.
When I started dogin runtime tests, I sat down and thought it out.
I have my computer screens, and one small CCFL light on so I can see to move around the room.
That is the same EACH runtime I do.
And, I Zero out the meter at the start of each test, 
so, the 3 to 4 lux I get from that CCFL is not in the reading.

I have noticed that my setup varies by NO MORE than 2 lux under any circumstance,
2 Lux is good enough for me 

~John


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## SilverFox (Oct 3, 2005)

Hello John,

I believe the reason that Peak readings are sometimes a bit higher is because of the sampling rate.

My meter (Extech EA30) has a bar graph, digital numbers, and a peak or max hold. The bar graph samples at 13.3 times per second, the digital display at 1.3 times per second, and the peak hold can capture peaks down to 100 micro seconds.

I find that if I mount the light in a tripod and gradually move to find the highest reading, I can duplicate the peak readings. I can not do this holding the light in my hand.

Tom


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## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



SilverFox said:


> I would guess that JTR (and others) would like to take their own lumen measurements in addition to the lux measurements.


Yes, I'm interested but I have two points here. First, I'm not really set up to do lumen measurements with flashlights because of the very narrow beam angle relative to bare LEDs and also the necessity of making a custom test jig to hold the flashlight. Therefore, it would be a lux only test unless I can think of a quick way to make a test jig for the flashlight in question. Even so, I still wouldn't put too much stock in the accuracy of the results given that my methodology is really more geared towards bare LEDs. I might need to take readings every 1° for the first 10° or 20° instead of every 5°.

Second and more important, as strange as it may seem I *don't* have any CR123A batteries so I might be out for that reason. I only own one light which uses them, namely a Streamlight Tasklight 2-L given to me by one of the members here for some work I performed. If not for this gift I wouldn't have any because as everyone knows I avoid disposables and lights that use them like the plague. Anyway, my Streamlight has been sitting useless for a few months for want of batteries because I'm waiting for rechargeable lithiums better than what is currently available. I do have loads of AA NiMH and I'm sure everyone else here has at least a few so is there any chance of doing this test with a light which uses them? That makes doing things like a warm-up period much more feasible since you have an essentially unlimited supply of power, and also NiMH have less voltage sag than lithiums (more consistency from person to person). Doesn't the Aleph have a tube which lets it take AAs?


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## SilverFox (Oct 3, 2005)

Hello Bill,

What do you think of Don's suggestion of an A2?

Tom


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## SilverFox (Oct 3, 2005)

Hello Don,

Chris at Sphere Optics mentioned that he might be able to do a sample for us at a greatly reduced price (maybe free). Perhaps we could include him on the list...

Tom


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## Roy (Oct 3, 2005)

Who is going to hold the standard light meter set-up? If I measure (say) 10 LUX on my light meter set-up, to what/whose standard am I compairing it to?


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## cy (Oct 3, 2005)

Silver, excellent idea!!! and thanks for doing this. I'm in..

have thought this needed to be done for some time. 

wondered about consistancy of Lux readings from meter to meter from way back.

was part of group buy for Meterman awhile back. would be nice to see other people from same group buy on this test. 

many thanks to Don for providing a calibration standard with his sphere/aleph. 

have always felt Fluke measurements are accepted as accurate due to tracebility. hopefully this will prove or disprove accuracy of light meters we are using.


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## js (Oct 3, 2005)

Tom (and Don),

Excellent idea. I thank you for your efforts on this. I beleive that it will be very enlightening.


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## Brock (Oct 3, 2005)

Count me in as well.

We could do both, the Aleph and the A2 to see what we get, can't hurt. If someone could keep this all in excel it would be easier to look at. I would do it, but I am swamped here and check in about every other day.


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## chimo (Oct 3, 2005)

*If* this does a northern loop (Canada), I would love to be included. Great idea!

Paul


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## Bogus1 (Oct 3, 2005)

I'd be interested in participating. I only have a meterman LM631, but I am very careful with my tests and they are consistent on my end. However I have sold lights to buyers that have claimed the lights I sold them tested 50% higher on their meters.

jtice, the peakhold on my meter is useless IMO and I just catch the highest reading visually.

The beam shaper is a good idea because it will perhaps average out the light to reduce discrepencies in our methodology. However I would state that at 1 meter I find narrower hot spots from the A1 or A3 are much easier for consistently finding the highest reading. A wider spot, as on an A2, requires more searching and perhaps some of us will be reading from a different portion of the spot.

Also, for me it might take up to a minute to find the highest reading, so I would start looking immediately after turning on the light and then take the reading at 1 minute.


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## SilverFox (Oct 3, 2005)

Hello Roy,

The goal of this project is to see how much variation there is in the light meters we are using.

At first, I was thinking that Don's new integration sphere set up would be the "yardstick" that we would be measuring to, but it seems he is wimping out on that idea... :nana: He suggested sending the light(s) to a professional lab and using their results as the official yardstick.

This sounds good to me (and takes the monkey off of Don's back), but if we can not pull a favor or two, we may have to take up a small collection to pay for this.

Tom


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## SilverFox (Oct 3, 2005)

The only issue I can see with using an A2 is that the LED's may introduce a variable.

Does someone have an A2 without LED's that they would like to donate to this cause?

Another suggestion may be the Pelican M6. Bill has offered to donate one of those as he has several. I am not up on the regulation of the M6. We may have to dig up some information on it.

Tom


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## chevrofreak (Oct 3, 2005)

Yeah I'm definately interested. I ran my light meter on a 9v transformer and its as if the solar cell became more efficient. It still reads zero properly but lately lux readings seem to be about 10% higher than they should be. I hope my meter isnt damaged......

I'd be able to use the light to measure off a distance that gives me the exact reading everyone else is getting, and that should allow me to compensate.


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## The_LED_Museum (Oct 3, 2005)

I have a Meterman LM631 light meter that can measure in lux, but I do not have the capability to measure distances in meters, so I'll have to pass on this one. :shakehead:


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## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

I was just brainstorming while showering and came up with a few ideas:

1) Instead of batteries, let's rig the light up to run off of a power supply. All you have to do is solder two wires to where the battery + and - terminals would go, and connect those wires to a jack. An ideal power supply for this light is here, and a matching jack is here. The supply is the same one I used with my LaCrosse charger. It produces 3.3 volts at 4.55 amps maximum. 3.3 volts more or less matches what a fresh 123 cell will produce. A standard power supply which is shipped with the light eliminates one variable, namely the difference in batteries, from the equation. It also allows those of us without 123 cells to participate. 

2) Warm up the light until it reaches thermal equilibrium (no further change in lux readings). My guess is this will take no more than 30 minutes. Once someone determines the time needed to reach thermal equilibirium (this needs to be done _before_ the light makes the rounds for testing), then we can require a warmup of x minutes before testing. One minute seems too short. Also, from my experience trying to find the hot spot of lights you'll often be jiggling the light around for somewhat longer than that. The net result would be inconsistency from person to person. A standard warm-up time to thermal equilibrium eliminates this variable.

3) The only important variable remaining is temperature. Since I can't expect everyone to provide the same exact standard environment what we can do is simply note the ambient temperature during testing, and apply the relevant lux corrections in an Excel spreadsheet based on Lumiled's graphs of white LED output versus temperature.

4) Some sort of seal or something which can provide evidence of tampering on the bezel might be a good idea. I don't expect that anyone testing will intentionally take the bezel apart, but I'd prefer an easy way to confirm that the light hasn't been tampered with, perhaps due to a customs inspection if it crosses borders.

Any thoughts or additions on these ideas?


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## McGizmo (Oct 3, 2005)

Hi guys,

I believe I have a Balrog 3x123 tube that could be used for 2xAA on the head as an alternate to the 1x123 pak. The NexGen should be fine with this and provide the same light output. However, I would rather provide those who do not have CR123 batteries with a battery instead of donating this tube to the cause and confusion. At $1.25, I don't think this is an unsurmountable issue!  I can try to come up with an A2 as well and I'll bug my buddy the major weenie on this issue. It is a simple proposition of removing the LED ring and I think any DD incan is too prone to variables of batteries to be of service.

Bogus has brought up a point worthy of consideration and I could supply an Aleph 1 head instead of the Aleph 2 if we agree that this is a better test light?!?!?! I can still mount this light to my IS which is something I want to do. I will report my flux readings but since I don't know how close to callibration my system is, it is a number to take with some salt. I would like to know how my flux measure compares with a *real* one, for that matter!

I would also hope that the CPF reviewers partake in this and add their findings to the data base.


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## bwaites (Oct 3, 2005)

The ONLY commonly available production light that is regulated is the Surefire A2. The Pelican M6 is not regulated.

However, the LED's of the A2 are not regulated, and if they are on, especially at just one meter, they themselves introduce a variable. 

The only way to make this work would be to pull the ring of LED's and I'm not sure the main bulb works if you do that. I've never tried it with the LED's removed.

While this test would best be done with a regulated incan, the only way to do that, with the A2, might be undoable. 

Does anyone have an A2 that they have pulled the LED's on and then run to see if it works?

The Pelican M6, while not regulated, is a known quantity. Unfortunately, the state of the cell will play some part in the readings. There would be no way to take all the variables out. 

Don and I cross posted saying essentially the same thing.

Bill


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## McGizmo (Oct 3, 2005)

:thinking:

jtr, I really don't think CR123's are that difficult to come up with, are they? I will do a runtime test on the test light prior to sending it off to Tom but I do not believe a half hour is required for warm up time!!! 

If you consider the following runtime graph, what difference do you see after a few minutes, compared to say 30 minutes:







I can also check the NexGen converter prior to assembly and vary the Vin and note the I-out.


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## McGizmo (Oct 3, 2005)

Shall we set the measurment distance to 39" for those metrically impaired?


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## Roy (Oct 3, 2005)

McGizmo said:


> Shall we set the measurment distance to 39" for those metrically impaired?



..or one foot for those of us whose light meters read in Fc! If the distances are kept at one foot for Fc and one meter of LUX, then we should be able to move back and forth between [email protected] = [email protected]


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## SilverFox (Oct 3, 2005)

Hello Don,

I have a Stanley metric tape measure that I would be glad to throw in the box to maintain consistency.

Tom


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## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



McGizmo said:


> jtr, I really don't think CR123's are that difficult to come up with, are they.


You may be right, but I think using _any_ batteries here, whether NiMH AAs or CR123s, is going to introduce an unwanted variable. While the light may be technically regulated, in my testing I've noticed that the LED current varies by as much as 10% with certain regulators with the kind of changes in voltage which will occur when running off of a battery. That's why I suggested the power supply idea. We simply have no way of knowing if one set of batteries will produce the exact same drive current as another, and as a result we won't know if differences in the results are due to differences in the light meters or differing LED drive currents. I'm thinking of ways to do the test in such a manner as to eliminate all variables except temperature so that the results really are due solely to the differences in the light meters. Remember that I suspect our results will not differ by much more than 5%, perhaps less, perhaps a little more. Minor variations in LED current due to different batteries will most certainly be a confounding factor in this case.


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## evan9162 (Oct 3, 2005)

Don,

Drawing a straight line from the 3900 lux mark, after 30 minutes, the light is putting out just over 3900 lux, a difference of about 2% from the 4000 lux it produces for the first few minutes.


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## evan9162 (Oct 3, 2005)

Roy said:


> ..or one foot for those of us whose light meters read in Fc! If the distances are kept at one foot for Fc and one meter of LUX, then we should be able to move back and forth between [email protected] = [email protected]




They won't necessarily be equal. Since we're dealing with a light source that's quite large (reflector), the closer you get the more the relationships between the measurements fall apart. This is due to the fact that at 1 foot, the beam hasn't had enough distance to converge the same as it would at 1 meter. I would say that your readings at 1 foot, after being converted, would be significantly lower than the rest of the group.

For a lot of testing, I actually do measurements at 2 meters then multiply by 4. A lot of the time, especially with larger reflectors like a Mag reflector, I find that multiplying a 2 meter reading by 4 results in a slightly higher 1-meter-equivalent lux reading than actually measuring at 1 meter - beam convergence has a lot to do with this.


----------



## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



evan9162 said:


> Don,
> 
> Drawing a straight line from the 3900 lux mark, after 30 minutes, the light is putting out just over 3900 lux, a difference of about 2% from the 4000 lux it produces for the first few minutes.


I'll also add that we don't know if that 2% is because the LED gets hotter, or because the LED current changes as the battery runs down. It could be that the LED gets hot enough to change in output by, say, 5% after 30 minutes, but the regulator feeds it 3% more current when the battery is near the end of life so that we only end up with a 2% difference in output. Some regulators feed more current as the battery runs down, some less. It depends on design. Current regulation in general isn't as precise or as consistent as voltage regulation for a bunch of technical reasons, most having to do with feedback loop stability.


----------



## andrewwynn (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

this is a grand idea.. i've always been wondering about readings here and there and if i'm doing mine correctly etc.. i have noticed at least one time when somebody posted an 'unrealistic' lux reading they had been measuring near a wall and the light reflected off the wall and gave an erroneous reading since the wall acted like a reflector of course. All you need to do for the accurate meter measurement is include a string with a weight on one side and a knot in it at 1m.. make it a little longer so you can hold it and measure to the mark. 

I use a 'corner' of a wall (door jamb) to do my measurements.. avoids the bounce-back problem since the light bounces away from the sensor, and i have a mark on the wall at 1m.. people need to be aware if their meter (as mine) measures from the top of the dome when it comes to distance.. makes a difference of 1" which will make a pretty big difference in lux reading when measuring high-output. 

count me in. 

-awr


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## Kiessling (Oct 3, 2005)

Great idea !!! :thumbsup:
I am IN of course ... and I can even measure in metric scale :nana:

It seems that the NG is sufficiently stable when thinking in pragmatic terms, but Don could always do a runtime test and calculate the variations in lux over the runtime. Drive current isn't important here IMHO as all we measure is lux, and lux it is that we want to compare and calibrate to, not current. So ... if the lux readings are consistent over time I don't care about current. Or did I miss something and look stupid now? 

bernie


----------



## winny (Oct 3, 2005)

Great idea! :thumbsup: 

Count me in.


----------



## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



Kiessling said:


> Drive current isn't important here IMHO as all we measure is lux, and lux it is that we want to compare and calibrate to, not current. So ... if the lux readings are consistent over time I don't care about current. Or did I miss something and look stupid now?


Hi Bernie,

My concern about drive currents is that they *do* in fact affect lux readings. The currents probably will vary somewhat depending upon brand of battery and how quickly the voltage sags in the first minutes of run time.

If we could be absolutely certain that the converter regulated current to within a few tenths of a percent over the range of voltages to be expected with CR123A batteries then it's not a concern. However, I have yet to see a current regulator that doesn't vary by a few percent over its operational voltage range. I'm not saying it's impossible to design one, but rather that cost, size, and parts count considerations dictate that most current regulators are less than perfect. Remember that the eye won't pick up output variations of a few percent so it's not imperative to design regulators to regulate perfectly, at least for flashlight applications. However, the lux meter will pick up these variations.

-Joe


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## Sigman (Oct 3, 2005)

Tom, now just how much time do you have on your hands? Where do you come up with these ideas? This just makes tooooooo much sense! :thinking: :thumbsup: 

Glad you brought this up - count me in!


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## Brock (Oct 3, 2005)

On an A2 I can't imagine at 1 meter you could tell if the LED's were on or off. The hotspot would so wash out the LED's. Then again I have 3mm in mine, maybe they spread out the light a LOT more. Then again if your talking 1% maybe.

I guess my take on the point of all this was to sort of benchmark all our results. Heck even if the LED's were 10% brighter in your A2 then mine, how much of a difference would that make to the 99% introduced from the incan lamp?

Maybe I am confused though...


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## Bogus1 (Oct 3, 2005)

Are we seeing some mixing up of the SF A2 and the Aleph A2 in the comments? I was referring to Aleph heads in my post. Perhaps this is another reason to use an A1 head on the Aleph?


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## jtice (Oct 3, 2005)

hmm, the leds of an A2 are always on when the incan is on?
is that the issue you guys are worried about?

I thought it was off, led, incan, off.


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## SilverFox (Oct 3, 2005)

Hello Bogus1,

We are now talking about measuring 2 lights. One will be the Aleph 2, the other a regulated incandescent like the SureFire A2.

Tom


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## Bullzeyebill (Oct 3, 2005)

So, you would be measuring one meter from the front of the flashlight lens to the lightmeter sensor, which might be one inch off the floor, or so? This assuming you use a floor to place the meter.

Bill


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## SilverFox (Oct 3, 2005)

Hello John,

I believe the A2 sequence is LED on, Lamp + LED on, off.

Tom


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## bwaites (Oct 3, 2005)

The Surefire A2 twisty tailcap is:

Locked out, LED only (with tailcap push), Both (with tailcap push), LED only, Both.

There is no way to turn off the LEDs that I am aware of, and yes, in Lux readings it will make a difference at 1 meter. The LED's do contribute at 1 meter. Maybe not much, but they do contribute. If the incandescent lamp produces 50 lumens, the LED's are probably in the 3-5 lumen range. That's as much as a 10 percent variation. Using fresh cells will cut most of the variation out, and that is probably enough for our purposes, but there is some variation error, regardless.

Bill


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## SilverFox (Oct 3, 2005)

Hello Bill,

No.

We need to measure from the outside edge of the bezel. The lens is recessed about 1/8" or so.

Tom


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## bwaites (Oct 3, 2005)

The meter sensor should be placed in the middle of a wall, with no wall closer than 6 feet to the sides and 4 feet above or below to have most accuracy.

Ideally, the closest walls and floor/ceiling should be at least twice the measurement difference to avoid bounce variance. Most of us would have a hard time with that, though, since most ceilings are 8-9 feet. 

Bill


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## cy (Oct 3, 2005)

matters less how we all measure, just that we all do it the EXACT same way. 

sure would be nice to come up with a standardized way to measure as a result of these tests.


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## SilverFox (Oct 3, 2005)

Hello Bill,

You are correct, however this comparison is designed to see how much variation there is from one persons measurements to another's. I think we should ask people to take the measurement as they would normally do. When the discussion turns to why is there a difference, your suggestions would come into play.

Tom


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## yaesumofo (Oct 3, 2005)

I would like to partisipate on this projet as well please.

Yaesumofo


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## McGizmo (Oct 3, 2005)

Hi guys,
I can't keep up but that's OK since this will be Tom's baby! :nana:

Some points:

I will test the NexGen converter and I-out with a range of Vin's to see how much of a factor this might be. I would like to point out that the issues and concerns mentioned here are legit for the most part and yet we typically "allow" for lux measures reported on CPF where even greater variations to readings are likely being introduced and first and foremost is the light sample itself and followed by the fact that we have no handle on the consistancy in meters and methods. If one typicaly fires up a light and reads its lux (as I do) it is counter productive to specify waiting a half hour for warm up unless everyone is now planning on doing this for their readings?!?!

Pragmatically, I am hoping to get a sense that my meter is say 15% lower than the "norm" or to be established "CPF standard" and in the future, I will adjust my reported measures, accordingly.

I am inclined to go now with the Aleph 1 and SF A2 (PK will provide a light, BTW) and this should make things less confusing as well as like Bogus1 stated, the smaller spot of the Aleph 1 might be easier to read. :shrug:

As to the SF A2 and the LED's, the LED's may only add 3 to 5 lumens to the picture but after seeing the spectrum I will show below, I think they should be taken out of the picture for this program.







The bump at 470 nm is most likely due to the LED's agreed?!? At any rate, I will measure the A2 as well prior to sending it on to Tom. :shrug:


----------



## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



McGizmo said:


> Hi guys,
> The bump at 470 nm is most likely due to the LED's agreed?!?


Without question. The rest of the spectrum is a typical blackbody spectrum for an incandescent but that peak at ~460 nm will most certainly affect readings.


----------



## SilverFox (Oct 3, 2005)

Hello JTR,

If I understand your concern correctly…

You are saying that the regulator output is somewhat dependent on battery voltage. That suggests that if I use a cell with a different voltage, the lux measurement will be different.

I just did a quick check of some cells I have here:

SureFire 3.275 volts
StreamLight 3.267 volts
Sanyo 3.236 volts
BatteryStation 3.270 volts

Does that mean that if I use a Sanyo cell in one measurement and compare it to a SureFire cell used for a subsequent measurement, the 0.039 volts difference will influence the lux reading? 

Or

Are you concerned that the voltage under load for different cells will make a difference?

Another item for discussion… If my household power is 108 volts, and yours is 120 volts, will that make a difference if we build a power supply to run the light?

Tom


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## SilverFox (Oct 3, 2005)

Hello Don,

Thanks for contacting PK and talking him into letting us use an A2.

:devil: Perhaps we should think about including an HID light as well... :devil:

Tom


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## jtr1962 (Oct 3, 2005)

SilverFox said:


> If I understand your concern correctly…
> You are saying that the regulator output is somewhat dependent on battery voltage. That suggests that if I use a cell with a different voltage, the lux measurement will be different.


Yes, that is exactly what I'm saying. Here are some tests I did a while back on two of luxlover's flashlights:

Arc LSH:

Vin___Iout
2.00V 135mA
2.10V 303mA
2.20V 310mA
2.30V 402mA
2.40V 456mA
2.50V 499mA
2.60V 535mA
2.70V 561mA
2.80V 572mA
2.90V 574mA
3.00V 574mA
3.25V 596mA
3.50V 573mA

KL-1:

Vin___Iout
2.00V 390mA
2.10V 429mA
2.20V 462mA
2.30V 488mA
2.40V 510mA
2.50V 532mA
2.60V 556mA
2.70V 579mA
2.80V 596mA
2.90V 617mA
3.00V 635mA
6.00V 694mA

It might be expected that under load a CR123 might be anywhere from 2.5V to 3.0V with no real way of knowing one way or another from person to person. You can see for yourself how much the LED current varies over this range. The Aleph regulator might be better or worse. No way of knowing without testing.



> Another item for discussion… If my household power is 108 volts, and yours is 120 volts, will that make a difference if we build a power supply to run the light?


I can check that with my Variac. I have two of the supplies I recommended. I'll check them under whatever loads would be applicable for the lights we're considering testing (can someone please furnish me with that data?). I don't think there will be much variation of Vout with input AC voltage compared to the variation we would get with batteries.


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## HarryN (Oct 3, 2005)

I would like to be part of this as well.

I am "slightly" inclined to wait 2 - 3 minutes for stability before measuring, but 1 min is probably ok.

500ma is a great place to measure, as the heat sink / dissipation issues are lower.

Adding an A2 to the mix is great.

JTR - If you are worried about 123 cells, I can send you some.

For my testing, I will actually do an X scan through the beam with the ligth meter. I have a 2 x 2 x 8 footer board (approx 40 x 40 x 3000mm for the metric folks) that is marked off every 10mm. The light is positioned vertically facing up, and I take X scan data across the light at 1 meter to approximate what the wall would "see" for hot spot and corona.

This works ok for lights up to 1,000 Lux - I will have to wear sunglasses with a 3,000 lux light. HID - no way I am standing in front of one of those.


----------



## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



HarryN said:


> JTR - If you are worried about 123 cells, I can send you some.


Thanks for the offer, Harry.  I might take you up on it but lets first see how my power supply suggestion goes. I just priced some 123s locally at $14.99 a pair. :ironic: Even though they're $1.25 mail order the shipping costs would get me. Beyond doing the tests I really have no use for them so I couldn't spread the shipping costs over a lot of cells. I'm still inclined to think using batteries introduces an uncontrolled variable into the test setup.


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## chimo (Oct 3, 2005)

jtr1962 said:


> I'm still inclined to think using batteries introduces an uncontrolled variable into the test setup.



I tend to agree with jtr1962 here. The Nexgen is very good at current regulation over the battery life, however, the batteries could easily be taken out of the equation all together as a source of testing error with a very cheap linear regulated wall-wart type power supply.

Paul


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## bwaites (Oct 3, 2005)

The only way to use a power supply would be to use a regulated power supply.

I would prefer to use the power source common to the lights, since the regulation in the lights is supposed to keep it steady.

As far as the LED's playing a part in the measurement, Don and I are in agreement. I really would like them out of the equation. 

Tom, I thought we were trying to check meter consistency as much as accuracy of a measurement system. If we all use different setups, all we will know is that a bunch of variables play a part, not if the meters indeed are different. 

Don't we already know that variables play a part?

Bill


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## SilverFox (Oct 3, 2005)

Hello JTR,

Don is going to measure the NextGen at different voltages to see what the differences are. The draw from the batteries will be in the 900-1000 mA range.

All of the CR123 cells I tested stayed between 2.25-2.75 volts at 1000 mA, so we are looking at a maximum difference of 0.5 volts. There were a cluster of brands that were much closer than that, so we may be able to suggest those if possible.

Reviewing my test data, we may be better off to up the turn on time from one minute to three minutes to let the battery settle in.

Tom


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## jtice (Oct 3, 2005)

Great comments guys, this thread is bringing up alot of issues
that I think alot of us have been concerned about for a while.

As said, the way that we all conduct this test is going to make the difference.
We all need to make the testing conditions as alike as possible.
Heres a quick list that seems to be what everyone agrees on.


1 Meter distance between the front face of the lights bezel and light meter sensor
Allow light to run for 1 minute before taking a reading.
If your light meter has a Peak function, take a reading both using it, and manually.
Try to have the light and meter suspended in the middle of the room, with no walls, table tops, etc. within a few feet.
Use Fresh PRIMARY Cells (NO Rechargables)
Take note of the cell Brand and voltage before the test.
Give details on your Setup. Light Meter Model, Positioning, Room Lighting, if the meter read 0 before the test, etc.
Let the light sit in your house for a while, so the light is room temp. (dont do the test, with the light straight out of the box, cold from sitting on the porch)

I know Im forgetting something :green:

~John


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## McGizmo (Oct 3, 2005)

Hi guys,
OK, I have the NexGen I plan to use and it is in an ES-Can with long leads soldered onto it. I connected these leads to a bench LuxIII star that has ben abused for some time now. I have an Extech clamp on amp meter for measuring current to the LED. I just varied the Vin by a volt and recorded I-in and I-out to the LED:

Vin I-in I-out
2.20 1005 mA 508 mA
2.40 871 505 
2.60 861 506
2.80 722 506
3.00 674 506
3.20 642 509

Now I want to state that I-in would bounce around as much as +/- 10 mA but I-out would settle in at +/- 1 mA within 5 to 10 seconds. 

If you guys think that going to a inexpensive power supply will provide a better "fix" on constant current to the converter, then by all means. I think it is unlikely. I believe a fresh CR123 will fall in the Vin range I have tested above.


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## Quickbeam (Oct 3, 2005)

I'm in. I have 2 meters to test.

Suggestion: Make the instructions very detailed, unambiguous, and include a copy with the package.

I have a tough enough time keeping up with my own site, let alone CPF lately, so;

TOM (Silverfox), if you could let me know when things are ready to go via e-mail, I'd appreciate it.

Doug P.


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## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



McGizmo said:


> If you guys think that going to a inexpensive power supply will provide a better "fix" on constant current to the converter, then by all means. I think it is unlikely. I believe a fresh CR123 will fall in the Vin range I have tested above.


Wow, that regulates better than anything I've tested to date. Variation over voltage is less than 0.8%. The 2.2V data point might be about what we can expect with 2 NiMH cells, so we have the option of allowing the tester to use either lithiums or NiMH with no appreciable effect on test results, provided you provide both battery tubes.

However, the power supply option remains fairly cheap and easy to do. If you count the cost of all the new cells which will be used, it actually comes out to less, and as a bonus we can test unregulated incandescents without worrying about the state of the battery. Also, given the NexGen converter's regulation ability I think any small variation in supply voltage will be a complete non-issue. At this point it doesn't seem like it's much of an issue even with batteries.


----------



## jtice (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

I must say, thats some impressive regulation !!! :rock:

Seems like a fresh cell should do ojust fine, no need for a PS here.
This way more ppl can test it also.

~John


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## SilverFox (Oct 3, 2005)

Hello Doug,

Thanks for joining in. I will make sure that you know when things are headed your way.

Tom


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## SilverFox (Oct 3, 2005)

Hello Don,

Very impressive. That seems rock steady to me.

I'll make an executive decision and say that we will go with batteries.

JTR, if you want to take another set of measurements with a power supply you are welcome to do that, and I would hope you would present that data as well. If you need some CR123's, I will make sure you get some.

If anyone else does not use CR123 cells on a regular basis, please contact me. There is no reason to pay very high prices for these cells at a retail store when we get them so much cheaper. I have a good stock pile and should be able to help out.

As a matter of fact, I believe i can get Wayne at AmondoTech to donate some of the Titanium 123's. They will be just fine in this application.

Tom


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## SilverFox (Oct 3, 2005)

I think this is a good time to restate our goals for this project.

First a bit of history…

This project idea came about because of some interesting measurements I observed on my Aleph 3. I was on a camp out and was demonstrating (showing off…  ) some of my lights and explaining how light falls off with distance. We took a lux measurement at three meters after discussing how reflectors collumate the beam and it may not be fully developed at closer distances. We then converted it to lux at one meter, then measured out the distance where we should be down to one lux by taking the square root of the one meter number. I was very pleased to find out that the numbers matched.

I would like to point out that a forest is a great place to measure lights. It is naturally free of reflections, and we had little to no ambient light pollution. 

I went on to measure several other lights. Our demonstration was done on the low setting of the Aleph 3, and when I measured the high setting, I came up with a very high number.

I called Don to try to figure out what was going on. I have altered my Aleph 3 a bit, but did not think that this should have such a high impact on the lux measurements. I am reading about 70% higher than anyone else with an Aleph 3 has reported. For the record, don’t ask me to modify your lights… I don’t know what I am doing…  

Our discussion came down to either I had done something correct with my light, or my meter was a “bit optimistic.” We then started talking about how to check a meter and that led to a discussion of a possible CPF standard light source, and now here we are.

Now, back to the goals…

I would like to take a measurement of a light and have a good feeling that when I say what I got, others will be able to also get close to the same readings. I know there are a lot of variables, but I believe that if we outline a proper procedure, we will be able to address those issues. If I find that my meter is reading high, I will not that when I report in the future and make an adjustment for it.

The calibration curve I received with my meter shows that it looses sensitivity towards the blue end of the spectrum. I would like to know what effect that has on my measurements.

I have no idea about how far off the different meters will be, but it is going to be interesting to find out.

In addition, Don and PK are donating these light sources to CPF. That means that they will be available in the future for new members who join CPF, or if you happen to get a new meter and want to check it out. 

A Lux3 driven at 500 mA should give long stable life. I am hoping that we will be able to get thousands of tests from it before it begins to fade. The A2 may be a bit of a problem when the lamp burns out, but we will just have to deal with that issue when it comes up. However, a quick trip through Don’s integrating sphere should give us an idea if an offset is required for a new lamp.

If all our meters read exactly the same, we will KNOW that we are doing everything right. If some meters are off, we will gain an understanding of that and can make appropriate adjustments in our reports. All in all we will get a chance to handle (although for too short a time  ) a couple of very fine lights.

Tom


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## rdshores (Oct 3, 2005)

I think using the battery with the NexGen is regulated plenty good enough. With the power supply idea, one variable would still be variations in mains supply voltage from your power company. This could affect the regulator as much as battery vaiations. Another option could be to covert the light to use AA batteries and then have everyone use the same brand of battery, say a Duracell.


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## georges80 (Oct 3, 2005)

SilverFox said:


> Hello Don,
> 
> Chris at Sphere Optics mentioned that he might be able to do a sample for us at a greatly reduced price (maybe free). Perhaps we could include him on the list...
> 
> Tom



Funny - he's visiting the Bay Area Wed/Thurs/Fri. I just talked to him today about purchasing an integrating sphere (4" about $1K - with a 25-30% discount for 10 units) for work.

I just found this thread via a PM - I'll have to read it later tonight/tomorrow and hit him up on Wednesday when he visits the company where I'm contracting.

george.


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## SilverFox (Oct 3, 2005)

Hello George,

That's great.

What we are looking for is an accurate measurement from an incandescent light and a LED light. We will provide both lights and batteries for them.

We are interested in

Lux at 1 meter,
Lumens,
and a spectrum plot of both lights. 

Tell Chris that Don is using a USB-2000 spectrometer and we are looking for a calibrated confirmation of his set up.

Of course, we would like it for free...  but if that is not possible, get the best deal you can.

Tom


----------



## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



SilverFox said:


> JTR, if you want to take another set of measurements with a power supply you are welcome to do that, and I would hope you would present that data as well. If you need some CR123's, I will make sure you get some.


The power supply data would require setting the light up to work with the supply. At best I might be able do something temporary with alligator clips so I can use my supply. If I can't do it with alligator clips then I'll just go with the batteries. I don't want to do anything to alter the light(s) permanently. 

On the battery "problem", I'd suggest just including the extra tube which lets the tester choose between AAs and 123s, whichever is more convenient for them. I was at first a little concerned that the regulator wouldn't regulate properly at the ~2.2V that 2 AA NiMH would give under 1 amp load. However, those concerns are apparently unfounded. Whomever designed the NexGen converter did a great job.

The SF A2 regulator needs to be tested now to make sure it also behaves well with variations in input voltage. If it doesn't then the power supply might be the only way to go.

BTW, I think some people here were a little confused about the power supply idea when I heard things like not using a power supply will let more people participate. The idea wasn't that everyone has to buy a power supply. Rather, it was that we would have _one supply_ which would be sent along with the test lights. I should have been clearer on that. And yes, I could check out the power supply behavoir with variations in AC voltage to see if that would be a concern.


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## chimo (Oct 3, 2005)

McGizmo said:


> ```
> Vin           I-in              I-out
> 2.20      1005 mA            508 mA
> 2.40        871                 505
> ...



Wow, those are great figures. Looks like a separate power supply would not be worth the effort.

Paul


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## tvodrd (Oct 3, 2005)

My 631 could use a reality check and I have a _Meter Stick._ I'm in. 

Larry


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## PEU (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Tom: I'm in , but put me at the bottom of the list since shipping back and forth from USA to Argentina will take a month just for shipping.

I also have a LM631.

:thanks: 

Pablo


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## jtr1962 (Oct 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



rdshores said:


> With the power supply idea, one variable would still be variations in mains supply voltage from your power company. This could affect the regulator as much as battery vaiations.


I just checked out the power supply I recommended earlier. At no load the output is 3.345 volts and this changed by less than .001 volt as I varied the AC input from 70 VAC to 140 VAC with my Variac. For load testing I used a 2 ohm resistor which gave me a load current of about 1.65 amps. The output voltage at 120 VAC input was 3.315 volts and again this varied by less than .001 volt as I varied the AC input from 70 VAC to 140 VAC. I think it's safe to say that mains voltage will not affect the results here, at least with this power supply.


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## McGizmo (Oct 3, 2005)

JTR,
I suppose I could fabricate some type of battery eliminator that could take input from a power supply but I think we are getting too "tight' on this idea. It is interesting to me how some are willing to report a lux of x on an ACME Photon Lobber and many assume that they will also get X lux from a different member of the ACME population and regardless of batteries used.

I believe Bill suggested measuring an incan as well and I suggested the A2 since it at least has a voltage regulator and is much less prone to the DD variations of the typical incan. If it can give a flat light output from a fresh SF CR123 up until the point that the batteries fail to provide the power to maintain regulation then I submit that the Vin, under load does see a reasonable range that new CR123's should fall within? :shrug:

Chimo,
Wayne Y. (Dat2zip) designed the NexGen driver and all of his drivers that I use are "constant current". He has the madmax which isn't. Certainly there is more variation in some of his other drivers but by and large, the point to a constant current driver is to provide constant current!! All of these drivers will have a limited range of Vin but within that range, the current is reasonably stable and close to target. The NexGen has really impressed me as a driver that is efficient and very consistant not only as an individual but within the population. I don't think I have seen any NG 500 that has been beyond 10% of the target 500 mA and the individual has always been very stable at its own particular level. 

500 mA to a UX1J is not excessive nor should it present any thermal issues of magnitude to skew some light readings, IMHO. The LED that I am going to use is still running at 500 mA and stuck in my integrating sphere. I have no idea how close or far I am from absolute readings but the LED presented to the IS in its bald and bare state is reading 71 lumens at the 500 mA. Makes me wish I had snagged this LED for a personal light! :nana: It should be a cool sample for a "CPF Standard" pass around.


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## Darell (Oct 3, 2005)

I'm pretty sure that we should only consider testing during a full moon to account for gravitational pull.  

Sorry! Couldn't help commenting from the peanut gallery! I agree with Don that there comes a point when this stuff just goes WHOOSH right over the top. At some point we're going to have to accept some small amount of variability - there really is no other choice. The differences in battery starting V are all but insignificant when using a curent-regulated light... and when we consider all of the OTHER variables going on.

We're bound to get finger prints on the window, have differences in humidity and temperature... the list is endless.


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## cy (Oct 3, 2005)

impressive performance by a nextgen!

with a flat current range delivered by NG. would gain very little by shipping a regulated power supply with lights.


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## nemul (Oct 3, 2005)

i dont have a light meter, but this is a cool idea!


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## SilverFox (Oct 3, 2005)

Hello Darell,

Thanks for reminding me...

Everyone handling the lights should probably wear gloves... :nana: 

No, really, we need to make sure to check the lens to make sure it is clean before testing.

Tom


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



Darell said:


> I'm pretty sure that we should only consider testing during a full moon to account for gravitational pull.


You have to be able to somehow apply an adjustment in an Excel spreadsheet for lunar orbit since the pull of the moon can cause light to curve less in the gravitational well of the Earth. It can affect lux readings by as much as 0.00000000000001%, a not insignificant amount.  

Seriously, I don't think I'm going overboard here with my earlier ideas. I'm just trying to eliminate some of the more obvious variables under our control from the equation, or at least determine if they're relevant. We established that battery voltage with the NexGen regulator isn't really as big a factor as I thought it would be. If the light output of the A2 is flat (to within about 1% or less) for most of the battery life then I submit that it's not an issue there, either. However, we should establish that one way or another _before_ the tests, and if not agree on how to deal with it. Remember that I suspect variability between light meters will be under 10%, perhaps even under 5%. If we don't deal with something which can potentially affect light output by 5% or more then it will make the results less than what they could otherwise be.

I'll also point out that part of the reasoning behind my power supply suggestion was to make things easier for the testers as well as more consistent. No need to worry about batteries at all. Just plug the supply in, connect it to the light, and test away. Far easier than opening the light and inserting batteries. Far less chance of things going wrong (batteries inserted backwards, batteries exploding, etc.), and no worry about things like contact resistance potentially affecting the results. I _never_ use batteries for power when I run tests because they simply introduce too many potential problems.

Anyway, the power supply idea is out unless some compelling reason for it comes up. The only thing I can think of right now would be if the A2's output isn't nearly flat over battery life. We've already established that voltage over battery life is a non-issue with the NexGen regulator and I'm glad we did. The converse easily could have been true, leaving us all scratching our heads at the results.

Last thing on my mind is warm-up time. We need to plot the output versus time at least once. Now it is entirely possible that the light might take 30 minutes to reach its final value but will be within half a percent of that value after, say, five minutes. In that case, a warm-up of five minutes will be good enough for the purposes of this test. The A2 probably needs no warm-up time at all, or certainly no more than a minute.

BTW Darell, if you think I'm being anal here you should the lengths I go through when I'm doing things for myself. A few times I actually repeated several weeks of work because I didn't account for variables which affected the results by hundreths of a percent. Another time I rebuilt the entire power supply section of my thermoelectric temperature chamber to gain a couple of percent efficiency. And don't ask me how many iterations I had to do on the thermal parts of that chamber before everything worked exactly as I wanted it to.

I could probably think of 10 more variables which would affect the results of the testing here to some degree but I also know when to stop. Once the affect of a variable is way less than the precision of the instrument being used to measure it then you can usually not worry about it. Notice that I'm not overly concerned here about things like dust in the air which will certainly affect results somewhat depending upon how much of it there is. The reason-1 meter of dusty air probably attentuates the light less than a tenth of a percent over what a vacuum would. The other nine hypothetical variables might affect the results in total by a few tenths of a percent. I'm not concerned since that's well under the precision of any light meter we'll be using.


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## McGizmo (Oct 4, 2005)

jtr and all,

I can solder lead wires to the NexGen and make a simple dummy battery tube. I can also solder lead wires to the A2 lamp module and fake a dummy battery tube for it. This will reduce the contacts to your lead connections between power supply and these leads. If this is what you guys want to do, cool, just let me know. We loose some mobility and of course we are perhaps closer to measuring a more consistant standard. I personally am comfortable with the NexGen's ability to overcome the resistances in the mechanical contacts of the batteries and their voltage under a fresh cell condition. I have not done a run time on an A2 to know just how flat it is and how well it maintains constant voltage over some range of Vin. :shrug: The A2 was an "add on" to the program here.


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## SilverFox (Oct 4, 2005)

Update:

I have edited my first post to reflect what we have discussed today.

I changed from one light to two lights and all of my edited comments start with EDIT: and end with END EDIT.

Tom


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



McGizmo said:


> jtr and all,
> 
> I can solder lead wires to the NexGen and make a simple dummy battery tube. I can also solder lead wires to the A2 lamp module and fake a dummy battery tube for it. This will reduce the contacts to your lead connections between power supply and these leads. If this is what you guys want to do, cool, just let me know. We loose some mobility and of course we are perhaps closer to measuring a more consistant standard.


Well, since this is SilverFox's idea I'd say he ultimately has the final say on using a power supply but I'll give my nod for this idea. So what we would have is a battery tube with two wires coming out if I understand you correctly? Very easy then to solder those two wires to a standard power supply jack and use whatever off-the-shelf wall wart is appropriate. The supply I mentioned will be perfect for the Aleph in terms of Vout and current capacity. What are the supply requirements for the A2 in terms of voltage and current? Things might get too complicated if we need two separate supplies (greater chance of someone connecting the wrong supply and blowing something out, although we can get around that with different plugs/jacks). If 3.3V will serve both lights then I'm 100% for the supply idea. If not, then maybe we can still use one supply, and someone (me?) can make a regulator to put inline for using with the incompatible light, or we just use two supplies with different connectors to prevent a mixup.

EDIT: I read the edited first post. The A2 takes 2 CR123s but accounting for voltage sag under load and end of life battery voltage it _might_ still be in regulation at the 3.3 volts of the recommended power supply. Therefore, one supply might work for us.


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

While on the subject of batteries, I think everyone doing this should be using a fresh or near fresh battery in their light meter. Usually design parameters of test instruments are based on the voltage of a new or near new battery so a nearly depleted one might affect readings.


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## andrewwynn (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

although that's a 'variable' that wouldn't necessarily fit.. we measure how we measure.. but it does make a lot of sense .. i think it'll be fascinating to see the results of this experiment... I have a feeling that some people will be discovering that their meter is shorter than others if we use the 'string' method i recommend for the meter measurement.. 39.37" long from the bottom of a small weight to a tiny knot in the string.. it wouldn't hurt to have a small plastic square included in the kit... so we can make sure to get the height correct.

example.. put light meter on the floor near the corner of a door or door jam.. put the angle down on the top of the meter and put a piece of tape on the door at the base of the triangle... now measure up with the string exactly 1m... put another piece of tape.. now use the triangle to get the exact height of the bezel to the top of the light meter... if using the edge of a door and going away at a 45 deg. angle from the corner there will be very little light reflected from the door to the meter to throw off measurements... 

it would be VERY useful to have a 'standard' of setting up like i just recommended.. but also just 'do it how you do it now' and have both sets of measurements!

The idea of a power supply makes a lot of sense to make sure the voltage is identical.. a simple wall-wart, dummy cell with a zener diode inside and an appropriate series resistor will get a dead-on constant voltage.. it'd take a bit to get that inline resistor right but i think that it'd be worth it. 

-awr


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## SilverFox (Oct 4, 2005)

Hello JTR,

Good point about checking the battery in the light meter.

Tom


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## Darell (Oct 4, 2005)

jtr1962 said:


> BTW Darell, if you think I'm being anal here ...


Sorry, jtr! I didn't mean to point fingers at anybody, and truth be told - I'm one of the most anal guys I know (fortunately, I don't really *know* you, so I can say that).

I just didn't want to get this program derailed by the details. Since we're trying to discover the variables of the meters themselves, it is obviosly better to have the smallest number of variables in the test samples. But there comes a point....

Being light-meterless at this time, I'll do what I should have done earlier and shut my trap and just sit here quiety. You KNOW how well I do that!


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## SilverFox (Oct 4, 2005)

Hello Darell,

Please feel free to join in at any time.

Just because you don't have a light meter does not mean that we can not benefit from your extremely detailed perspective of the test method...  I was looking for a way around calling you anal, and this is the best I could come up with on short notice... :nana:

By the way, YOU are the reason we are doing this testing.

If you hadn't been so extremely anal about building such an excellent Aleph 3 for me, there is a good chance this light meter question would have remained philosophical. 

Tom


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## SilverFox (Oct 4, 2005)

Hello JTR,

Let me clearly state that your "extremely detailed perspective" is welcome here.  

Although I would rather just put some batteries in the lights and go from there, I am listening very closely to your ideas.

Tom


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## Darell (Oct 4, 2005)

SilverFox said:


> If you hadn't been so extremely anal about building such an excellent Aleph 3 for me, there is a good chance this light meter question would have remained philosophical.


Aw jeez. Now I hope that I at least wiped the fingerprints off of the thing before shipping it. 

Mostly this thread is getting me itching to buy another light meter. Anybody have an extra or care to share the current best place to pick one up?


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



SilverFox said:


> Hello JTR,
> 
> Let me clearly state that your "extremely detailed perspective" is welcome here.
> 
> ...


Thanks Tom.

I'm happy to offer my (anal) perspective wherever relevant.  

I think any final decision on whether to use batteries or not should wait until we determine the behavoir of the A2 with regard to battery voltage. If it's not an issue, then maybe going with batteries is the easiest route. If it is, and we need to have the A2 run off a power supply, then we might as well use one for the Aleph as well.

As for the issue of people not having 123 batteries, I think I might be the only one here with that problem and it's easily rectified by someone sending me some batteries for the tests.

I think I'll stop here for now. If I start thinking about this too much I might come up with yet more ways to make the tests more consistent (and everyone's life more complicated). :naughty: Come to think of it, maybe we should account for the phase of the moon somehow because.... :laughing:


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## SilverFox (Oct 4, 2005)

Hello Darell,

It may be more prudent to wait to see the results of the testing before purchasing a meter...

Tom


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## Darell (Oct 4, 2005)

Excellent point Tom! Seeing as how prudence and Darell go together about as well as oil and water, I hadn't even considered that.


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## McGizmo (Oct 4, 2005)

OK guys, the SF A2:

Here's a spectrum screen shot:







And here is a run time graph:






Now aside from the goofy dip at about 5 minutes or so, the low was 2193 lux and the high was 2280 lux for the duration of regulation. I happened to walk by when the light was in the zig-zag mode and I shut it off and then left it to cool off (hot to the touch!). Regulation was 48 minutes. I suggest that after 40 minutes, the likely voltage under load was reasonably less than that of a pair of fresh cells and yet the light output was as good as early on?!?!

INHO the effort of making a battery eliminator package that will have good contact with both the + and - contacts within the head is more trouble than the potential gain one might get from using a power supply over a fresh set of primaries. :shrug: I leave it up to you guys.


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## HarryN (Oct 4, 2005)

Gee Don, you're getting pretty good with those meters. Soon you will have a hard time calling yourself a novice.


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## rdshores (Oct 4, 2005)

Let's include a Meterman LM631 with the light. Then everyone can see how much their own test method varys from each other. To me, this data would be just as helpful as any other.


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## Kiessling (Oct 4, 2005)

I still do not get it why we want to burden ourselves with thoughts about drive currents, power supplies, heat generated, efficiency etc.
After all, what we want is a stable lightsource that delivers a constant lux measurement over some time. How this is achieved ... I couldn't care less. As long as Don can show us this nice and flat runtime graph we do not need to know how it is achieved, because we do not care about that right now. Just a calibration light source with a proven stability. Nothing more, nothing less. All the rest is insignificant to the task and can only add complications IMHO.

bernie


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



McGizmo said:


> INHO the effort of making a battery eliminator package that will have good contact with both the + and - contacts within the head is more trouble than the potential gain one might get from using a power supply over a fresh set of primaries. :shrug: I leave it up to you guys.


Thanks for doing the tests Don. The maximum variation of the A2's output over the battery life is a bit under 4%, and the sawtooth pattern as the batteries run down concerns me. However, based on my experience with electronics I think this may _not_ be a function of the changing battery voltage but rather some thermal issue with some component in the feedback loop heating and cooling slightly which in turn affects the drive current. The fact that it occurs over almost the entire graph and with an interval of roughly 2.5 minutes points in that direction. Therefore, you would probably have the same sawtooth pattern running the light on a power supply.

My conclusion at this point is that I agree nothing is to be gained from a power supply other than added weight and complexity. I simply suggest that with the A2 the testers try to record the highs and lows of the sawtooth wave so that we all have a common basis of comparison. If we do otherwise, then our readings can differ by up to nearly 4% even using the exact same light meter and testing conditions depending upon whether you recorded a peak, valley, or something in between. There we go, another variable eliminated. 

Now someone's going to have to send me batteries when it's my turn.


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## jtr1962 (Oct 4, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



Kiessling said:


> I still do not get it why we want to burden ourselves with thoughts about drive currents, power supplies, heat generated, efficiency etc.
> After all, what we want is a stable lightsource that delivers a constant lux measurement over some time. How this is achieved ... I couldn't care less. As long as Don can show us this nice and flat runtime graph we do not need to know how it is achieved, because we do not care about that right now. Just a calibration light source with a proven stability. Nothing more, nothing less. All the rest is insignificant to the task and can only add complications IMHO.


Good question, Bernie. Yes, ultimately my concern was that we have a light which is stable over the battery life. Since drive currents affect output, then that basically means I wanted to establish that the drive currents are constant as the battery runs down. Don did so to my, and I hope other's, satisfaction. Yes, the light output of both lights varies slightly, but the variation isn't great enough to be a concern for the purposes of this test. However, we _had_ to establish that for a fact before the testing began otherwise we wouldn't know if differing results were because of different batteries or real differences in light meters.

Now that we got that out of the way, let the testing begin....


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## SilverFox (Oct 4, 2005)

Hello Don,

It looks like we are good to go with batteries.

Thanks for checking the A2 out.

JTR, PM me your address and I'll get some batteries headed your way.

Let me edit the final test procedure and we will get things underway.

Tom


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## cy (Oct 4, 2005)

suggestion of including a 631 meter is a good one. 

this would verify your particular test setup is duplicating a known to be correct reading. 

but this adds yet another layer of complexity. 

Simple is good


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## andrewwynn (Oct 4, 2005)

I would say this is pretty solid evidence that the regulator will do it's job with batteries for this experiment. There is that very interesting 'flat spot'.. at about 10 minutes.. too bad we couldn't figure out exactly when that happens, we could all take the measurement in the middle of that time-frame if it's repeatable. .. the little sawtooth waveform is very interesting regulation. 

-awr


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## SilverFox (Oct 4, 2005)

If you would like to join in on this, you can sign up here.

Tom


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## PeterW (Oct 5, 2005)

We NEED to send an incan along too. Sending an incandescent will show the scale and calibration offsets between the lightmeters, whereas the LED lights will also show up spectral differences. All the lightmeters will have been calibrated with a tungsten light with a colour temperature of 2856K, so it makes sense to measure a light with a spectrum that is close to this. Doing 5 or more measurements spaced over 5minutes or so ought to show up any 'funnies', as long as people send us all the numbers.

Having a laser pointer fixed to the Light so that we could all repeatably position the lightmeter with respect to the light would be useful, having a diffuser and taking the highest vaue is the next best thing though.

The temperature at the time of the calibration should be noted. Temperature could give us some differences, maybe nice to deliberately do some measurements at a range of extremes to see how bad this could be. (You guys in the US get more extreme outdoor temperatures than we do in the UK!). Of course the way the light is held and used will determine the LED temperature, which is a big unknown and not stabilised.

Cheers to Tom for organising this. This sort of intercomparison will give us a handle on the sort of spread of values we see in commercial meters. I'd love to have a copy of the final data to have a look at. As mentioned there are lots of variables at play, we can work on these when we have the results in.

People should also give an estimate of the uncertainty of thier measurement of 1m (especially if they are moving the beam around to get the max reading). The measurement should be made in a dark room, preferrably with some dark material behind the lightmeter to reduce the effect of scattered light.

Maybe we ought to measure the meters are several different distances, then we could also get some info on meter linearity (maybe in the future).

Details of McGizmos kit would be interesting! The spectrometer sounds like a small ocean optics one, grating array instruments are known to have issues with stray light in the blue (though manufacturers are trying to address this issue). Integrating spheres are also themselves a source of numerous corrections and uncertainties, so much so that national labs now use gonio measurements to get the absolute numbers. 

Seeing that the whole world uses SI (including the US lab NIST) I think we ought to keep to using the meter. 

Sorry for the bitty nature of this post, I only had a few minutes to write it!

Cheers

PeterW

PS Don't include a lightmeter as we do not want people to have any idea what the 'correct' answer is!


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## SilverFox (Oct 5, 2005)

Hello Peter,

PK of SureFire has donated a regulated incandescent light - the A2 - that will be passed around as well. This light normally has 3 LED's in it, but they have been removed for the purposes of this testing.

There are a couple of goals that I hope will be realized from this testing. 

I have advised people to report their numbers as they normally would. Then, if they want to tidy things up a bit by paying closer attention to the alignment, eliminate reflections, and so on, to then report another set of numbers.

This should give us information on the differences in brands of light meters, and an understanding of how our surroundings influence our readings.

If you purchase a flashlight and during a review mention that you recorded 2500 lux at 1 meter from it, and I go and get the same light and only read 2000 lux at 1 meter, I wonder what is going on... Is my light different, or is your meter off, or is my meter off, or is the way you are taking the measurement off, or is the way I am taking the measurement off. 

This testing is designed to address the latter issues. 

If through this testing, I find that my meter reads 200 lux low, and you find that your meter reads 200 lux high, we can make adjustments and realize that we have basically the same light.

Tom


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## The_LED_Museum (Oct 5, 2005)

It's funny; I've got plenty of CR123A cells, but no AA cells. :sick2:
With other participants of this metering/passaround, the opposite is true. :green:


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## georges80 (Oct 5, 2005)

SilverFox said:


> Hello George,
> 
> That's great.
> 
> ...



Had a bit of a talk with Chris regardining testing etc. I didn't notice the part above that said you would like them to perform some testing on the 'gold standard' lights. So, I focussed on the equipment - anyhow, he filled me in that you've been talking with him a lot and that doing a 'group' buy of an integrating sphere etc was a "good idea".

So, I never got into the testing issue - sorry.

He also did a pretty good job of convincing me that with LEDs, HIDS etc, the use of our standard LM631 etc for comparing readings is near to useless due to the response curve of light meters. Even if we 'calibrate' our light meter to a gold standard LED our comparative readings would only match for that LED - the next LED that comes along with a different 'colour' and we again couldn't compare readings between light meters.

The only correct way to do this is with a spectrometer and an integrating sphere...

george.


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## SilverFox (Oct 5, 2005)

Hello George,

Thank you for taking the time to talk with Chris.

I happen to agree with you and Chris, but it is not practical for us to do that. Don has been working for a couple of weeks just to get to the point where he is almost comfortable taking a measurement. 

Not all of us have an extra $6-10k to invest in our own set up, nor are we able to spend a couple of weeks getting familiar with it.

Many of us do, however, have a light meter...

This round of testing may reveal that our meters are closer in agreement than we think. On the other hand, the scatter may be so great that we may insist that people refrain from mentioning lux readings and save the money they would spend on a lux meter and use it to buy another flashlight.

It would be nice if we could send our meters to the laboratory and have them calibrated over a variety of light sources, but I am not sure that is going to happen either.

In spite of the shortcomings involved in this type of test (both those discussed and those we have not thought of yet...), I feel that we can get some very useful information from doing it.

I believe we all understand the no two LED's are going to be the same, and that incandescent lamps age with use. It could probably also be stated that no two light meters will agree. However, I believe that these test results will give us an idea if our readings are + - 10%, or + - 100%, or something in between.

Tom


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## McGizmo (Oct 5, 2005)

At some level, anything we do will be wrong and since our eyes are all different, it is a moot point to even go by the lumen standard since it is based on human vision in general and not *me* in specific! :nana:

Without having a feel for the magnitude of correctness or incorrectness of our light meters, I am not willing to throw out the utility of comparing the same light to see what variations we experience. A spectrometer and Integrating Sphere is great for measuring absolute radiometric power or lumens if the system is properly calibrated but it won't tell one didly about collimation of the beam?!?!? :shrug:

Perhaps we are all limited to relative comparisons among lights using our own equipment and with no sense of adjustment to a common standard and then again, perhaps we can get closer to a common means of measure. These guys who tell us that we need $20k in equipment or give it up are correct at some level and then again at a more relaxed level, they are being too limited in their acceptance of "ball park". The vageries of individual optics and lamp outputs are most likely much greater than the accuracy of our measuring equipment.


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## Roy (Oct 5, 2005)

In my college days (40 years ago) I remember in Chemistry 801, calculating the total error of a proceedure that involved combining the +/- error of EACH device used in the proceedure. Anyone remember how this was done? 

For those that want absolute accuracy, the error of measurment needs to be accounted for for each measuring deviced used. My light meter adapter has a stated error of +/-5% and I have no idea what the error of my DMM is (probably less that +/- 10%). 


Remember....your results should be based on multiple measurments and averaged.....especially when trying to measure the peak light level in a beam pattern. The results would be reported as 1000LUX +/- 10LUX ...for example.

A simple comparison to a known source is all that (IMHO) is needed for our purposes. We are not in the calibration business.


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## georges80 (Oct 5, 2005)

SilverFox said:


> Hello George,
> 
> Thank you for taking the time to talk with Chris.
> 
> ...



Agreed - it's a lot of money and only appropriate for someone that really cares about the readings - even a company would find it hard to justify unless all companies used the same metric to quote 'specs'.

It will be interesting to see how the light meters compare, i.e. are we within 10% or 100%. Though, it would be interesting to have a couple of LED bin codes in the testing, i.e. add in another dimension (spectrum variation) to the light meter comparison tests.

george.


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## wquiles (Oct 5, 2005)

I have an LM631 from the Group Buy a couple months ago. I would love to take part in this 

Will


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## chevrofreak (Oct 5, 2005)

Found part of my problem, a reflective surface was bouncing a lot of the spillbeam at the meter but the regulated light I used to check my meter has very little spill so there wasnt much reflection. I think I'm going to build a box to put my meter in, painted flat black with a textured surface. Maybe some rubberized undercoating.


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## McGizmo (Oct 6, 2005)

Hey guys,
If you want, I can also include a K2 blue/ NG500 in an Aleph 1 head and you can meter it as well as the white LuxIII and the SF A2. The blue is definitely a low achiever in lumen measure as well as lux. It is likely at the fringe of what the meters are designed for so it might be interesting to see what numbers folks get. :shrug: You can swap heads on the same body for measure.


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## PeterW (Oct 6, 2005)

The defined (CIE1931) eye response was based on a small group of people in London in the 1920's. It is said that it is best matched by a woman in her late 20's, who will go out of calibration in around 8 years or so. So most of the forum members are 'not in calibration' and will see things differently.

Uncertainties (proper word for 'errors') can be combined in a whole variety of ways. The ISO Guide to uncertainty in measurement (aka 'the GUM') tells you what to do. Of course it is incomprehensible and very few people understand it. It depends on what uncertainty contributions you have and what you want to do with them. (I do this as part of my job and probably ought to write some simple guide, if I ever get any free time).

The problem of LED measurement will be sorted (eventually), maybe using small and cheap spectrometers, perfect photometers or through better manufacturing control and specification data.... we shall see. People are working hard on this issue, it is just that the technology is moving so fast!

PeterW


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## SilverFox (Oct 6, 2005)

Hello Don,

I would be happy to add a blue measurement to the mix.

I know that according to the calibration chart supplied with my meter, I should read low at the blue end of the spectrum.

Tom


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## SilverFox (Oct 6, 2005)

What do we mean by repeatability?

It is my humble opinion that repeatability means that we set the light up, take a measurement, then put things away. 

I am suggesting that we repeat this 3 times, then report our average reading.

If your metering station is permanent, and you mount the light on a tripod or other holder to take your measurement, you would remove the light from the holder, move the holder, then set the light and holder back up again.

If you metering station is portable, you would have to move the meter, the light, and the holder, then reset everything back up.

This should account for variations in angles and distances, and will give us some practice in finding the peak spot in the beam.

Comments?

Tom


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## HarryN (Oct 6, 2005)

Perhaps we are starting to miss the fact that this will be a combination of "testing" and "learning". I am certainly assuming that the first time we circulate these lights, my results will be "A" and as we / I get better at understanding the results / procedures of others, the results of the "next time" we circulate the lights will be "B". 

I might even own different equipment by then.

If I have learned nothing else from being in CPF, it is that we all learn from the information / postings / procedures of others. I suspect that the results will start to tighten up naturally as we go through the process a few times.

Some people may even learn how far away 1 meter is.


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## SilverFox (Oct 6, 2005)

I have edited the first post to reflect the addition of the blue K2 - Thanks Don.  

I have also spelled out the repeatability measurements.

We are just about to get started on this. I am glad that everyone is in agreement on the proceedures...

It's time to get things going.

Tom


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## SilverFox (Oct 7, 2005)

Why are there errors in Light Meter Measurements? 

We spend a lot of time discussing the various merits of flashlights. There are several choices in lens material, reflectors, drive methods, etc. Then we go on at length discussing the various bins of LED’s and how tint can effect our perception of the things we illuminate.

I would like to explore, for a few moments, the concept of measuring light. Please understand that my qualifications are that I know nothing. Well… not quite nothing, perhaps I can state that I know enough to be dangerous…

We all understand that light exists in a spectrum of wavelengths that we can loosely refer to as colors. In order to measure light, we need an instrument that is sensitive to these colors. Our perception of light (using our eyes to measure it) is not linear. We are more sensitive to certain wavelengths than others.

In 1931, the CIE gathered a group of “standard” people and charted their “standard” response to light. About half way down on this page, you will find the CIE color chart.

Around 1964, CIE added another group of “standard” observers and made some corrections in the color chart. From what I can tell, this second group showed increased sensitivity in the blue to green range (400-520 nm), but the higher end remained the same.

This means that when we measure light, we are comparing what we see with what a “standard” group of people see.

In order to measure light, we need something that is sensitive to light, and a way to calibrate it to what we see.

This is where things get a bit dicey…

We all know that under different lighting conditions, colors appear different. In order to calibrate a light meter, there are Standard Illuminants set up that allow our meters to accurately measure the light under the calibrated Illuminant spectrum.

The Standard Illuminant A is set up to accurately measure the light from a blackbody source at a color temperature of 2856 K (very close to a tungsten lamp temperature). The spectrum of light changes with color temperature, so what do you think happens when you measure an LED with a color temperature of 6000 K with a meter calibrated to 2856 K? 

Ta-da… we end up with errors. It just so happens that a lot of light meters are calibrated to the Standard Illuminate A. I believe PeterW linked us to a video demonstrating this very thing in the Integration Sphere thread. In the video, the light meter was calibrated to a tungsten source, then used to measure other light sources and found to be off.

Light meters are cheaper than spectrometers, but they are only calibrated to a particular light source. Some meters allow you to choose between a couple of light sources. None, that I know of, have a setting for the light from LED’s.

If you are still with me, lets move over to this site and select the Calc button. Select CIE Spectral Display. In the Blackbody temperature box, enter 2856, then click the little box to the left and you should have a spectrum line on the graph. Now click on the A box (which represents the Standard Illuminate A), and notice the correlation between the two. The are in fact the same line.

Don is coming up to speed on using his spectrometer, and we are not sure if his numbers are totally correct, but he should be in the ball park. He has mentioned that the color temperature of a white LED is around 6100 K, and the color temperature of the SureFire A2 is around 3400 K.

Now let’s jump back to the calculator, leave the A box checked, and change the Blackbody temperature to 3400 K. You have to click on the graph to display the change. What started off as a perfect correlation between 2856 K and the Illuminate A, now is a bit off. 

Now, change the Blackbody temperature to 6100 K. How close are we now?

I have two light meters. Both are calibrated to the Standard Illuminant A. It will be interesting to see the difference between them.

By the way, Georges80 mentioned that according to the “experts,” it will be difficult to draw valid conclusions from the testing we are doing, because of the errors involved. I hope this exercise allows you to see where they are coming from.

Tom


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## McGizmo (Oct 8, 2005)

Hi guys,
Well I have some info and comments to add here. First for good measure though, a self induced .

OK, hopefully better now. :thinking:

I have sent off the SF A2, Aleph 1 UX1J LuxIII head and a blue K2 in Aleph 1 head to Tom. I got the following from these lights:







I didn't put in a CCT for the blue but it was 0 for those interested! :green: I have no idea how far from reality these absolute values are but the relative comparisons are legit AFAIK. One note of interest is when you consider that the white Luxeons are actually blue luxeons with phosphor added. Obviously flux and lux measures don't tell the power story but if you look at the mW measured, you can see that the blue K2 is in fact putting out more power than the white LuxIII but in a band that is discounted significantly due to its relative poor receptivity with the human eye; per CIE and that stuff Tom is talking about.

Now I have the following meters, Meterman LM631, Lutron LX-102 and a recently acquired Extech EZ view 30. I noticed in the manual for the Extech there is a relative response graph of the spectrum based on CIE and the light meter's response is a trace of this curve with the exception that it drops about straight down at just under 500 nm whereas the CIE response slopes down to nil at about 425 nm. In the CIE case, the relative response or sensitivity is down to about 25% at about 500 nm but it is clear that the Extech is going to miss some power in the blue hump of the white LED wheras the eye will not miss this. The blue K2 may proove to be the most telling LED here for our meter's abilities to measure the "blue bump" !! From my measurements below, I think this is rather clear:






Notice that both the Extech and Lutron were rather blind to the blue K2! It would seem that lux and lumens measure ignore the blues and some of these meters are even more oblivious! However, with LED's it is a mistake to ignore these bands of light. For consideration, visualize a nice bell curve that peaks at 550 nm and drops to about 20% in relative response at 480 nm and then again at about 630 nm. This curve is the CIE curve and some of these meters likely can handle the longer wave lengths in relative comparisons to our eye's sensitivity but it would seem that the shorter wave lengths will not be well represented or counted. :shrug:

OK, this is my input and now the ball is passed on with one final comment:

This project turned out to be very illuminating for me in a very unexpected and upsetting manner! I decided to glue the reflectors and light engines in place with Arctic Silver epoxy to keep them in the same configuration for the duration. Whenever one "fixes" components in place, it is an invitation for Murphy to climb on board; this is a given!! Well I knew that but figured so what! We will all be measuring the same source and this should be the case.

However, after looking at the lux measures of this powerful UX1J behind the 27 mm reflector, I knew something was goofy! I had noticed that the spot was rather smooth and not sharp but didn't give it any thought. Well, the LuxIII in this CPF standard is of the new packaging which has been briefly mentioned but not really explored to my knowledge; or at least really delved into here on CPF. To date, I have only used the new style LED's, to my knowledge, in my HD45 and very recently, some U bins in some PD's of color. I am now aware of the fact that these LED's do in fact have an image location different than their predecessors and focal allignment is not the same!!!  I have attributed the less than stellar lux measures of the HD45 to the orange peel of the reflector when it now seems that a possibly stronger influence is the fact that the reflector is in effect forward of the focal point by probably .015" to .020" at a guess. Ironically, I have been trying to design and effect optics which cause the beem to diverge more and get more light in the corona and it seems that Lumiled's, in their infinite wisdom has implimented a push in the same direction without any alert to us lowly customers! The good news to flood lovers and white wall hunters is that at least in the case of the lights I have been making, the beam will not disappoint nor does it look bad. However, if you are in fact looking for high lux measurements and long throw, these new LED's will require modifications to optics designed for the previous packaging and/ or placement changes within their hosts! WTF!!!

I have been sitting on this post while I did a quick build and light test. I put one of the new version (we need a friggin name for these damn things!) Luxeon's (UX1K) in a Light Engine with DB917 driver. I put the LE in an Aleph 2 head with stock reflector and no window and put it in the integrating sphere as well as took a lux measurement with it. 80 lumens and a lux of 1030. I then took this same reflector and faced .015 off the rear of the reflector and put it back with the same LE and again took flux and lux measures. 80 lumens once again but the lux jumped up to 1525. There was essentially an increase of 50% in the lux measure! There is no loss of photons but the deployment is certainly effected! 

A quick and late query to the Future Reps I have been in contact with resulted in a comment of essentially, news to them! I suspect that there is going to be mixed inventory coming down the pike in production units and some manufacturers may catch wind of something not quite right or the same from customers who may notice something "off" about the lights. :shrug: In addition to the fun lottery, Lumileds it would seem has added blind siding of the customers as an additional bonus and part of the game.


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## wquiles (Oct 8, 2005)

I specially like how nice the A2's spectrum looks like compared to the LED's. I am also shocked at the difference in lux from the new style LED's which have a different focal point - neat to see that (as expected) the total lumens were the same. I am one of those (few?) that preffer the flood vs. the pure trow, so for me the new LED's should be great!

Awesome data Don :goodjob:

Will


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## rdshores (Oct 8, 2005)

The change in die height was discussed here a while ago when the slug shape went from oval to round. I've just spent over an hour trying to find the link, but I have given up. Either I don't know how to search, or the search funtion sucks. I don't see anyway to search the archives. I even use google to try and find CPF links sometimes. If anyone finds the thread, please post a link. Thanks.


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## wptski (Oct 8, 2005)

You all know that a MeterMan LM631 is the same as a Extech 403125 although there is a Extech NIST version too!

http://www.extech.com/instrument/products/400_450/403125.html


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## wquiles (Oct 8, 2005)

rdshores said:


> The change in die height was discussed here a while ago when the slug shape went from oval to round. I've just spent over an hour trying to find the link, but I have given up. Either I don't know how to search, or the search funtion sucks. I don't see anyway to search the archives. I even use google to try and find CPF links sometimes. If anyone finds the thread, please post a link. Thanks.



Linkie as requested: Luxeon5 slug bottom shape has changed to round!  

Will


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## McGizmo (Oct 8, 2005)

Hi guys,
The new "joker" Luxeon is not inherently a more floody LED it is just that in installing it in a system designed for the previous LED results in a floody result. You can simulate the results with a previous version LED by shimming the reflector up about .015" away from the LED. This has been a method I have used with 5W LED's to diminish the projection of the "null". 

The linked thread on the slug of the 5W is not the same thread where pictures were shown of the LuxIII Joker and the obvious new position of the die. I caught that thread, thought Uh Oh and then there was a follow up of images of reasonable beam shots with the joker and I figured perhaps the bullet had been dodged. I had a funky gut feeling but with a full plate and not dealing with jokers at the time, I personally left my head in the warm comfortable sand! :green:

Do we even know if the new 5W has a lowered die?

Regarding the meters, I noticed that Extech also has a meter that is a spitting image of my LX-102. :shrug:

On a personal note, even though I don't know the level of error in my integrating sphere, the ability to get relative flux measurements along with the lux measurements is really helpful in comparing changes in geometry of the assembly as well as evaluating different components, like this joker!! By lux measure alone, it is very difficult to gauge the power of the light going out the front end.

* EDIT: I wanted to mention that although I prefer using the Extech meter over the others due in part that it is EZ to See (  ), and the fact that I use the LX-102 coupled with my Fluke 189 for run time tests, I know feel that the Meterman is the most "appropriate" meter of the three in use with the LED's. If my flux mesures in the IS are reasonable, you have 51 lumens for the LuxIII white joker and 12 lumens for the blue (23.5 % of the joker). If you take 23.5% of the joker's flux reading from the Meterman: .235x1130=265

Well the measure of 345 is much closer to 265 than the 85 lux measured by the LX102 or EZ30. It would seem that the Meterman has a sensitivity that is more inline with the full CIE response curve and not truncated in the blues as are these other meters. :shrug: *


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## SilverFox (Oct 8, 2005)

Hello Don,

Interesting results...

One question comes to mind:

If the Extech meter (EA30 by the way) is less sensitive to blue,
and the White LED has a significant blue spectrum,
then why does it show a similar reading to the Meterman when measuring the white LED?

Any thoughts on this?

Tom


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## McGizmo (Oct 8, 2005)

Tom,
as we discussed on the phone, I am clueless and guessing here! :nana:
I am suspicious that some methods of measure, even though weighted by the CIT curve, *see* an aggregation of light in its whole and not its spectral constituants. Idle speculation on my part and I have to get out of idle and back to work so, :wave:


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## SilverFox (Oct 8, 2005)

Hello Don,

I just did a very rough comparison of 3 of the $1 key chain lights.

My cheap meter was in good agreement with the Extech EA30 on the white LED, but the cheap meter read higher for both the blue and red LED's.

For everyone else, my reference to my cheap meter simply means that it is one I got off eBay when a high school was upgrading to the metric system. It only measures foot candles and it cost me $5 + $2 shipping. Thus it was cheap. This reference refers to the price and has nothing to do with the quality or ability of the meter to measure light.

Tom


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## rdshores (Oct 8, 2005)

Thanks for the link, but that is not the one I had in mind. The one I remember had a picture of the old and the new together with a line drawn across both to show the difference in die height. It also had a link to LUMILEDS data sheet mentioning this change.


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## McGizmo (Oct 8, 2005)

Tom,
That does it! 

I will build an Aleph 1 with a red K2 today and get it in the mail to you. It will also be driven by a NexGen500 and I just tested the Vf at 500 mA and measured 3.1V on the bench supply. The fact that the red K2's have such high Vf's will allow them to be driven in regulation by a boost driver on a CR123. If folks test the red last after the white and blue, their CR123 will be below the Vf + overhead of the NexGen.


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## evan9162 (Oct 8, 2005)

So we're now testing Red, White, and Blue lights?


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## SilverFox (Oct 8, 2005)

Hello Evan,

It gets better than that.

Just had a discussion with Don. He has decided to throw in a green one too.

I have edited the first post to reflect the changes.

We will have 4 heads for the LED light. White, blue, green, and red. In addition we will have the SureFire A2 incandescent.

Don suggested that we test the red LED last because of Vf characteristics will allow it to stay in regulation longer on a used battery. We will have a conservative 40 minutes of regulated run time. I think we can do that on 1 battery, but you can always steal the batteries from the A2 (after you have tested it, of course) if you find yourself taking a bit more time conducting the tests.

Tom


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## georges80 (Oct 8, 2005)

evan9162 said:


> So we're now testing Red, White, and Blue lights?



Yes, this is the whole point of what the Sphereoptics guy (Chris) was saying when he visited with me on Wednesday. The existing light meters that measure Lux etc are photopic in response are pretty hopeless in reading anything other than something like a tungsten light. They are designed to provide a reasonably accurate reading that would mean something to our eyes (photopic response). But, since our eyes aren't particularly sensitive to the low or high end of the spectrum, the meters don't have to be too accurate at those ends. Now, enter an LED that 'makes' white light by mixing different spectral components that have peaks (refer to the spectral shape of a Luxeon white LED) all over the place. Some of those peaks are where the meter isn't particularly accurate - so the final "lux" reading is way off unit to unit.

So, Sphereoptics' point is that using a Lux meter is pretty useless for LED measurements since the areas of interest in the measurement are most likely in the area that the Lux meter's response is pretty lousy, especially meter to meter.

That's why in my previous comment above I mentioned it would be interesting to add in different binned Luxeons. Don's idea to include a blue & red LED is good - since they are at reasonable extremes of the spectrum and will provide us a way to confirm Sphereoptics' claim that Lux meters are not good instruments to measure and specify LED performance.

george.


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## evan9162 (Oct 8, 2005)

Nice! Now we'll know how our meters match up in different parts of the spectrum. 

It'll also give me an answer to another quandry I had. I've done the lumen integration technique with a red-orange Lux-III, and got some interesting numbers - while so far, my technique has resulted in numbers lower than expected, the R-O test resulted in higher than expected numbers. 

It'll be nice to know if my angular lumen integration technique has any merit whatsoever...


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## SilverFox (Oct 8, 2005)

Hello Don,

We need to come up with a value for this whole package.

When we ship, how much should we insure the package for?

Tom


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## McGizmo (Oct 8, 2005)

Tom,
Like the MasterCard, it's priceless! :nana:

If I were to build these again as replacements, I would want the normal build price on an Aleph 1 head which is $125 and there are to be 4 of them?!? Granted, the LED's used are not typically available at present but there is also a good chance that the Aleph 1 heads are all gone by some time that replacements would be needed. So although these were "free" like the local pusher, the "next" set would cost!!  I don't know the going price on the SF A2 but perhaps if the lot were insured for $500, that would keep the various carriers honest?

GeorgeS80, I can understand where the light experts are coming from but on the other hand, do they suggest that these lights with their collimation systems do not get measured for lux or do they propose some other method like simply flux? We know how useless flux is in terms of illuminating a distant target! Perhaps Chris at sphereoptics would like to measure these samples and give us the "true" measure of their outputs! 

I take it on faith that flux and lux are based on the CIE standard. I also take it on faith that our tools are based to some degree on the same CIE curve. However, I also take it as a given that the light sources we use are not based on the CIE nor to some unknown extent are my old and tired eyeballs! If I can come up with a scheme to put repeatable numbers to what I touch and see as a means of quantifying what I work with and see, then I am game and let the units of measure be Berkely Bunkoids for all I care! 

BTW, before I forget, all of the Aleph 1 heads have sapphire windows which are not the most efficient for light transmission but they will not be likely to chip or break on us. You can also clean them without scratching them or any AR coating which could skew the readings (like we have sensitive enough equipment to catch this!  )


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## Kiessling (Oct 8, 2005)

IMHO we would not want to re-invent the perfect method to measure light but simply aim for a way to calibrate our crude measuring instruments (light-meters) so that we obtain reliable and valid measurements within the group, meaning some intern validation.
Of course there will be errors, but the question is how far do we go costwise and effort investment wise to correct external errors of the absolute values obtained?
I think there should be a line to be drawn, and this line should represent a frontier where the invested effort isn't worth the returns.
bernie


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## evan9162 (Oct 8, 2005)

Are we going to start a new thread so people can post their results?


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## SilverFox (Oct 8, 2005)

Hello Bernie,

The other side of this comes into play when you have a light that measures 3500 lux and I have the same light (but a different meter) that shows 3300 lux. If we find out that the actual light is at 3400 lux, we can rest assured that we are both looking at the same light.

While reviewing lights, we place a lot of weight on the importance of throw. This testing may reveal that, while throw is still very important, we need to take our actual measured lux readings as something less than absolute.

Please keep in mind that one of my goals in this testing is to find out why my Aleph 3 has more throw than yours. You have reported around 4900 lux for yours, and I am looking at over 8000 lux with mine.

Darell built my Aleph 3, and while I know he is very talented, I think he put a little magic dust in mine...  

Tom


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## SilverFox (Oct 8, 2005)

Hello Evan,

We will be posting our results in this thread. I will keep track of things in a spreadsheet.

We may be able to get Brock or another Administrator to put the spreadsheet up in a locked sticky.

While the actual results are very important, I also believe that the process is also important. I would like people to feel free to discuss their set up and observations and this is a good thread to do that in. We can also address the questions and concerns that will come up.

When the testing is complete, we can then list the results as a reference and list a link to this thread for those who are interested in how we came up with the values. As a reference, I think it should stand on its own and not be diluted down with a lot of discussion.

As always, I am open to any discussion on this... Comments?

Tom


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## SilverFox (Oct 8, 2005)

Update:

The first post has been edited to reflect the insurance value of $500 for these benchmarking lamps.

Tom


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## McGizmo (Oct 8, 2005)

Hi guys,
I got the green and red Aleph 1 heads built and introduced them to the integrating sphere and my three meters. Having these colors to look at will definitely give us all more food for thought!!







For the lux measurements:

Light------------LM631---------LX102----------EV30
RED-K2----------866------------1495-----------1665
Green LuxIII------2820-----------2570-----------2580

So it would seem that the meterman is more interested in the blue end and less in the red in comparison to the other two meters. The green LED scores highest in lumens and flux of all of the LED's as well as lowest in radiometric power measured. :thinking:

For those who haven't visited the "Color of Light" thread, I bring a couple spectrums over to consider in terms of the CIE standard as well as the sensitivities of these meters as compared to our eyes.






Yet our eyes receptors in the cones consist of 3 types of receptors who's relative sensitivities are expressed:






and






It would seem that we are more sensitive to the blue, say 450 nm band than some of our meters give credit to and in fact that which the photopic vision gives credit to?!?! Now the scotopic or night adapted vision does seem to be very sensitive to the blue and yet we use red light for night vision to what, keep from over exciting our blue receptors? Is it possible that with very low levels of blue light, we can retain our night vision and actually see well as well? :thinking: Are the blue receptors there for navigation by moonlight? Some of us try to bring sunlight to the night and perhaps this is the cam who feels that you can't have enough light. Others of us just want to bring the minimum needed to bear and perhaps it is this group that prefers the HID tint and are perhaps subconciously trying to bring more moonlight to bear. I think I am in the second group. 

It is interesting to me that in scotopic vision, red is not part of the program at all! So it's then OK to flood the field with red?!?! By the same token, I know that I have been out in the dark and somewhat adapted, at least to low levels of photopic vision and when I fire up a Royal Blue LED, I find the visual impact very unsettling! Cyan on the other hand, is more pleasing and I wonder if this is because it falls in a slump among all three receptors. :shrug: 

The cool things with these LED's is we aren't limited to the broad band of black bodies! :nana:


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## HarryN (Oct 9, 2005)

Pretty facinating work Don - and thank you very much for your efforts and generosity on this project. Same for you Tom.

I remember a thread related to a boosted Thor that Newbie was playing around with, and he had to go to some effort to separate the IR output of that bulb to from the visible measurements on his Lux meter. Any idea how much of the Lux or Lumen measurements from the A2 are coming from the "non visible" (nominally above 650nm with my eyes) wavelengths ? 

I guess in theory, these are corrected to remove the IR part - right ?


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## SilverFox (Oct 9, 2005)

Hello Don,

:thinking: :thinking: :thinking: 

By the way, what is the temperature in your closet?

I am not sure changes in temperature during our measurements are going to amount to much of a deviation in our readings, but we might as well keep track of it.

Tom


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## SilverFox (Oct 9, 2005)

Hello Harry,

I just took a very powerful IR illuminator and checked it on the Extech EA30. At 1 meter, it is reading 0.86 lux.

That suggest to me that the meter is filtering out the IR pretty well.

Tom


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## SilverFox (Oct 9, 2005)

Hello again Harry,

I just checked out my DFC-100 (the cheap meter) and it is showing 40.5 lux, at 1 meter, with the same IR illuminator.

This meter does not seem to have as good an IR filter...

Tom


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## McGizmo (Oct 9, 2005)

Harry,
According to the data bullets on these meters, they follow the CIE sensitivity curve so the IR should not be getting factored in. The one graph with the EZ30 shows the CIE curve and the meter's curve which are the same with the exception of the EZ30 dropping off on the blue side. The red or IR side is the same curve. The Meterman certainly doesn't seem to be overly sensitive to the reds and perhaps is a bit too conservative? I had already sent the white sample on to Tom but it may well be that in some actual distant target acquisitions, the red may be seen to be on parity if not more intense than the white as the lux measures seem to imply. The red die is small and since it is more in focal allignment with the 27 mm reflector than the white, lux readings may agree with emphirical investigations. :shrug:

It would be informative to have the CIE curve placed over these other spectrums to see how flux and lux measures are *supposed* to be adjusted.

*EDIT: ambient temp was mid 70's (F) *


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## gadget_lover (Oct 9, 2005)

McGizmo said:


> It would seem that we are more sensitive to the blue, say 450 nm band than some of our meters give credit to and in fact that which the photopic vision gives credit to?!?! Now the scotopic or night adapted vision does seem to be very sensitive to the blue and yet we use red light for night vision to what, keep from over exciting our blue receptors?




Yes, that's exactly it. I read something about the way a chemical in the receptors is depleted by exposure to light. Using a red light registers with the photopic vision and does not register with the scotopic or night adapted vision at all. 

Daniel


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## SilverFox (Oct 9, 2005)

Hello Don,

I was playing with your numbers and looking at the chart for Scotopic and Photopic spectrums.

Your green LED numbers suggest a value of 542 lm/watt. The Photopic chart shows that at 555 nm, they are getting 683 lm/watt. Since the LED that we are measuring is a bit below that, it looks like the 542 lm/watt figure should match the curve within reason.

Your blue LED is coming in at around 48 lm/watt and also seems close to fitting the photopic curve.

Your red LED at 151 lm/watt also seems to be close to fitting the photopic curve.

I have no idea what all of this means, :nana: but found it ineresting...  

Tom


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## HarryN (Oct 9, 2005)

The green numbers having a lower radiometric and high Lumens relative to the other colors actually makes a lot of sense. The green is more easily "seen" due to the nature of our eyes, but it is the most difficult LED color to make. (one of the reasons that a green LED of similar brightness is more expensive)

For those interested, the green ones require the incorporation of "activated" Indium into the GaN matrix. Since the Indium atom is so large compared to the Ga and N atoms, it is a difficult fit. Sort of like trying to put Moby **** in a bath tub.


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## McGizmo (Oct 9, 2005)

Hi guys,
I am finding all of this very facinating and thought provoking. I should emphasize that my IS and spectrometer are likely "close" in terms of calibration but the numbers are not to be taken as hard. I do hope to get my own calibration source that is consistant with how I am presenting these lights to the system and then the numbers should be available with a reduction in current error levels. 

One number which I used to think I had a feel for was the CCT and perhaps my perception of this number is appropriate for a black body lamp but I think it is misleading as heck for LED's and their tints! I don't know if it is due to a cammel hump being represented by a single hump or what. :shrug: Perhaps my system is just putting out garbage numbers here?!?!? The UX1J LED is on what I would consider the warmish tint and look at the CCT number for it and certainly the CCT number for the green LED!!! :green: WTF?!?!

Well I just did a google on "CCT light" and found a brief explaination and the graph below, HERE.







Obviously, black body sources do not give off green and so to assign a CCT to a green light source is kind of silly! The more I explore this stuff and hear the rumblings from the experts, the clearer it is that the LED's will require a new approach in terms of quantifying and describing the resultant light emitted. I find it interesting that we have a tripple peak spectral sensitivity which now responds to a double peak spectrum from LED lights but our measuring system is based on a weighted single peak spectral curve. 

From some simple exploration with the white LED's I have come to think that the tint from them is as much if not more a result of the relative heights of the two humps as much as any wave length shift of the peaks of these humps. My spectrum software has a ratio that I can set which puts the power of one user selected nm band width over another user selected band width. Forinstance I could set this ratio measure at (425 to 475 nm) /
(525 to 575 nm). I suspect that this ratio could be a number mapped to perceived tints of the LED's and be more in line with predicting or effective in assigning a tint to a number. Essentially this would be a relative power ratio of the blue hump over the green/yellow hump. It may be that the industry is providing accurate tint binning information based on inappropriate methods of measure? So much of what I read is based on black body and these LED's are playing by a different set of rules!! There seem to be some "ethnocentric" errors in understanding here and I guess lux and flux themselves have a basis that is faulty for these sources of light?

In doing some google, I found a couple interesting sites:

On this "calculator", you set three points but two of them can be the same point or the three points in line with eachother:
Chromaticity diagram "calculator"

CIE Color System this is a great site!!!

On the calculator above, if you pick the three peak bands of our receptors, say 450, 540 and 580 and select these points along the edge of the diagram corresponding to the wave number and then slide the bars below to give relative intensity weighting to the three receptors, you can see that the resulting color is that in the cyan tint. Now as I understand this, a proportional stimulation of our eyes with a dark blue, green and red/yellow source of light will result in the perception of a cyan color. However if a single and tight band of cyan light is presented to our eyes, we will not perceive this light in its true intensity as this is a band that is not related to any of our receptor's peak sensitivities?!? :thinking:


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## HarryN (Oct 9, 2005)

Hi Don - I have attended quite a few seminars on LEDs, Chromaticity diagrams, CIE, etc. Just to make you feel better, the people that study light for a living are still arguing about the same aspects of "what they see" and "does it matter".

It is useful to view these charts for what they really are - They are an engineering attempt to mathematically approximate how to fool your eyes into thinking they see "something". A material scientist would call it a phase diagram of color vision. Keeping in mind it represents the vision of Scandinavian college students IIRC, it is somewhat telling on why Fuji tends to make its films "warm" and Kodak make its film more "cool".

As you have observed, you can use the CIE diagrams to select three different wavelengths, mix them in various portions, and end up with a mixture which will "fool" your eyes into thinking you see a particular X/Y coordinate or CCT. That is quite different than the blackbody emission your eyes and brain are designed to assume.

You can also do the same thing with only 2 wavelengths (such as 490 and 620 nm) to make a very high color temperature white (11,000 K) I have done this, both on the charts and in real life, and it does in fact look really neat on a white wall, but the lack of certain colors quickly shows up when you shine it on an object which is blue or purple - they look a funny black color. (no, I am not kidding - the color looks like a strange black - not normal black) BTW, the motivation for doing this is that it is REALLY efficient.

At the opposite end of the attempt to "fool" your eyes, you can mix 100 different wavelengths together (not with that calculator, but it can be done) and obtain a light which is very vibrant and rich in color on almost any object. NIST has a unit like this under development to become their new "transfer standard", with LED wavelengths every 2 - 5nm (cannot remember exactly). They consider this to be supperior to the current standard sources for a variety of reasons.

Since it is difficult to pack 100 LEDs into a flashlight, LED makers use various phos mixtures to "fool your eyes" into thinking they see white. For each emitted wavelength, the colors look more realistic, and the efficiency drops. A good example is to compare the very wide output of the LL "warm white" Lux I against a standard "cool white" Lux I. The warm white has virtually all of the colors of an incan at approx 3300 K, but none of the IR. The downside - about 1/ 2 the lumens of the Lux I. The "tints" that we all love to micro analyze are just the natural result of very slight changes in the blue starting point wavelength (as in 2 - 5 nm) and slight variations in the phos mix, and I do mean slight.

As you see, your meter and eyes are very good at picking up these slight variations, even though they actually represent only a few atomic layers of variation.


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## Bullzeyebill (Oct 10, 2005)

I checked USPS web site. Insurance fee for $500.00 value will be $6.20. Not sure what fee for total package, Priority, confirmed, + insurance. Probably around $11.00, maybe less. This project is well worth it. It would cost much more to have my LM631 calibrated.

Bill


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## PeterW (Oct 11, 2005)

Good links!! I am in the process of getting up to speed with this for my job. The colour temp can either be the best fitting black body curve to the source spectrum or the colour temperature on the blackbody curve that is closest to your source in CIE colour space.

You will get an error in the sphere with different beam distributions due to the differing inter reflections and also from a different source. Different LED/holder combinations will absorb a different amout of light.... big spheres have another source to correct this out. Sphere==can of worms! (But a fun one as you are discovering.... I'd quite like one to play about with too!)

Cheers

PeterW


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## SilverFox (Oct 11, 2005)

* CAUTION *

I do NOT recommend doing this. It is possible to damage your light meter or possibly throw it out of calibration by doing this...

However, I was curious.  

My Extech EA30 EZView light meter is advertised as having a "Photopic" filter to insure "accurate" response.

Since Don has demonstrated a different sensitivity to the blue LED, and I found a difference in the red and infrared end of the spectrum, I got to thinking that perhaps this difference could be attributed to the Photopic filter.

I took my light meter sensor casings apart and here is what I found:






Here is a closer look at the sensors:






Other than the size difference in the silicon photo diode, notice that the EA30 has a greenish filter over it. The other meter sensor has no filter at all.

I believe greenish is towards the middle of the spectrum. Does that mean that by using a green filter, you attenuate both ends of the spectrum?

I found a spectrum sensitivity for a photo diode and it appeared to be a sloped straight line that looks very similar to the middle part of the spectrum Don displayed for the A2. Adding a filter will shape the light response and I believe it makes it fit the 2856 K curve better. 

At any rate, I can say that my meter with a Photopic filter is less sensitive to red, blue, and infrared, than my meter without. I don't think you can draw a lot from that, it would help if both meters were the same manufacturer, but I found it interesting never the less.

Tom


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## js (Oct 12, 2005)

Don et alia,

Staggeringly good posts! Awesome! I love it. Especially the lumens and CCT info on the A2--and, yes, I understand that there is no guarantee that the 79 lumens is absolutely accurate, BUT, I know that Peter Gransee had a number of lights tested in a professional integrating sphere, including the E2e. The E2e measured out at 83 lumens (presumably on fresh batteries, IIRC), and I can't see much difference in total output between the E2e and the A2, when the E2e has fresh or nearly fresh batteries, so 79 lumens sounds just right to me. The CCT is definitely right where I expected it to be. I would have guessed 3300 (Tom can vouch for me on this), and there it is at 3313. Neat! Using the known efficiency of a halogen at 3330 (30 l/w) and my guess of the power of the A2 lamp (5 watts), together with a 50 percent loss rate in the reflector (LED holes bring it down from the standard 65 percent), yields 75 lumens.

So it all hangs together surprisingly well. Who needs to spend $20K? Just apply a liberal does of common sense, add some genius and determination (Tom and Don), and VOILA! you have a pretty good back of the envelope stab at reasonably accurate absolute numbers.

<muttering to self> I always knew the A2 put out more than 50 lumens!<end muttering>


And Don, you absolutely MUST stop following such posts with "I'm stupid." If _*you're*_ stupid I really hate to think what the rest of us are. Color me sub-moron.


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## SilverFox (Oct 12, 2005)

Update:

Since Monday was a postal holiday, things got slowed down a bit.

I just received two packages from Don today... The benchmarking lamps are here.

Tom


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## SilverFox (Oct 13, 2005)

Update: 

I have started a graph of the meter testing results in the first post of this thread. I will try to keep it updated as the testing continues.

I have two light meters. One I got off eBay for $5. I do not know the manufacturer, but the model is DCF-100. The other meter is an Extech EZView EA30.

The DCF-100 measures in foot candles, so I took my measurements at 36" and then normalized them to 12". Since foot candles at 1 foot = lux at 1 meter, I am simply reporting these numbers as lux at 1 meter.

My light measuring set up is portable. I took three measurements on each light with each meter, and moved the meter to a different location for each set of measurements. I set things up, took measurements from each light, then moved to another location. I am pleased that the scatter in my numbers is minimal.

Of the two meters, I trust the EA30, but I am not sure what to make of some of the numbers. I know the EA30 is less sensitive to blue (calibration documentation) and infrared (actual testing with an IR illuminator) than the other meter.

The test temperature was 70 F.

Here is what I came up with:

DFC-100
A2 Incandescent - 2448, 2412, 2439 for an average of 2433.
White LED - 1044, 1035, 1017, for an average of 1032.
Blue LED - 1215, 1233, 1251, for an average of 1233.
Green LED - 1596, 1566, 1584, for an average of 1582.
Red LED - 1538, 1511, 1502, for an average of 1517.

EA30
A2 Incandescent – 2562, 2497, 2570, for an average of 2543.
White LED – 1186, 1190, 1195, for an average of 1190.
Blue LED – 63, 64, 65, for an average of 64.
Green LED – 2602, 2584, 2593, for an average of 2593.
Red LED – 1760, 1770, 1768, for an average of 1766.

Tom


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## evan9162 (Oct 13, 2005)

Tom,

Nice first set of data! Interesting how the incan and white LED measurements were pretty close, but the blue/green tests were WAY off! Looks like this is going to be a very informative test!


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## Kiessling (Oct 13, 2005)

oo:
I guess this project will turn out to be even more useful than we might have imagined ...

BTW ... is there a consensus about the few intl. participants yet? Do we ship our light-meters to you or not?

bernie


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## SilverFox (Oct 13, 2005)

Hello Evan,

Yes, very interesting...

It is too early to draw any conclusions, but there may be a hint of a suggestion that white light may be more than the sum of its red, green, and blue components...

Tom


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## SilverFox (Oct 13, 2005)

Hello Bernie,

I was going to wait a little bit longer to see if any more international people were interested in this.

As it stands right now, it probably would be better to have the international people send their light meters state side for comparison.

Tom


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## SilverFox (Oct 13, 2005)

I am sure some of you are wondering about the lights we are using for our benchmark light meter testing.

Here are a few pictures of them…









































Tom


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## SilverFox (Oct 14, 2005)

Craig (The LED Museum) and I got together today to ogle over the CPF Standard Light Meter testing lights, and to check out his light meter.

Funny thing, the Thor reflector will blind you when you shine a light into it in a dark room...  

Craig has the Meterman LM 631 and the temperature was 77.2 F.

A2 Incandescent - 2150 lux at 1 meter
White LED - 1000
Blue LED - 190
Green LED - 2080
Red LED - 1070

We tried several measurements, and they came up the same each time. I guess we are pretty good at setting things up.

I will update the graph on the first post to reflect these measurements shortly.

Tom


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## NewBie (Oct 15, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

If you think a little harder, why the red light...

Your rods (night vision), have no response in the red end. However, they are 10,000 times more responsive than cones, and can see somewhere between one single photon and nine photons, depending on which school of thought.

Thus you can use red light, which uses the cones, and then switch to looking around, using your night vision, with no interference- no loss of night vision.

Rods are extremely slow to adapt, and enough light in the rod response frequency to navigate decently, thrashes your night vision in the rods.

Another interesting point for folks. Rods sparsely populated in the center of the eye, and are dense in areas other than the central area. They are very sensitive to changes, and being extremely sensitive once adapted, they are awesome for detecting movement. Trained night observers do not look directly at the subject they are looking at, but off to the side, in order to utilize the rods more effectively.

Cones are dense in the central region of the eye, but are very poor for night vision. They also rapidly adapt to changing light conditions, unlike rods. But they are also much slower in their response to slight changes, such as is used to detect movement, where the rods excell.

Another reason for the red light, besides not disturbing your night vision, is that the red cones are quite plentiful in the central region, and you can see details extremely well. Where with the 30 minute adapted night vision, the rods are very sparse in the center, making it quite hard to do things, especially reading.


The spectral response of typical light meters is very bad, as I have long mentioned, for well over a year. Some meters have correction factors you need to multiply the results for (or fancy ones have a switch), depending on incand/mercury/sodium/fluorescent light sources, since their spectrums are "known", it is easy to correct for. As a point of reference, fluorescent lamps are not close to LED spectral responses.

In the display industry, they are a no-no, as with other light sources, such as HID and LEDs, they are highly inaccurate, and can easily be off by a factor of 50%. This is where spectroradiometers with linear CCD arrays and diffraction gratings come in.

Anyhow, seems like a fun deal folks have going on in this thread, enjoy!


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## SilverFox (Oct 16, 2005)

Update:

I became aware of some problems with the Titanium 123 cells fitting in the A2. I have done some testing and found that the old Titanium cells do not fit, however the new individual cells do.

The new Titanium cells have "PTC Protection" on the label.

AmondoTech also offerers the new Titanium cells in a two pack with heat shrink holding the cells together. These two cell batteries are intended for a two cell light application. These two cell batteries also will not fit in the A2, until you remove the heat shrink that is holding to two cells together. As I mentioned before, the single cells will have no problems fitting in the A2.

I check a number of other cells and have had no other problems. The BatteryStation cells are snug, but still work OK.

Tom


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## SilverFox (Oct 17, 2005)

Update:

I mailed the lights to Bill Waites today. There are boxed in a USPS priority mail box without batteries. The total weight is 14 oz.

Cost for postage - $3.85
Cost for $500 insurance - $6.20

Total - $10.05

Tom


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## andrewwynn (Oct 18, 2005)

oops.. i posted in the wrong thread.

-awr


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## js (Oct 18, 2005)

andrewwynn said:


> I'll have to get my hands on one.. if the nano ckt fits inside it could be a really neat mod for folks to attempt themselves.. if they can make a 'knockoff' nano for 1/2 price.. pretty cool. (lotta work.. but cool).
> 
> -awr



Andrew,

Hello? Hello? Do you know where you are? This is a thread about bench marking CPF lightmeters via some CPF standard sources. What are you talking about? Did I miss something earlier on about a mod?


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## NewBie (Oct 19, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



js said:


> Andrew,
> 
> Hello? Hello? Do you know where you are? This is a thread about bench marking CPF lightmeters via some CPF standard sources. What are you talking about? Did I miss something earlier on about a mod?




Oh good, it wasn't that I was just too tired and couldn't follow what the relationship was to this thread. That one had me scratching my head for a little bit the other day!


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## bwaites (Oct 19, 2005)

The lights arrived today, A2's look funny without cells in them!!

I'll get and post results tonite if all goes well. I'm waiting to put together a few more USL's until the switches set a little better.

Bill


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## SilverFox (Oct 20, 2005)

Update:

I got a call from Bill last night. It seams he is expanding the standard deviation with some of his measurements... 

He reported
A2 2260	
White LED 991
Blue LED 1177
Green LED 1525
Red LED 2580
and a test temperature of 71 F.

He took the measurements several times and came up with the same numbers. I will let him add any other comments he has.

I have added his numbers to the graph and added a spread sheet showing averages and standard deviations... Some of the standard deviations are quite high.

I have also added the list of people who have signed up.

It looks like Sigman is next on the list.

Tom


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## Codeman (Oct 20, 2005)

Tom,

If you don't mind, please go ahead and add me to the list. By the time it gets to me, work should be calmed down enough that I can test and ship it quickly.

Thanks,
Ray


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## McGizmo (Oct 20, 2005)

Interesting! At the moment, we have a greater deviation on the incan than the white LED. :thinking:


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## bwaites (Oct 20, 2005)

This was one of the most frustrating things I have ever done with flashlights!!

I started by setting up a the test per the protocol with the variants I usually test with.

1 Meter measurements using a Meterman LM631.

Light meter placed in the center of a large matte white posterboard, 30 inches by 24 inches which completely encompasses the hot spot and most of the spill at 1 meter for focused LED's. 

Placed on a matte, taupe colored wall at 45 inches above the floor, 9 foot ceiling height.

Lights secured on a camera tripod and then moved until the hottest part of the beam is found.

I measured without reviewing the previous measurements, but I've measured A2's enough to know that they average around 2300 +/- 200 lux. 

I did the measurements, then reviewed the others done so far. 

I was SO flabbergasted at the differences in the colored LED's that I went back and repeated the measurements!

The numbers are what they are, and after discussion about the findings with Jim Sexton and Tom, I remain flummoxed by the differences in the colored LED's!! Obviously, the white/yellow colors are well controlled in the meters, the error between my readings and LED museums are well within acceptable error ranges, but...

The colored LEDs are WAY out there and I am now interested in seeing the rest of the results even more.

There is one fun experiment to do after you finish the measurements, if you have a few extra ALEPH tubes or power supplies:

Try to arrange the colored LEDs so that the output on a surface is roughly equal and the hot spots overlap. See how close you can get to white by moving each LED closer and further away. (Hint: The red remains stationary, the other two should be closer than the red.)

Have fun!

Sigman, PM sent.

Bill


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## Codeman (Oct 20, 2005)

Don't forget that light meters, at least most of the ones we use on CPF, are calibrated to measure daylight, or something close to it. I would expect white LED's to give at least slightly invalid results to start with, and the colored ones even more skewed.

I suspect the colored ones will end up showing larger deviations after we've got a reasonably large sample size of different meter brands than the white sources. We'll probably see that the farther from daylight a particular source is, the wilder the measurements will get.

The best we might be able to hopeful is for same model meters to give similar results on the colored LED's, and hopefully some consistency with the white LED and the incan across brands/models. Even meters with current certifications will probably vary when measuring source that are outside of the calibrated spectrum.

SilverFox and McGizmo posted a lot of details about this back on 10/7-8. If I've said anything different from them, believe what they posted, not mine!


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## bwaites (Oct 20, 2005)

There is no doubt that the meters, and their filter systems, will have a huge influence on the findings. 

But look at LEDMuseum and my results with the same meters, though mine is much newer from what Tom told me, they are both LM631's.

Has Meterman significantly changed the filter system?

And why so much variation on the A2, actually more than the variation on the white LED?

Oh well, guess that is why we test!

Bill


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## HarryN (Oct 20, 2005)

It is pretty common in the metrology world to find callibration variations of 20% instrument to instrument, even within the same brand, and regular maintenance. If we stay within 2 x this, I will be impressed.

I guess this info might indicate that Bill's power incans are even brighter than he has been saying ?


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## SilverFox (Oct 20, 2005)

Hello Ray,

I have added you to the list.

Tom


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## Codeman (Oct 20, 2005)

:thanks:


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## Bogus1 (Oct 20, 2005)

Hi Tom,

I don't use primaries, but I have some new ones sitting around. However I tested these and I have 1 SF that tests at 3.16v and 2 Sanyos that test at 3.11v. I have more that test at 3.10v and 3.09v. Are these adequate or should I order new batteries? I'll order them right away, but I don't want to create any hold up.

Thanks


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## SilverFox (Oct 20, 2005)

Hello Bogus1,

My gut feeling is that you should be OK with what you have. 

Craig and I did the testing with two batteries. We started with both batteries in the A2, then took one battery and tested two colors, then the other battery for the other two colors.

I did not check the voltage of those cells at the end of the test, but there was no indication of any reduced output. I believe all the drivers are well regulated even at lower voltages.

You may want to send Craig (The LED Museum) a PM and see if he can check the voltage of the batteries we used for the test.

Tom


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## The_LED_Museum (Oct 20, 2005)

One cell measures 3.059 volts, and the other measures 3.060 volts, using the 4VDC scale on my DMM.

Using the battery tester I purchased from Emilion's Workbench (which tests the cells under a 120mA load), I received readings of 3.07 volts and 3.07 volts.


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## SilverFox (Oct 20, 2005)

Thanks Craig,

Bogus, it looks like you should be good to go with what you have.

Tom


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## bwaites (Oct 22, 2005)

Priority Mailed to Sigman today, insured for $500.

SilverFox, reflectors in the mail as we discussed. Priority also.

Bill


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## wptski (Oct 22, 2005)

Just looking at the results by meter type and was amazed by the difference in the two LM631! The A2 and white are close but the rest are a mile off!! Something had to change in the LM631 along the line somewhere. I wondering how my LM631 will test?


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## SilverFox (Oct 22, 2005)

Hello Bill and Bill,

Bwaites: Thanks, I'll let you know when the reflectors get here.

Wptski: I wonder if there is a date code in the serial number on those meters. I am not sure we can figure out if certain meters came from the same batch or different ones.

Tom


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## Kiessling (Oct 22, 2005)

As long as white LED and incan are rather accurate I am a happy camper ... 
bernie


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## wptski (Oct 22, 2005)

SilverFox said:


> Hello Bill and Bill,
> 
> Bwaites: Thanks, I'll let you know when the reflectors get here.
> 
> ...


Tom:

Yep, there is a number! It's 0401299. Wonder if that could be #299 in Jan. 2004, April of 2001 or something else? Don't remember when I got it but I've had for some time.

EDIT: Can't be in 2004 as thats when I joined!


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## Sigman (Oct 25, 2005)

Status check...

Received the lights, hope to get the tests done tonight and mailed to Bogus1 Wednesday.

Bogus - I'll PM you for your address.


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## Sigman (Oct 26, 2005)

Ok...first of all, haven't heard from Bogus1 for his address.

Well, we paced off 10 strides from the barn and then averaged out the strides to be approximately 3 3/4 of my size 12 shoe which gave us the 39" we were looking for to set up the lights that were duct taped to back end of our mule (who just wouldn't stand still unless we were feeding him sugar cubes , geesh - we had to run to the store and find the brand that ole' Charlie liked as he will only eat a certain brand - the ones in the pink and white box - but that's another whole story for another time!)

So after we scratched our setup lines in the sand with a stick, we got some more duct tape (oh BTW - Charlie sure didn't like that duct tape being pulled off his rump - bout' got the "stuff" kicked out of me doing that one!)...and taped the specific light that we were testing to a ladder (which was a whole lot steadier than that mule's backside!) and aimed it at the mark we painted on the barn. Wouldn't you know it, there was a hole right where we planned on nailing the meter up! So we got a little board and fixed the hole, then we had to readjust the ladder as it was off about a half of a heel (as compared to my boot). 

Next we fished around in the tackle boxes trying to find those spare 123 batteries that we took fishing last week...I don't think the worm slime will affect the voltage - we rubbed it off real good with my shirt.

So we loaded the batteries in the lights - but noticed that the duct tape was just so slightly covering the sensor on the LM631 - but that worm slime really takes the sticky stuff off real good, glad I still had some that hadn't dried out on my shirt!

About that time JOshooter started up the tractor cause it was gettin' kind of chilly outside and we thought the exhaust would warm us up a little - well you know that wasn't a good thing to do...so...

Ok reality sets in:

Keep in mind the posts of Silverfox, McGizmo, NewBie, and perhaps other posts I've missed above in reference to calibration of light meters to Standard Illuminate A and the spectral response/sensitivity of light meters. 

My results:

Battery: Titanium (from Amondo Tech) - each cell measured 3.31 VDC
Room Temperature: 70.2 deg.
Meter: Meterman LM631 s.n. 0205072 (readings in LUX)
Distance from front bezel to light meter sensor 39"/1m
Meter mounted against blank white wall w/no reflective surfaces in the perimeter.

*A2 *- 2310, 2400, 2360 for an *Avg: 2356*
_White LED_ - 1080, 970, 1020 for an _Avg: 1023_
Blue LED - 270, 260, 248 for an Avg: 259
Green LED - 2410, 2370, 2240 for an Avg: 2340
Red LED - 800, 780, 810 for an Avg: 796

Consistancy in setup is so important...We had some readings that "baffled us" (for lack of better words) - but we took them over again and this set seems to be the most consistent.

Have I left out anything? Yes, I would like to thank JOshooter for his assistance in conducting this test. We aren't rocket scientists (well ok, I'm a radar/communications/navigations/weapons systems/flight controls/avionics/computer/electronic technician/inspector by trade & JOshooter is studying to be a Civil Engineer), but I don't think we messed it up too bad. Heck, I looked for some white lab coats that we could wear, but couldn't find any - so we took bed sheets and wrapped them around us "Toga Party" style instead, oh and had the "Blue's Brothers" sunglasses on for protection from all those photons & UV thingys that were escaping from those lights...woooohooooo!!!!

Soon as I hear from Bogus1 - I'll get the lights sent to him or someone else if I don't hear from him in how long????


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## SilverFox (Oct 26, 2005)

Hello Sigman,

It is nice to know that in the "Land of the Midnight Sun" you were able to find enough darkness to conduct the tests...  

I am sure that any deviations in your results will be attributed to worm slime...

I have added your results to the first post.

Bogus1 is next on the list. If he does not reply, get in touch with the next person on the list and we will just move Bogus1 down one notch on the list.

Tom


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## Sigman (Oct 26, 2005)

Bogus1...CPF Calibration Lights on the way to you via USPS Priority, insured w/delivery confirmation.


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## wptski (Oct 27, 2005)

Sigman said:


> Bogus1...CPF Calibration Lights on the way to you via USPS Priority, insured w/delivery confirmation.


"With Delivery Confirmation"? You have to be home and sign? If a adult isn't home to sign, they leave a slip or you can pick it up but this could add 1-2 days to the mix. I once had a package that took five days for me to get and I think that the postal carrier got in deep poopoo over it!!


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## Sigman (Oct 27, 2005)

wptski said:


> "With Delivery Confirmation"? You have to be home and sign? If a adult isn't home to sign, they leave a slip or you can pick it up but this could add 1-2 days to the mix. I once had a package that took five days for me to get and I think that the postal carrier got in deep poopoo over it!!


According to this in the 1st post:



> 8 - You will need to pay the postage and insurance required (the insurance value of these lights is $500, and we can call them benchmarking lamps) to send it to the next person and make sure it gets packaged securely and sent out.


...delivery confirmation not required - personal choice by myself.


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## Sigman (Nov 1, 2005)

...background radio static/noise, "Sigman to Bogus1, over?"

Receipt confirmed...thank you sir!


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## Bogus1 (Nov 2, 2005)

PM sent to evan9162 for your address. The lights are ready to ship to the next in line.

It took me well over an hour to do the tests.

The temperature is 68 degrees and I have a fixed light meter set up with a tripod for standardized testing using a Meterman LM631 purchased in a group buy some months ago. The edge of the tripod lip I use for reference at 39 3/8". The meter is located several feet from any back drop in a room with 14' ceilings. 

I have always thought my white LED readings were low and this seems validated. However I would like to mention I was very frustrated checking the lux on the white A1. There is something wrong with this head IMO. I've owned many Alephs, and none of them had the artifacts in the beam this one has. It appears the LED isn't centered with the reflector. The head doesn't appear to be damaged and the LE appears fixed. I am kind of picky though, so maybe this is nothing.

----------------------------------- Average
SF A2: 2420,2400,2400---------------2407
A1 white: 887, 854, 850---------------864
A1 blue: 854, 850, 852----------------852
A1 green: 1342, 1359, 1352-----------1351
A1 red: 2470, 2420, 2420-------------2437

I used 2 Sanyos in the A2 that began at 3.11 volts each and ended at 2.92 volts. The Aleph white A1 began at 3.16 volts and ended at 2.92 volts because I repeated the test with little variation. I used the 2 Sanyos on the remaining LEDs.

I increased the sensitivity on the meter when readings were below 2,000 lux for greater accuracy.

I would suggest logging readings without checking the results from previous posters, at least for the first round of results before attempting to understand the variations. Some of my results are completely out of whack with the norm. It appears my unit has a bias and that needs to be shown as does the variation in the testing itself.


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## SilverFox (Nov 2, 2005)

Hello Bogus1,

I have added your results to the first post. Thank you for your help in collecting this data.

Evan, it looks like you are next on the list...

It is simply amazing how consistent our meters are turning out to be... :nana:

Once again, let me state that there is no "right" number. The purpose of this testing is to see where we are in relation to what we are using to measure our lights. 

On second thought, there eventually will be a "right" number, but that will have to come from a certified laboratory. 

Until then, I am simply realizing that when lux values are given, there is the distinct possibility that the + or - tolerance may be quite significant, even on the same light...

Tom


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## evan9162 (Nov 2, 2005)

Yup, I PMed my addy to Bogus this morning.


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## McGizmo (Nov 2, 2005)

Bogus1,

I can't remember where the thread is on these lights themselves but I am suspicious that the "issue" you have with the A1 and its artifacts is based on a rather smooth reflector coupled with our friend, the "Joker".  :shrug: I think I recall considering this issue which came to light for me about the same time but given the fact that the reflector and LE are epoxied in on this particular A1, I think I recall saying something about F it.


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## Bogus1 (Nov 2, 2005)

I sent the lights off just after noon today so hopefully Evan will have these Friday. Thanks everyone for the opportunity to participate and I look forward to understanding from all this!


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## bwaites (Nov 2, 2005)

Bogus,

Actually, your readings and my readings aren't too far out of whack.

Bill


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## NewBie (Nov 3, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



SilverFox said:


> Hello Bogus1,
> 
> I have added your results to the first post. Thank you for your help in collecting this data.
> 
> ...




For the same white source, it looks to me that the meters are very consistent.

Where I see alot of variation is in the colored sources.

To me, this would indicate, that depending on the color bin of an LED, where it lies in a color bin, and what the actual spectrums are of a group of leds are (and they do vary quite a bit, even with parts that look identically white), a wide variation in readings, from various white LEDs from meter to meter would be expected.

This makes alot of sense, due to the different photodiodes in the light meters, and the integrated/external color filters that were chosen for each light meter, and the consistency of the sensor/photodiode combos by brand/model.

It would be additionally interesting to group your results by brand/model of light meter.

It would be very interesting to send a group of white LED lights from various bins, through the same group of folks.


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## evan9162 (Nov 5, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Got the package notice today, will try to pick up tomorrow. If I can't, it'll be monday.


----------



## SilverFox (Nov 5, 2005)

Hello Newbie,

An interesting question comes to my mind...

White LED's have a strong blue component (spike) in their spectrum.

If there is so much scatter in measuring a blue LED, how can the white LED measurement be so consistent?

Tom


----------



## NewBie (Nov 5, 2005)

*Re: Light Meter Benchmark Testing – CPF style*



SilverFox said:


> Hello Newbie,
> 
> An interesting question comes to my mind...
> 
> ...




There is very little "lumen" power in the blue. To make white, it takes very little blue light. In an RGB setup, the lion's share is in the Green, then the Red, and then the blue, where the red is only like 1/3rd of the power of the green, and where the blue component is only 1/2 of the red, so like 1/6th of the power is in the blue. This will vary, depending on the wavelength of the blue, and the actual efficiency of the LEDs. 

I've seen the blue component on LumiLEDs parts anywhere from 430 to 480 nm. FYI, depending on the exact YAG phosphor used, the peak wavelength conversion efficiency occurs around 465nm. This variation in the blue die under the phosphor, contributes greatly to the variation of the binning on the LumiLEDs parts. Of course, the phosphor thickness and such also contributes...


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## evan9162 (Nov 5, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Can't pick up packages today - so it'll be monday before I get this.


----------



## evan9162 (Nov 7, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Got them today. Should have some results later tonight.

Unless there are objections, I'd like to change the packaging just slightly - hopefully this will be reusable by everyone else in the passaround. I found some 2" high density foam at work that was in some shipping boxes that were in the toss pile - this foam was used to ship networking equipment, so it should also be static safe.







I made a cutout block for the two lights and 3 alternate heads - It'll be covered up by another layer of foam on top. I'll also include the packing materials I received, and store them underneath everything. This should provide a nice secure shipping medium, not much larger than the box I received, and will be handy for those doing the tests as there will be a place to put the lights/heads to keep them safe when they're not in use.

What does everyone think?


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## SilverFox (Nov 7, 2005)

Hello Evan,

I think the packing looks good. My only concern would that it would cost a bit more to ship and I don't want to impose a hardship on anyone.

Are you planning to do some lumen measurements too? I would be very interested in what you come up with...

Tom


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## evan9162 (Nov 7, 2005)

Yeah, I think the foam only adds a couple oz total. I'll go ahead and ship it this way, and let everyone know what the cost was. If it's substantially more, the next person in line can go back to the other packaging (I'll include it in the box) - The foam was free, and took about 10 minutes to cut up, so no biggie if it doesn't work out. 

So if it doesn't work out, the original packaging can be used, and I'll be the only one out on any extra shipping charges.


[edit]
Yeah, I'll be doing the lumen integration to see how it fares. I'm really interested to see if the measurements that I've taken that seem low are an artifact of the technique, or my meter its self.


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## evan9162 (Nov 8, 2005)

[edit]

Duh -forgot some important info

Meterman LM631 light meter. Ambient temp was 16C (61F)
I bought my LM631 from CircuitSpecialists.com almost exactly 1 year ago.


Okay, got my testing done, here are my results:

```
Light	Lux	Calc Lumens
White	868	33
Blue	919	36
Green	1340	25
Red	2420	54
A2	2265	52
```

My lumens calculation is based on using my angle measurement rig to vary the angle of the light to the light meter, so I can generate an intensity profile. I then use some geometry and the definition of Lux (1 lux = 1 lumen / sq meter) to integrate the measurements together. Note that the lumens calculation is dependent on a few assumptions:

1) The light meter reads correctly
2) The light output is quite uniform in shape - the sensor dome is about 1/2" in diameter, and serves to average the intensity over that area well, but if the beam is not completely symmetrical or uniform, that can introduce errors
3) The angles I'm rotating the device through are exact

Right now, I can tell you that all 3 assumptions are wrong for this particular setup (measuring lights with an optical system). 

1) My light meter is reading quite differently than others, I have no doubt now that it's reading low for white and green lights

2) Optics and reflectors introduce beam artifacts, which can be hard to integrate unless the light is tested many times by physically rotating the light in the test rig, in an attempt to integrate all the beam artifacts and get a better average. *However*, measuring bare light sources is much more accurate, as bare LEDs without optics (Luxeons, Cree XL series, etc) produce very uniform and smooth beams

3) My test rig isn't exactly built to NIST standards. While I have 1-degree measurements, there is some slop/play in the rig, and claiming 1-degree accuracy is spotty at best. Again, for measuring bare LEDs, this is fine, and I don't need much more than a couple degrees of accuracy.

I don't think my test rig is accurate enough to measure beam angles and integrate to lumens for lights with reflectors or optics. But, I think it is accurate enough to produce good integration numbers for bare LEDs.

Here are the beam profiles of the lights - the full profile, and zoomed to the 10-60 degree range:












Just for fun, here are my measurements, with some correction factors based on the numbers from everyone else's tests - I eyeballed what the "real" value for the lux measurement should be, and used that to produce a correction factor to apply to the lumens number. The corrected value is much closer to the real value:


```
Light	Lux	Calc Lumens	"real" lux	factor	corrected lumens
White	868	33		1200		1.38	46
Blue	919	36		350		0.38	14
Green	1340	25		2800		2.09	53
Red	2420	54		2400		0.99	53
A2	2265	52		2450		1.08	57
```


Here are photos my my measurement rig:






In the foreground is the light holder that can turn, and in the back is the light meter.


The light holder allows the light to be rotated both ways. The first 10 degrees in either direction has 1-degree graduations. The axis of rotation is set up so that it rotates around the light source, so there is no change in distance to the meter throughout the rotation - giving true measurements of the beam profile.







The light meter sensor is underneath a heavy black sheet, behind the cardboard baffle. The hole in the baffle is about 1" in diameter. The backside of the baffle is covered in black construction paper. The sheet is draped over the sensor, and tucked in so no light will leak in. The only way light can get in is through the hole in the baffle, and then only on-axis light hits the sensor. With the light meter set to the 10 lux scale, and the lights on in my garage, I read only 0.05 lux of background light. So my measurements shouldn't be affected by either ambient light, or any reflections.






The sensor is held in place with a T-shaped board arrangement. The LM631 sensor has 2 banana plugs on it, so drilling two holes in a surface will allow you to plug it into place. The light sensor is setup so that it is at the same height as the light being tested. In the setup, I attempt to do my best to make sure the light and sensor are coaxial and colinear.







I could definitely stand to improve the test rig by tightening up the tolerances of the rotation shaft, and producing a more accurate angle scale. Plus, having a 1/2 degree verneir would allow for better measurement. 1 degree at 1m is about 5cm - to be really accurate, you'd need to move the rig so that an area no larger than the sensor dome is measured at a time - since that's ~1.3cm, I'd need to be able to vary the angle accurately by 1/4 degree. Eek!


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## SilverFox (Nov 8, 2005)

Hello Evan,

Interesting...

I need the make and model of your light meter and a rough guess as to the temperature during the tests.

I look forward to seeing your pictures.

Tom


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## evan9162 (Nov 8, 2005)

Silverfox,

Sorry bout that - updated the info at the beginning of my post. (LM631, temp 61F)

I noticed that there's a lot of variation with the LM631 meters. Perhaps we should all post the serial number (if there is one) of our meters to see if there's some commonality of those with similar measurements (lot numbers, mfg date, etc).

I also noticed that for the LM631s, the white luxeon measuring low and the green luxeon measuring low go together. The low green measurement probably causes the low white measurement, since green light is an large component of the white LED spectrum.

[edit - figured out how to upload from work]

here are the LM631 meters graphed:






It looks like there are two distinct varieties of LM631 with different spectral responses (this graph excludes the A2 measurements)


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## SilverFox (Nov 9, 2005)

Hello Evan,

Nice set up.

The data does seem to suggest that there are two different Meterman meters, or at least there is a change in the photo diode or correction filter.

I have added your data to the first post. 

So far we have 10 data points with 6 of them from the Meterman. I guess we can start speculating trends. It is an interesting observation about the correlation of the response from the green LED and the white LED.

I am eagerly awaiting the results from the others. I believe once we have 30 or so readings, we will be in a better position to speculate. 

Any other comments...?

Tom


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## The_LED_Museum (Nov 9, 2005)

The serial number of the Meterman LM631 I used is *0205161*; no date of manufacture is shown.


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## wquiles (Nov 9, 2005)

evan9162,

That is a freaking cool setup you have there !!!

Will


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## evan9162 (Nov 9, 2005)

The_LED_Museum said:


> The serial number of the Meterman LM631 I used is *0205161*; no date of manufacture is shown.



Thanks Craig,

Mine is 0405053. I bought mine at the end of 2004 - did you happen to get yours in 2002? I'm wondering if the manufacture date is somehow encoded in the serial number...


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## evan9162 (Nov 9, 2005)

I PM'ed Chevrofreak yesterday morning and haven't gotten a response. It looks like he might not have been online for about a week now - perhaps I should move to the next person?


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## HarryN (Nov 9, 2005)

That is some very nice work Evan. I have attempted somewhat more simplistic beam scans by having the light fixed, and making a "flat distance" scan 1 meter away. The point in that case was not to measure Lumens so much, but to see how well things are lit up at a particular distance (sort of a flat wall test).

The profiles were more or less similar, but your setup is more precise.

I am in line with your thinking that there are two very different meter setups. Even with only 3 data points each, there is enough information to see that the plots are bimodal. It will be nice to see how the data plots out as more info is collected. I haven't had this much data for decision making in years.

Last but not least - which data set is better at aligning with the IS data ?

Edit - I went back and looked again at the plots from Don's IS for the white. It occured to me that the peak for blue is quite narrow, and the output dip for in the green area is quite wide (for a white LED). The data could also be explained by a relatively small shift in the wavelength sensitivity. - as in 10nm. Now I really am confused.


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## evan9162 (Nov 9, 2005)

Harry,

For the values I eyeballed for the lumens correction factor, I used the values for meters #1,#2, and #4 (the upside-down V shape) - with the correction factor applied to my "lumens" value, the corrected lumens figure comes pretty close to Don's IS measurements. 

My meter response graph was only for LM631 meters. It would also be interesting to plot some of the other meters as well - I was seeing if there was some order to the apparent chaos of the LM631 readings.

Meters 1,2,4 look like they have a response very close to human eye response. Strangely, meters 3,5,6 look like they have a response close to the emission pattern of an incandescent light source. Wierd.


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## evan9162 (Nov 10, 2005)

Silverfox,

It's been 2 days, and I haven't heard from Chevrofreak - I'm going to move on and send the lights to the next on the list (andrewwynn).

Sound good?


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## SilverFox (Nov 10, 2005)

Hello Evan,

Sounds good to me. We can always catch up with Chevrofreak at a later time.

Tom


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## wptski (Nov 10, 2005)

Tom:

Is it possible for you to add the serial number/date code of the meters used to your meter list? Maybe previous and future testers could provide this info. I'd like to see that info for the LM631 which appear to show a trend!


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## McGizmo (Nov 10, 2005)

My LM631 is serial # 0309156 and it has CIE illuminant standard A (approx. 420 - 720 nm)

Nice set up Evan9162 ! :thumbsup:


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## rdshores (Nov 10, 2005)

I called Meterrman and asked about the serial number and the date of manufacture. For a number like 0504531, the 05 is the year, the 04 is the month, and the 531 is the sequence number.


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## chevrofreak (Nov 10, 2005)

Sorry about that, I've been away from CPF for a while.


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## Bogus1 (Nov 10, 2005)

My LM631 Serial # is 0503031


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## evan9162 (Nov 10, 2005)

Thanks McGizmo,

Question for the masses (I seem to be very chatty in this thread) - When I was doing the beam angle measurements for the A2, it seemed to "click" into a low-power mode after being on for 5-10 minutes. The light was rather warm when this happened, and turning it off for a few minutes let me run it again for a while. 

Does the A2 have some form of thermal protection where the regulator puts the light into a low power mode if it's getting too hot?


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## SilverFox (Nov 10, 2005)

Hello Evan,

I see Chevrofreak is back with us...

I seem to remember Don showing the A2 running in regulation for something close to 50 minutes. I believe it will not shut down due to thermal issues, but will shut down on low voltage.

I will update the data to reflect the Meterman serial numbers. I don't have Bill's serial number, but we may have to wait until he gets back to get it.

Tom


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## evan9162 (Nov 10, 2005)

Hmm - interesting - perhaps it was the batteries - I was using Battery Station CR123As. Maybe they have some kind of thermal protection or something...

I'll be mailing the lights to Chevrofreak tomorrow morning.


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## evan9162 (Nov 11, 2005)

I just mailed the package to Chevrofreak

With the new packaging (cut-out foam) and the old bubble wrap added in the box, the shipping for UPS ground with $500 insurance was $10.80 - I saw an ~$11 figure for using USPS with the smaller packaging - it appears that UPS is slightly less in this case because of the insurance.


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## SilverFox (Nov 14, 2005)

Hello Evan,

I was just looking over your data and a few questions came up...

First, would it be possible for you to do a graph of your beam profile utilizing a log scale for lux? I think there may be some very useful information there, but it is difficult to see on a linear scale.

I noticed that there is quite a difference between your lumen numbers and Don's. We all know that Don's set up is not fully calibrated yet, but I still was thinking that the measurements would be closer.

You mentioned that the reflector introduced artifacts into the beam and you could do better with bare LED's. I am under the impression that all LED's have an optic on them. It seems to me that introducing a reflector to gather the spill light from the LED's optic and project more light forward should result in higher lux values that could influence your lumen calculations.

Yet, when I review your lumen values with Don's, I see that in the broad spectrum measurements (White LED and A2), you are only getting about 65% of what Don reported. I chose the broad spectrum lights because that is what our light meters are supposed to be calibrated to. I think our meters should be pretty consistent measuring the A2, because that is what most meters are calibrated to.

How does focusing the beam result in a calculated 35% loss in lumens?

I have been trying to get my mind wrapped around this for a while, and seem to be slipping into oblivion. Any thoughts you have would be apreciated...

Tom


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## HarryN (Nov 14, 2005)

Hi Tom

At least when I did "X Scan" measurements of bare vs focused beams, the challenge I had was that the meter has a much larger capture area than the visible variations in the beam.

A good worst case example is a cheap 2 D light. The beam is full of artifacts, bright spots, nearly dead zones, etc, even in the hot spot, but the meter does not have the resolution to really represent it. It also does not really do well crossing from the hot spot into the corona. Surpisingly, even with a mask on the meter, it is hard to find these things.

The bare LEDs, at least the Lux IIIs I tested, had such nearly-perfect uniform output over a broad area that the measurent accuracy is relatively easier to deal with.


----------



## evan9162 (Nov 14, 2005)

Harry pretty much covered where the variations come from, but here goes



> First, would it be possible for you to do a graph of your beam profile utilizing a log scale for lux? I think there may be some very useful information there, but it is difficult to see on a linear scale.



Sure, I can do that.



> You mentioned that the reflector introduced artifacts into the beam and you could do better with bare LED's. I am under the impression that all LED's have an optic on them. It seems to me that introducing a reflector to gather the spill light from the LED's optic and project more light forward should result in higher lux values that could influence your lumen calculations.



A bare luxeon without a reflecor or focusing optic will yield a beam pattern that's quite wide and smooth, where the falloff is very gradual and the beam is almost perfectly uniform without artifacts. That lends itself well to the assumption that the point I measure with the light meter at a specific angle will have the exact same brightness measurement as any other point in the beam at that angle from 0 degrees. This assumption falls apart when the beam isn't perfectly uniform - reflectors and optics tend to cause the beam to have imperfections and sharp falloffs (like the transistion from the hotspot to the spill light). These aren't accounted for properly by measuring one spot in the beam and assuming that that measurement is representative for all points at that angle.




> Yet, when I review your lumen values with Don's, I see that in the broad spectrum measurements (White LED and A2), you are only getting about 65% of what Don reported. I chose the broad spectrum lights because that is what our light meters are supposed to be calibrated to. I think our meters should be pretty consistent measuring the A2, because that is what most meters are calibrated to.



I think that most of the difference in the white LED lumen calculation is accounted for in the difference between what his any my meters measured - mine was in the high 800s, while his in the high 1100s. I'm pretty convinced that my meter measures 20-30% low for white LEDs. It only seems to be off by maybe 5-10% for incandescent lights.

As for the A2 - the A2 has a slightly oblong beam shape - if I had measured the short diameter of the oblong (which I likely did), I could be missing a lot of the "lumens" by assuming the short diameter was representative of the whole beam, making the beam seem narrower than it really is - losing some lumens that weren't accounted for in the wider part of the beam.

The main reason for my inaccuracy with the focused lights is that 50-60% of the light output is in the first 10 degrees off-axis - to accurately measure those with my setup would require the ability to accurately measure and rotate to 1/4 degree increments. I noticed there was something like 1 degree or more of slop in the axis of rotation. 

So basically, the reflectors put a huge chunk of the output into a tight region which I can't really measure accurately. They also introduce artifacts that I'm unable to account for - either by introducing blotchiness or an uneven beam shape. I'm not too surprised that some of the measurements are off by as much as they are.


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## SilverFox (Nov 14, 2005)

Hello Harry,

OK, help me through this...

I was under the impression that an integration sphere "averages" the beam so an accurate measurement can be made, in spite of the various artifacts present in it.

The light meter also has an integrating dome on it that should also average out the artifacts in the beam.

To me, this suggests that as you move off axis, your "average" reading would be on the high side, thus your lumen measurement would also be on the high side.

I am sure I am missing something... Where am I going wrong?

Tom


----------



## SilverFox (Nov 14, 2005)

Hello Evan,

You posted while I was responding to Harry.

I am beginning to understand the problem.

Another question... If you took measurements at a greater distance, would that tend to smooth things out to a point where more accurate measurements could be taken?

Tom


----------



## evan9162 (Nov 15, 2005)

Tom,

It would tend to even out beam artifacts more, and would help accuracy that way. But the problem with measuring out farther is that as you get farther away, each degree of rotation covers a larger area. The formula for length of arc is l=r*theta, where theta is the angle in radians.

It would be most accurate for each measurement (in the first 10 degrees or so of the beam with reflectors) to be made such that the angle of rotation results in the beam where it strikes the light meter doesn't move more than the diameter of the sensor dome. The LM631's dome is something like 1/2" in diameter. 

At 1 meter, 1/2" (0.0127 meters) results in an angle of theta=l/r, or 0.0127/1, or 0.0127 radians, or 0.7 degrees (okay, I was wrong above, I somehow before calculated that 1/4 degree was needed)

At 2 meters, 1/2" (0.0127 meters) results in an angle of 0.36 degrees.

So increasing the distance also means increasing the accuracy by the same amount.

I suppose that means that I could always measure at 1 foot with footcandles, then convert to lux (1 Fc at 1 ft = 10.76 lux at 1 m). At 1 foot (0.3048 m), the diameter of the sensor dome means I only need 2.4 degree accuracy. That's easily managable. The problem is that when you're so close, the beam gets small, so you lose the ability to accurately differentiate different parts of the beam, and the profile is now inaccurate - more of the beam is concentrated on the sensor at one time.

What I really need is the head from a telescope mount - they have nice slop-free (for the most part) axis', graduated dials with 1 degree (or better) accuracy, and slow-motion controls to make angle changes easier - that would definitely improve the accuracy, and probably let me measure at 2 meters.

[edit]
Here's the log version of the beam angle graph:


----------



## SilverFox (Nov 15, 2005)

Hello Evan,

It looks like there is a bit of a catch 22 going on. Close up you encounter beam problems, and further out you lack degree precision...

Thank you for your explanation. I am beginning to see why they take measurements off of an integration sphere. It seems to eliminate some of the issues with geometric measurements.

I find the log graph very interesting. It seems that the LED lights and the incandescent have similar hot spot shapes, but the incandescent has a wider spill. It is also interesting to note the difference in brightness between the hot spot and the spill. I was expecting less than 2 orders of magnitude difference in the incandescent. I am not sure why, but it seemed that the spill of the A2 was brighter than that.

Oh well. Enough questions for now. Thanks for helping me understand this.

Tom


----------



## evan9162 (Nov 15, 2005)

Yes, indeed. For an evenly illuminating light source (like a bare luxeon, or other power LEDs that don't focus) the geometric method is actually quite good, and is probably pretty darn accurate, even given the inaccuracies in my equipment - the only critical part is a light meter that reads accurately.


----------



## SilverFox (Nov 15, 2005)

Hello Evan,

Ah yes... wouldn't it be nice to have an accurate light meter... 

This benchmark testing is a real eye opener for me.

Tom


----------



## HarryN (Nov 15, 2005)

My "test rig" is a bit more crude than Evan's, but also had a slightly different purpose. In his case, he is very interested in the LED itself and total Lumens. In my case, I am trying to find a simple method to graphically represent a "1 meter white wall test".

I was, and continue, to look for a good method to compare beams from various optical combinations. This is a big deal when trying to develop 12mm optical systems.

The test setup, is a 2 in x 2 in x 10 ft long board suspended on two ladders. The board is approx 1.1 meters from the ground, and is marked off over a 2 meter distance every 1 cm.

I set the test light so it is 1 meter from the board, facing up, with the hot spot centered on the board. The meter is then X scanned every 1 cm across the beam, giving a reasonable indication of the wall reflection concept.

It has a few bugs that I am still working on:

1) The dome of the meter integrates a rather large area, so it tends to smooth out the actual measurements.

2) When you are 1 meter from the center of the hotspot, the meter reading can (sometimes) be sensitive to the angle (held facing straight down vs at the light source). Normally, this is not an issue, until # 3.

3) In an attempt to improve resolution, I put the meter in a small box with black construction paper surrounding it, and a 10mm slit. The idea was to reduce the acceptance area. Nice theory, but in practice, it did not appreciably help. (Maybe the slit is still too large). Also, the acceptance angle issue really starts to show up at the edge, and there can be a dramatic change in Lux readings depending on whether the meter is facing "down" or "toward the light source". I am not sure which is more correct. 

4) I thought the rig was pretty good, but it is surprising just how sensitive the readings can be to very small elevation and hot spot location changes. 

5) The scan is only in one dimension, and a surprising number of beams are not round. 

6) The test is very time consuming, and you have to stand over the beam of the light and take readings - so there is a very real limit to how bright of light is practical. I find 1,000 Lux to be ok, 2,000 is a real push.

I have seen an automated version of this setup, which can collect even more data points, and it used a VERY narrow sensor opening.

Suggestions of course are welcome.


----------



## chevrofreak (Nov 16, 2005)

I got the lights yesterday and fiddled with them last night. Some of my readings were nearly exactly what's been posted and some were way off the mark. I'll test again tonight and then post my results.


----------



## SilverFox (Nov 16, 2005)

Update:

Archangle is having some scheduling conflicts and has asked to be moved further down in the schedule. I put him in after Cy. I believe that should give him time to get things settled.

Tom


----------



## SilverFox (Nov 16, 2005)

Hello Chevrofreak,

Glad to hear that you received the lights...

Keep in mind that we don't know exactly what the mark is... at least not yet. We won't know until we have a laboratory test the lights.

Just report what you get and I will add it to the results. If it seems a bit off, it will give us something to speculate and ponder about... 

Tom


----------



## chevrofreak (Nov 17, 2005)

Here are the results that I got the other night, and they are puzzling. I have my sensor about 8" off of a table which is covered with a blue terry cloth towel to cut down on reflection. There is a line marked at 39" and i set the lights ontop of a box the same height as the meter when I take measurements. You'll see whats puzzling about my readings....

Aleph 2
White : 1176 then I tested the other colors and came back for a second test with the white, which came out 1420 :thinking: 

Red: 1080

Blue: 2078

Green: 2805

A2 Aviator: 2780 then 2765

I'm going to test again tonight with a fresh set of batteries and post those results, then mail the lights on to Andrewwynn tomorrow.


----------



## chevrofreak (Nov 17, 2005)

Another odd thing is that the battery in my meter seems to make a difference. 

With a Rayovac Maximum Plus 9v in it the meter reads -000 when the sensor is completely covered. With a Rayovac Heavy Duty it reads just 000. With the Heavy Duty in and only the light furthest from the meter turned on and me standing between the light and the meter it will read about 003-005 but with the Maximum Plus it reads dead 000 even though there is a small amount of ambient light. It really makes no sense to me. I think I might have someone build me a 9v regulated power supply that I can drive off a larger battery and see what that does.

When it gets dark later I'll repeat all of the measurements and post the results.

Heres a pic of the guts of the sensor in my Watt Stopper FX-200


----------



## Pinter (Nov 17, 2005)

HarryN said:


> My "test rig" is a bit more crude than Evan's, but also had a slightly different purpose. In his case, he is very interested in the LED itself and total Lumens. In my case, I am trying to find a simple method to graphically represent a "1 meter white wall test".
> 
> I was, and continue, to look for a good method to compare beams from various optical combinations. This is a big deal when trying to develop 12mm optical systems.
> 
> Suggestions of course are welcome.


HarryN,

I just started a project on comparing relative brightness and beam distribution of different leds and optics. I do not need the absolute numbers, just want to know the beam characteristic _relative_ to each other.

I am using a simple 3MP digital camera. I am taking pictures with fixed settings from let's say 1 meters. Then I convert the pictures to 256 grey level tiff images. This is the input of my software.
All you need is to know the horizontal field of view (H-FOV) of your camera. You can easily calculate it by taking a reference photo from the given disance on a tape measure and read the viewable length. 

The software automatically finds the possible center of the beamshot (or you can also set it manually) and generates text file output with the brightness levels at custom degree steps. E.g. you can easily generate the beam characteristic on +/- 20 degrees with 0.1 degrees resolution in some seconds.
This file then can be read by Excel.

So once you have the black and white tiff files of the different leds it takes only some minutes to generate text files, import to Excel and make nice comparative graphs on them.

Now the software can only generate beam characteristic on the horizontal direction, but the next feature will be a rotatable axis. E.g. beam characteristic axis rotates around the beam center from 0-350 degrees in 10 degrees steps.


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## HarryN (Nov 17, 2005)

Pinter - that is a very interesting method. I am planning a Christmas digital camera purchase, and your idea would be a much easier and more accurate method than my current approach. I might be back asking about more advice on the implementation once the camera is purchased.

Thanks - Harry Niedecken


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## chevrofreak (Nov 18, 2005)

Final results

Aleph 2

White: 1420 1445
Red: 1080 1070
Blue: 2078 2070
Green: 2805 2770

Surefire A2 Aviator: 2780 2730 2765

I held the light infront of the meter and hunted for the highest reading from 39"

meter: Watt Stopper FX-200


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## SilverFox (Nov 18, 2005)

Hello Chevrofreak,

I also need the room temperature you had during your observations.

I have added your results on the first post. It is interesting that your meter had a very healthy blue response.

I should point out that the graph shows the data in the order it was tested. The spreadsheet is trying to show the Meterman meters grouped together.

A point of clairifacation...

I believe all of the LED lights are Aleph 1. At first Don was going to build a White Aleph 2, but when we went with 4 different colored LED's, that changed to Aleph 1 lights.

Andrew, you are next...

Tom


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## andrewwynn (Nov 18, 2005)

can't wait to get it.. chevro already PMd me for address.

-awr


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## chevrofreak (Nov 18, 2005)

Yeah that was my bad, the whole A2(aviator) A1 thing got me cornfuzed :thinking: 

Room temperature was 69F

So a meter is 39-3/8" you say, i'm going to have to move my line back 3/8" then. I doubt the impact on readings was more than a few lux though.


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## chevrofreak (Nov 18, 2005)

btw heres a page that lists correction factors for my meter http://www.wattstopper.com/products/related.html?prod_id=4&id=4


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## SilverFox (Nov 18, 2005)

Hello Chevrofreak,

Thanks.

OOOh, a correction factor...  We will have to figure out what to do with that.

Tom


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## yaesumofo (Nov 19, 2005)

I just noticed that my name is misspelled on the list. It's Yaesumofo.
I also wanted to throw in my Meterman Serial number it is 0301139.
I wonder if I should send in this meter to be calibrated before the test.
Here in Hollywood Meter Calibration is important. Gaffers and DP's need to have meters which offer repeatable and identical results when working. In fact I have seen many times where these two coworkers will walk around comparing their meters. in order to determine if in fac their meters are aligned. If there is a difference which meter is off? Attempting to decide which unit will be the standard for the project. I wonder how one of these meters will react if "aligned". Will this throw off the testing results? Do you guys think I should have my meter aligned before my turn to test?
Somewhere I thought I saw an offer of a meterman LM631 which for a fairly healthy premium would be calibrated to an IEEE standard. Have any of you seen one of these?
Do any of you guys have a calibrated meter? How does it compare?

My other comment is that many of the more advanced digital cameras will double as very sensitive and accurate light meters, Have any of you guys experimented in this area?
Yaesumofo


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## SilverFox (Nov 19, 2005)

Hello Yaesumofo,

Sorry about the spelling error... I believe it is now correct.

I think it would be a great benefit to have your meter "aligned" prior to this testing. I would simply add a footnote indicating this and we could see where your numbers fall.

At the end of our pass around, we will send the lights off to a lab for an "official" reading. This would allow you to see how close your alignment is the actual readings.

I had the option to get a NIST certification with my meter. The cost was something like an additional $70. I decided not to get it. I am not sure if anyone has a certification for their meter, but I am sure they will sound off if they do.

Exploring the use of a camera meter as a light meter sound interesting, but I believe it is beyond the immediate scope of this particular project. A future project perhaps...

Tom


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## PeterW (Nov 22, 2005)

Found a link to a company with a number of reference docs about LED measurement and uncertainties, maybe we ought to post the details more widely as it looks useful.

http://www.olinet.com/library.php3

Cheers

PeterW


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## andrewwynn (Nov 22, 2005)

package arrived.. very cool project.. will run the test tonight and send tomorrow.


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## McGizmo (Nov 22, 2005)

Hi guys,

A possible data point to add... I got some sample Nichia 1/2 watt LED's which were measured by Nichia's lab and I was provided with x,y coordinates along with Vf at 150 mA and luminous and radiometric flux measurements. I introduced one of these to my integrating sphere and I measured about 15% more flux, luminous as well as radiometric. So until further information or insight is available, I will be assuming that a closer to truth measure of output will be 85% of what I read with my system. One source of surprise to me was that the sample I tested has a reported Vf of 3.3 but my BK precision regulated power supply showed 3.1 V at the .15 amp level. 

I believe one of the conclusions we will reach when this program runs its course is that we are all in a position to make some reasonable relative measurements and comparisons but in terms of absolute certainty, the level of error is likely significant. 

YMMV is a reality; like it or not.


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## Kiessling (Nov 22, 2005)

Well ... I don't want to be a heretic, but to me a 15% error in our measurements is quite acceptable given the differences in brightness needed to make our eyes realize them at all ...
And who sais Nichia is correct anyway? 
bernie


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## SilverFox (Nov 22, 2005)

Hello Peter,

There is some excellent information in that link. Thank you for suggesting it.

I would recommend that everyone should go through the PowerPoint presentation listed as LED Measurement (P20). It is the last one on the list. I think it gives a good view of the complexities of light measurement.

There are also a lot of other articles that go into detail about the measurement of light. This is a great resource.

Tom


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## SilverFox (Nov 22, 2005)

Hello Don,

In the link that Peter provided, there is a PDF document LED Measurement Instrumentation (R23). It explores the difference between Total Luminous Flux and Forward Looking Flux. It is interesting that the difference between the two is around 15%. I am not sure if it is in the right direction, but if you are measuring Total Luminous Flux and Nichia is measuring Forward Looking Flux, you could be right on.

I wonder if SureFire measures Forward Looking Flux. This could be the source of their conservative ratings...

Tom


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## andrewwynn (Nov 27, 2005)

OK.. done with my measurements.. 






The 'first batch' was done where i normally do my measurements.. but apparently there is a little more wall-bounce that i'd had hoped.. consistantly reading about 2 1/2% higher than when i worked a bit harder to reduce reflected light (second batch). 

of note.. less than 1% error from the initlal turn on measurements to the average of batch 1. 

If you'd like to use the spreadsheet I made to keep track.. it is HERE.. the gray cells are calculated.. only change the black ones. 

My Meter is an el-cheapo.. 'CEM DT-1301'.. the one that you can find on eBay for $50-60 and looks a bit like a paddleball shape. 

Temp in the room was 67F when i did the measurements.. it was also before down so zero ambient light. 

Anything else i'm forgetting? 

I thought it was interesting that my meter reads quite a bit lower than average on the incan.. i guess that bodes well for my 80,000 lux measurement i recently took of the Mag100R.. and my 1D Mag66.. 40,600... and after 3 minutes warm-up.. 40,500.. have to love regulated incan lights.

Since the white led came so close to the average (off by 5 lux.. holy cow).. that bodes well for my more typical measurements of my led lights... I took a measurement quick of my favorite LionCub.. it was 1730 lux with the aged battery and 2070 lux with a brand new one. 

I found it very interesting that my meter reads much higher than the average.. but it looks like that's a bogus number.. there is some odd thing going on like blue being filtered by the lens on some of the meters.. 

Mostly i'm really happy to see my meter is very close to the average for white LED reading.. a little bummed it's not matching the incan so well since i'm doing more and more incan these days. 

Great project. Box will go to Brock on Monday priority mail... just need the address. 

-awr


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## SilverFox (Nov 27, 2005)

Hello Andrew,

Thanks.

You will have to get in touch with Brock to let him know that the lights are headed his way, and to get his address.

Since the purpose of this pass around is to check on how we are currently measuring light, I used your first set of data.  It is interesting to note that the difference that bounce contamination makes is not that significant.

Your data has been added in the first post.

Tom


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## Brock (Nov 29, 2005)

Yup they are on the way to me as I understand it. You guys are quick!


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## andrewwynn (Nov 29, 2005)

yup my 'first set' was the one meant to be included.. because even with the 3% error it's just much easier to measure the way i usually do. 

My 'measurment spot' is on the corner of a door jamb.. i align with the corner.. and go out like 5" away at a 45 deg. angle.. 97% (apparently) of the reflected light goes off away from the meter but it gives me a nice close reference line i can line up with really easily (i have a permanent mark like a 40 3/8" tall kid marked their spot).. (the extra inch is 'cause my meter is 1" thick). 

So.. i was at the PO yesterday and ready to send the box when i realized that because it is over a pound (well i think it measured exactly a pound but 1# is the same as 1.99# as far as the PO is concerned.. it adds complication.. plus there are a LOT more people this thing is going to so i came up with a really nice idea to keep the shipping box from getting ratty as hell.. 

Use a brand new free one each time.. I took it home and cut down the foam block to exactly fit the inside of a #5 Priority mail box.. it now weighs less than a pound and you can print your postage with insurance and free tracking number at home.. i just use spray adhesive to glue the label/postage onto the boxes.. 

Anyhow sorry that it delayed an add'l day but it will make it much smoother going for everybody else.. just get 

Item No: O-1096L 
Priority Mail Box
Large 9.25" x 6.25" x 2"

My PO calls it a #5 box.. if you don't have the box you can still pre-print the label with postage and when you go to the PO just stuff it in the box.. it has self-sealing tape, and they will usually tape the label on for you.. 

So.. now each person gets a nice clean new box and you can just hand to your mailman to ship or drop in a PO drop box (post 911.. not allowed to drop items 1# or more).. coincidentally the max for self-insuring is $500.. very convienent. 

Off to brock today should get it tomorrow... he lives only 3 1/2 hrs away. 

-awr


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## Brock (Dec 1, 2005)

Got it today, I live in the sticks. Of course I work until 11 tonight. Can't wait to tear it open...


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## Brock (Dec 2, 2005)

Uh oh. Just got home about 30 min ago, ya it's 2am here, all the lights are frozen since its 15F outside and they sat in my car all day.

Anyway after 30 min set out to warm them up I tried them, they were still cool, but just had to play before going to sleep and the A2 lamp is out. I didn't take it apart of do anything yet just in case I missed something as to why it isn't coming on. By looking at it I can see why some have said the beam was oblong, the lamp isn’t vertical in the housing, not sure if it was like that the whole time or maybe it got bumped enough in this last trip.

So I have spare A2 lamps, but that would likely throw things off from here on. I will go to sleep and check back when I get up.


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## andrewwynn (Dec 2, 2005)

I didn't notice anything funny about the lamp but i thought i did remember it not having that round a beam.. When i got my first hotwire light.. the bi-pin bulb was bent like 30 deg.. they really must have dropped that package hard for that to happen. I don't think it would be that big of a deal to exchange the bulb... especially if you happen to have a meter that matched somebody elses (model, make) to get some idea if there is an offset... interesting problem though i suppose. 

-awr


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## SilverFox (Dec 2, 2005)

Hello Brock,

Ah, another variable... Cold effects.

The A2 beam is a bit oblong. I am not sure why it would not work in the cold, unless there is something with the circuitry that is sensitive.

When Don and I put this project together, we understood that a weak point was the lamp in the A2. I really expected it to last throughout the entire first round of testing. I feel that there is close enough quality control on the SureFire lamps that a replacement lamp should not effect our measurements drastically. I may have to give SureFire a call and complain about poor lamp life.

An Ohm meter should verify the condition of the lamp. If it is bad, just replace it. If you end up replacing it, you will have to run a set of batteries through it to "age" it a bit. I hope this will bring it close to where the old lamp was in terms of output. I will make sure you get another lamp to replace yours.

Let us know how you make out...

Tom


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## wquiles (Dec 2, 2005)

SilverFox said:


> When Don and I put this project together, we understood that a weak point was the lamp in the A2. I really expected it to last throughout the entire first round of testing. I feel that there is close enough quality control on the SureFire lamps that a replacement lamp should not effect our measurements drastically. I may have to give SureFire a call and complain about poor lamp life.



I have at least 20 cycles of 20-25 minutes (each on fully charged MP700 4.2 rechargables) and my A2's lamp looks to my untrained eye as white now as it did several months back when I got it. I really love my A2's regulated lamp 

Will


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## Brock (Dec 2, 2005)

I will ohm it out when I get home and if it is bad replace the lamp and let in burn for a set of batteries. It is weird if it is the lamp, packaged like that it would take quite a jar and I have dropped my A2 on concrete a few times without any issues.

I just hope it is just the lamp…


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## Brock (Dec 4, 2005)

It's not the lamp. I can't for the life of me find my A2, I thinks it sin my wifes van and I ahve been working 12's the last couple of days.

But it's not the lamp. It almost looks like the contact point at the base of the head is depressed, but I wanted to check mine to see if that is normal.


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## andrewwynn (Dec 4, 2005)

got a small magnet to put on the top of your cells? that is bizarre.. hope it's just a misfit of the 123s you have or something.. i never bothered to look closely 'cause it lit right up when i tried it.. you have a way to apply voltage outside the batteries (bench supply, etc? ).. 

-awr


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## Brock (Dec 4, 2005)

I will try external power tonight, I will feel like an idiot if it is the cells and one was just squished a bit. I did try all three in the alph and all worked fine.


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## SilverFox (Dec 5, 2005)

Hello Brock,

I was in touch with Don today. He suggested that you should try to eliminate the switch. If the switch is the problem, we will get another one headed your way.

If the problem persists, Don suggested that you send the A2 to him and he will get it working again and ship it back to you.

Please understand that while we were trying to keep this project moving along, things happen and sometimes we just have to take a little break. I know you are very busy. Please don't let this project add to your pressures. This is supposed to be fun.  It is perfectly acceptable to take a few days and figure out what is going on when you have some breathing time.

Tom


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## Brock (Dec 5, 2005)

Thanks!

If I can find my A2 it woiuld make sussing it out a lot easier.

Hopefully tonight


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## Brock (Dec 6, 2005)

Ok start laughing. 2 new SF 123's and all is well. I had been using 4 Duracell ultras and somehow all 4 have slightly indented tops so they were just short enough to not make contact.

The package is on its way to N162E.

The thing that amazed me was how low the Blue UV read on my old meter. I will get the results to you sometime


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## chevrofreak (Dec 6, 2005)

I would like to mention that for the last 6 months or so my light meter has been mounted and sitting on my table with the sensor uncovered, it seems that this may have somehow gradually caused the readings to increase. Since I've been putting the sensor away after each use my readings have been coming down to where they should be.


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## SilverFox (Dec 6, 2005)

Hello Brock,

Glad you got things figured out.

Tom


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## SilverFox (Dec 6, 2005)

Hello Chevrofreak,

Most interesting observation... I wonder what is going on. 

As far as I know, the light meters use a silicon photo diode, I wonder if their properties change depending on constant or intermittent use...

Tom


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## N162E (Dec 9, 2005)

Test Lights are here, just delivered. Barring any unforseen circumstances I will do my readings tonight and pass the package on to WPTSKI tomorrow. Oh, by the way, yes the A2 works fine. The package and packaging are in perfect condition. 
Nice job on the foamwork. :goodjob:


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## SilverFox (Dec 9, 2005)

Hello Fred,

Have fun... 

Tom


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## N162E (Dec 10, 2005)

For the sake of time I am going to be real brief now and elaborate more later.

My meter is an Extech 401036 SN 020904868 purchase Feb. 02. Mine is not Nist traceable. Room temp is 71.2. All results are the average of three readings, lights and heads were rotated in order shown. Max hold feature on this meter made taking readings a snap.

A2 2387
WT 1148
GR 2340
RD 1916
BL 65

More later.


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## wptski (Dec 10, 2005)

Okay, I got the hand off from N162E(Fred) plus a couple of burgers too! Fred, the onions are still coming up! 

On to the test. I used a MeterMan LM631, #0401299 and the test temperature in my basement was a cool 64.5F. Sanyo CR123A cells which measured 3.24V before the test. After the test, the two in the A2 measured 2.94V and the other cell was 2.86V.

The three test average:

A2->2333
WT->1147
BL->245
GN->2523
RD->1146

I forgot to look before posting but I think that my blue test is higher than most!

I put a fresh set of AAA's in my meter and when I rechecked the Sanyo cells, I also checked the AAA's. One of the Novacells was bone dead, zero and the others read 1.5V!! Not sure how/if this would have skewed the test but I'm going to try a test tomorrow with both sets to see what difference that would make. The LM631 does have a low battery indicator. Maybe with one dead cell, it's still accurate!

EDIT: Nope my blue test isn't higher at all!


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## wptski (Dec 13, 2005)

Lights shipped to JTR1962!


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## SilverFox (Dec 13, 2005)

Hello Bill,

Thanks.

I have added your and Fred's data to the first post. I will have to get after Brock to get his data...

Tom


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## wptski (Dec 13, 2005)

SilverFox said:


> Hello Bill,
> 
> Thanks.
> 
> ...


Tom:

Did you use invisible ink? I don't see my data!


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## SilverFox (Dec 13, 2005)

Hello Bill,

You Meterman is moved up with the other Meterman numbers. I believe yours is serial # 0401299.

Tom


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## wptski (Dec 14, 2005)

SilverFox said:


> Hello Bill,
> 
> You Meterman is moved up with the other Meterman numbers. I believe yours is serial # 0401299.
> 
> Tom


Tom:

Yep that's my LM631 but it wasn't listed when I looked after I read your post but it is now! Wonder why the Edit Date/Time at the bottom of your post is three days old?

BTW> I reinstalled the old set of batteries in my LM631 of which one was bone dead. No low battery icon and lux reading is about 25 higher compared to fresh batteries!! Isn't that odd?


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## SilverFox (Dec 14, 2005)

Hello Bill,

When I update the graphs, I do not have to edit the post. I just post new graphs in PhotoBucket and the graphs show up as updated in the post. The last edit to the post was to indicate that Brock, Fred, and you had finished the testing.

We will have to get the electronic circuit experts to figure out what is going on with your meter. On the surface, I would expect different readings when the driving voltage is cut in half. I would also expect your low battery alarm to trip. 

I am glad you check your batteries, and everyone else should keep this in mind and check their meter batteries before testing.

Tom


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## wptski (Dec 14, 2005)

Okay, makes sense now.

You'd think that with one dead battery, the voltage would be low enough to trigger a low battery alarm but I guess not! That being, it would be a good unit to use rechargables in, if one used it that much.


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## N162E (Dec 17, 2005)

SilverFox said:


> Hello Bill,
> 
> I am glad you check your batteries, and everyone else should keep this in mind and check their meter batteries before testing.
> 
> Tom



I checked mine before testing also. The main battery (9 Volt) and the memory battery (Coin cell) were BOTH very low. I did not think to test with the low batteries to see if it made a difference.


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## jtr1962 (Dec 18, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Here's my results

*K2 red* 2840, 2780, 2760 average: *2793* _battery(start, end):3.284V, 2.889V_ 
*K2 green* 1915, 1907, 1908 average: *1910* _battery(start, end):3.013V, 2.863V_
_**_*K2 blue* 1055, 1047, 1045 average: *1049* _battery(start, end):2.954V, 2.883V_
*K2 white* 1141, 1139, 1134 average: *1138* _battery(start, end):2.944V, 2.854V_
*A2 incan* 2530, 2520, 2530 average: *2527* _battery(start, end):3.263V+3.267V, 2.898V+2.907V_


Room temperature: _72.1°F_
Light meter: *CEM DT-1300*

My test setup seems to be very repeatable. For all tests I waited 2 minutes or longer before taking readings. I left the lights running while I broke my test setup down and set it up again. Overall the lights were on about 5 minutes total. It's interesting to note that the second two readings for the red dropped the most since red is most affected by heat. The others dropped slightly. The A2 was most consistent but that's to be expected as incandescents aren't affected much by a hotter flashlight body.

I'll see if I can make a jig and get some lumens tests for some or all of the LED lights later today. I won't try with the A2 since any extra run time would cut into its relatively short life.

I should be sending these out to the next person Monday or Tuesday.


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## jtr1962 (Dec 18, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

BTW, I didn't look at anyone else's results until after I posted mine so as not to be prejudiced. Most of my results seem within the range of everyone elses but I'm sure the red result will raise some eyebrows. Thinking that maybe I did something wrong, I just went downstairs and repeated the measurement. I got 2850 lux without allowing warmup. That's not much off my first reading allowing 2 minute warmup. I guess my light meter is just very sensitive to red.

The results for white light so far seem pretty tight. Not surprising since that's what our meters are calibrated for. A meter could be not have a CIE response at all yet still be accurate for most types of white light. Obviously it will off with sources having "spiky" spectrums, or narrow-band sources like LEDs.


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## jtr1962 (Dec 18, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

I did some lumens tests. My setup is really designed to deal with 5mm LEDs so it was marked in 5 degree increments. I probably would have needed something with one degree increments plus a much greater distance between the light and the light meter in order to get more accurate results. Nevertheless, here are my results:

K2 white: 59.3 lumens
K2 red: 88.5 lumens
K2 green: 62.2 lumens
K2 blue: 55.1 lumens

If I correct by the ratio of my lux readings to the average so far I get:

K2 white: 56.3 lumens
K2 red: 50.9 lumens
K2 green: 69.9 lumens
K2 blue: 35.1 lumens

McGizmo's results using his integrating sphere:

K2 white: 51 lumens
K2 red: 48 lumens
K2 green: 52 lumens
K2 blue: 14 lumens

It looks like on average our light meters are highly over sensitive to blue and somewhat over sensitive to green. My corrected red and white results come pretty close to Don's. I'm sure with a better setup I would have done better.

Spreadsheets


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## SilverFox (Dec 18, 2005)

Hello JTR,

I guess the batteries worked out OK...  

Do you happen to have an IR LED? I wonder if your red sensitivity may be coming from the cut off value of the filter inside your meter. I noticed one of my meters is more sensitive to IR than the other.

Tom


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## jtr1962 (Dec 18, 2005)

SilverFox said:


> Hello JTR,
> Do you happen to have an IR LED? I wonder if your red sensitivity may be coming from the cut off value of the filter inside your meter. I noticed one of my meters is more sensitive to IR than the other.


Everyone's house has IR LEDs in things like TV remotes. Anyway, the business end of one of my remotes gave quite a response to my light meter when it should have given zero. Evidently then that explains my high red response. Now the meter isn't too badly off with white light, so I'm guessing the response to some other color is less to compensate. Since the meter grossly over responds to blue also perhaps the green response is less than it should be, especially in the yellow-green area. It would be nice to have ultra-narrow band emitters in a whole range of colors to check.

Aren't our light meters such precision instuments?


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## jtr1962 (Dec 19, 2005)

*Re: Light Meter Benchmark Testing – CPF style*

Lights sent to rdshores today.


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## SilverFox (Dec 26, 2005)

Update:

Jtr's results have been added to the charts in the first post.

I made a mistake during my average and standard deviation calculations. For some reason, I was not including the first few data points. That has been corrected.

I decided to group the meters together by manufacturer. I am not sure if this helps, but it may allow us to see differences better. We we get down to the final analysis, I will tidy things up, but for now this should do.

Tom


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## Kiessling (Dec 26, 2005)

Thanx for the hard work guys !!!! :thumbsup:


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## SilverFox (Jan 10, 2006)

Update:

On 12/19/05 JTR mailed the lights to RDShores. That is the last information we have.

RDShores has not posted since 12/15/05, and I don't know where he, or the lights, are. The Post Office has informed me that I can not make a claim on the insurance until 14 days have passed, which will be this Friday. Unfortunately, we did not ask for delivery confirmation, so we have no way of tracking the package.

Bernie sent RD an email asking him to contact me, however I have not heard from him.

Anybody know RDShores, or live in Vermont?

Tom


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## Kiessling (Jan 10, 2006)

This is bad. If the reference lights are lost the experiment will stop here, right?


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## cy (Jan 10, 2006)

bummer :green:


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## HarryN (Jan 10, 2006)

Kiessling said:


> This is bad. If the reference lights are lost the experiment will stop here, right?


\


Hopefully not. The point of insurance is to make sure we can replace the reference lights with new ones should they become lost. Of course, there is the slight problem that we will have to repeat some of the earlier work, but that should not be a surprise to technologists.


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## Kiessling (Jan 10, 2006)

Yeah ... I was talking about loosing the results we have gathered so far ... 
But let's see ... can't we just send a letter to the address we shipped the lights? Just in case ...


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## wptski (Jan 11, 2006)

This reminds of a problem I ran into on eBay! I was the winning bid but the seller wasn't replying after the PayPal payment was sent. Turns out that the person had to be rushed to the hospital for a emergency! It took several weeks but it all worked out. Maybe this could be along the same lines? Heaven forbid that the person has passed as there would be little chance of a family member if any knowing anything about this project!!

The biggest lose would be the time spent already.


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## SilverFox (Jan 11, 2006)

Update:

I have bad news...

On 12/31/05 Robert D "Bobby" Shores suddenly passed away...

I am trying to contact the surviving family about our test lights. 

Tom


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## bwaites (Jan 11, 2006)

Most definitely tragic news.

A loss of a member, bag the lights except as an afterthought!!

News:

http://www.caledonianrecord.com/pages/community_deaths/story/c97411589

Bill


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## chimo (Jan 11, 2006)

This is very sad news about Bobby's passing. May he rest in peace.

Paul


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## jtr1962 (Jan 11, 2006)

This is terribly tragic, especially the suddenness of it. When I PMed Rob about sending the lights he gave no indication that anything was wrong. When we received no word from him I thought he might be ill, but it didn't even occur to me that he had passed. My deepest condolences to his family.


----------



## wquiles (Jan 11, 2006)

Oh my God!. What a terrible thing to learn about his death while trying to locate the lights . No wonder we never heard back from him. 

I hope he at least died peacefuly and with dignity.

Will


----------



## cy (Jan 11, 2006)

sorry to hear the bad news :green:


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## NextLight (Jan 11, 2006)

New owner of an LM631, SN 0507003, following the results with interest. Mine also shows some IR sensitivity, but ONLY to my Dish Network IR/UHF Pro Remote.

Would be interested if there is the opportunity to join the testing, if it is restarted or continued.

Thanks.


----------



## SilverFox (Jan 30, 2006)

Update:

I don't have much news, however I was able to get in touch with Bobby's dad. He told me his daughter is taking care of Bobby's things, and I should talk to her. I have been trying to get in touch with her and have left several messages, but I have not heard back from her. He did tell me that she had mentioned that I had called, so there is some communication going on.

I'll keep trying to get in touch with her...

Tom


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## SilverFox (Jan 30, 2006)

Hello NextLight,

I would be happy to add you to the list, however we need to get the lights back first. Remind me again, once we have the lights back and are continuing with the testing.

Tom


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## SilverFox (Jan 30, 2006)

Another update:

I just got off the phone with Bobby's sister. I directed her to this thread to see what the lights look like. She thinks she may have seen them, but things are in a bit of confusion. She will be getting back to me in the next little while and will spend some time searching for them.

I have instructed her to ship the lights back to me and we will pick up from there.

Tom


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## SilverFox (Feb 3, 2006)

Update:

I have good news, and more good news...   

First the good news... Bobby's dad remembered a package that had some lights in it, and found our lights. Thank you Robert!!!

And more good news... Bobby's sister sent me the lights and I have them now. Thank you Sherri!!!

We are back in business.

I see that Doug (Quickbeam) is the next on the list. I will get in touch with him and send them his way.

We owe several people in Vermont a big thanks for helping us figure out where these lights went and especially those that were involved in getting them back to us. Someday I will fill you in on all the details...

Tom


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## McGizmo (Feb 3, 2006)

Great news Tom! Thanks for your efforts here!! :thumbsup:


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## Kiessling (Feb 4, 2006)

:thumbsup:
And thanx for those kind folks, too.
bernie


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## cy (Feb 4, 2006)

great news...... really looking forward to seeing these test lights. 

thought Doug (quickbeam) is taking some time off from testing


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## SilverFox (Feb 8, 2006)

Update:

The lights are on their way to Doug (Quickbeam).

Tom


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## wptski (Feb 8, 2006)

Tom:

Good work and many thanks goes to Bobby's family for helping us continue this project without going back to square one again!


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## N162E (Feb 8, 2006)

SilverFox said:


> Update:
> 
> The lights are on their way to Doug (Quickbeam).
> 
> Tom


This is really good news. Looking forward to results starting to roll in again.


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## SilverFox (Feb 9, 2006)

Update:

I sandwiched in NextLight after Archangel.

Tom


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## SilverFox (Feb 11, 2006)

Update:

Doug (Quickbeam) asked me to post his results.

Ambient Temperature: 70 deg. F.

Cen-Tech FX-101 Model #41728 Serial 037090

A2 Incandescent = 2420
White LED = 1250
Blue LED = 301
Green LED = 2770
Red LED = 1027

Qups readings with the lightbox with the same meter
for reference for folks who make their own:

A2 Incandescent = 4200
White LED = 3250
Blue LED = 800
Green LED = 3400
Red LED = 1770

EDIT: Please note that you need to divide these Qups numbers by 100 to correlate to Doug's overall output numbers on his web site. END EDIT

Extech Datalogging Light Meter Model #401036 Serial #040403597/G023796

A2 Incandescent = 2340
White LED = 1187
Blue LED = 69
Green LED = 2510
Red LED = 1695

This meter is never used for Qups readings.

Thanks Doug.

The lights are now on their way to jtice.

Tom


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## SilverFox (Feb 11, 2006)

Update:

The data from Doug's two meters has been added to the first post.

Tom


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## jtice (Feb 13, 2006)

I got the Test Package today.

Big thank you goes out to SilverFox, PK, and McGizmo for making this all possible !!!!!! :buddies:

NOTES:
- Light Meter Used= Meterman LM631
- New Surefire 123 cells used. Measuring 3.177V
- Testing done under my ussual Runtime conditions. Room only lit by monitors and TV.
Light Meter never reads more than 2 Lux Baseline.
- My LM631 imediately reads 40 Lux as soon as the Peak Hold function is tunred on.
- I am half blind as a result of this test.









P.S. I need the address of the next person in line please.

~John


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## jtice (Feb 13, 2006)

OK, now that I have posted, and then compared mine to the average readings in the first thread.

.... I am Concerned !!!!! .... for Everyone !!!! :huh2:

I am seeing WAY too much of a difference in readings.
This is very concerning, we toss around lux readings here on a daily basis, 
and while we all know there are going to be discrepences, but these are far enough off for us to change our minds about how much we trust and rely on them.

If our lux readings are this far off, imagine the runtimes.
In runtimes, you have to remember, dont pay that much attention to the Lux numbers.
The runtime curve is whats important.
When a runtime is setup, and the light is turned on, there is no time to line it up perfectly.
I basically try to line it up like im sighting a gun, and get it the best I can.
But chances are, if I was going for peak Lux, taking time to aim the light just right,
I would most likely get a higher reading, than what my runtime starts out at.

~John


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## SilverFox (Feb 13, 2006)

Hello John,

You will have to PM KiteLights to get his address.

I also need the serial number from your Meterman, and the ambient temperature during the testing.

I don't know what is wrong with your peak hold function... but I will be using the manual peak numbers.

Tom


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## jtice (Feb 13, 2006)

Tom,

Light Meter LM631 Serial #: 0404194
Temperature is 73 Deggres F.

I am not sure what the deal is with the Peak hold either,
its always done that, but it woould make it further off if it didnt do that. :shrug:

Ill PM KiteLights, thanks
~John


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## wquiles (Feb 13, 2006)

If it makes you feel any good, the peak function on my LM631 has "never" worked at all. I always get more consistent readings in manual mode and the peak function 100% of the time measures lower values 

Will


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## SilverFox (Feb 14, 2006)

Hello John,

At the end of the round of testing, I am planing to send the lights in to have them checked with "standardized industrial" meters. You can then adjust your results according to the "real" results, and be able to offer an improved "guess" as to what the lux values are for lights you are checking out.

The ideal situation would be having everyone equipped with $3000+ light measuring equipment, but my budget is a little short for that...

I have been listing the test results by meter manufacturer in the table. At the end of the testing, perhaps we well be able to observe if one manufacturer is more consistent than another.

At the very least, when I report that my light puts out 100 lux more than your light, you can simply say "So What." 

Tom


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## wptski (Feb 14, 2006)

I've never used the Peak Hold on my LM631 either! I'll tell you one thing though. When I got to the third round of the test, I had enough and was seeing spots for hours!


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## jtice (Feb 14, 2006)

lol my eyes were going nuts alot,
especially after staring at say, green, then swithing to red, eekk :green:

well,, i guess, its good to hear no ones peak hold works well... :thinking: :shrug:

~John


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## Kiessling (Feb 14, 2006)

I always use the peak hold as it is way more convenient than manual mode which is too unstable IMHO.
bernie


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## N162E (Feb 14, 2006)

jtice said:


> well,, i guess, its good to hear no ones peak hold works well... :thinking: :shrug:~John


Mine works great and I wouldn't think of trying to do it any other way. I would check my batteries first and if that was not the problem return it to the manufacturer for service. Peak hold not working could be a problem that is affecting all of your readings.


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## CroMAGnet (Feb 14, 2006)

Just curious if this pass-around has gone through NorCal yet? 

BTW I get the same results as Quickbeam most of the time. I guess it must be because we have the same brand of LUX meter. or at least it looks like it from the one pictured on his website.


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## SilverFox (Feb 14, 2006)

Hello CroMAGnet,

If you check the first post you will discover that there are 13 people ahead of you, but you are still on the list. We haven't forgotten about you, we just got delayed for a short while.

Tom


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## cy (Feb 14, 2006)

just checked first post for results so far.

good grief! deviation is enormous,,,


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## CroMAGnet (Feb 15, 2006)

Thanx! OIC... The spread on the colored LEDs is all over the board but the white LEDs and incan are reasonable.

If you take out the highest and lowest Lux reading you get a spread from approx 200 LUX from 1000 - 1200 LUX That's not bad for all the different meters and people involved.

I have been wondering something for a few months now. Actually, ever since the start of this thread. From what point do you measure the 1-meter? From the tip point of the white dome to the lense of the flashlight? or from the tip of the dome to the LED/BULB?? Have you guys established this yet? 

.


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## wquiles (Feb 16, 2006)

CroMAGnet said:


> Thanx! OIC... The spread on the colored LEDs is all over the board but the white LEDs and incan are reasonable.
> 
> If you take out the highest and lowest Lux reading you get a spread from approx 200 LUX from 1000 - 1200 LUX That's not bad for all the different meters and people involved.
> 
> ...


I personally find it 100% impossible for each one of us to align/hold the meter exactly the same, at the same distance, over and over again for each test/light. Couple that with the large number of variables (including the meter itself), and it is not surprising the large spread we have seen so far. 

We will have to apply standard statistical math to these results to try to come up with some reasonable values. Throwing away the higest and lowest is most definitely a great place to start 

Will


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## SilverFox (Feb 16, 2006)

Hello CroMAGnet,

The test procedures are also listed in the first post. If you go back to it and carefully read it, I think most of your questions will be answered.

The deviation is high, but I am waiting to see some calibrated results to see where we stand. I agree that we may have to toss some of the numbers, but it still is interesting how everything is turning out. There may be a pattern, if we look hard enough.

Tom


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## HarryN (Feb 17, 2006)

I suspect that the answer is in the plot by evan9162 in post # 230. The data is bi or possibly tri nomial. This is a pretty normal concept in product performance.


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## SilverFox (Feb 18, 2006)

Update:

John's data has been added to the first post.

Hopefully he has been able to make contact and mail the lights to KiteLights...

Tom


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## jtice (Feb 18, 2006)

Yep, the lights are on their way to kitelights. 
and I sent him the tracking #

~John


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## kitelights (Feb 20, 2006)

jtice said:


> Yep, the lights are on their way to kitelights.
> and I sent him the tracking #
> 
> ~John


Received lights - been gone for the weekend. I'll test tonight.

John or Tom - I'm not able to PM and Codeman's CPF email is turned off. Would one of you contact Codeman and ask him to email me with his address?

[email protected]

Thanks-
Ken


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## andrewwynn (Feb 20, 2006)

nice to see this project chugging along.. quite a story to have one of the people yikes up and die in the middle of the project.. with as many members of cpf, it's inevitable something like that will happen, but yikes nonetheless.

-awr


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## jtice (Feb 20, 2006)

I sent a PM to Codeman for you kitelights.

~John


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## Codeman (Feb 20, 2006)

Thanks, John. Email sent to Ken.


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## SilverFox (Feb 24, 2006)

Update:

Kitelights is having problems posting... he sent his information to Codeman, who is also haveing problems posting. Now it is my turn... 

From Kitelights

_The lights were sent to Codeman Wednesday AM (2-22).

Meter was a Meterman LM631 #0206354. I checked the cells in the meter
(original) with a Radio Shack battery tester and they were good, but I
changed them out with fresh cells (tested those too).

My three CR123s were Surefire and they tested well on the battery tester.

Setup was performed in a bathroom. I always use this room for testing
because it is the only room that I have that doesn¹t have a window. Room
temperature was 72 degrees.

I used a tripod setup with the rear leg long so that the front two legs 
were perpendicular to the floor (tripod was set up in a leaning position) and it
was setup over a black bathroom rug. I attached the lights to the tripod
facing downward towards the floor with the Meterman on the floor facing
upwards. I measured one meter between the sensor and the edge of the bezel
and checked the distance often using a precut carbon fiber kite spar. I¹m
confident that the distance remained consistent during the test within
one-eighth inch.

I did not use the peak hold function - It¹s easier for me to find center by
watching the display show increasing and decreasing numbers. All readings
were taken after a minimum of two minutes on time and 5-20 minutes between 
each test. I did not record numbers that I could not maintain with the tripod.

Aleph I

White 1240 1230 1210 average 1227
Blue 230 233 235 average 233
Green 2640 2650 2650 average 2647
Red 1140 1130 1160 average 1143


A1 2250 2360 2400 average 2337


I suspect that I would have had less difference with the A1 if I had
increased the on time.

Another note - For whatever reason, I actually took five readings on the
white Aleph I and the last three readings were identical; however I 
recorded the first three readings.

I¹ve learned quite a bit from this thread. If nothing else, how meaningless
many of our measurements really are. I do think we¹ll find some limited
applications that are at least useful for reference.

This was also my first time to see and use an A1, Aleph, U bin luxeon and a
R, G and B luxeon.

Thanks to Don and PK for the contributions, Tom for all the work putting
this together and keeping it going, and the great input and info from many
of the CPF geniuses._

I hope this works...

Tom


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## Codeman (Feb 24, 2006)

Thanks, Tom. Either CPF had a gremlin this morning, or something has changed and I need to adjust my firewall settings for CPF on my home computer.


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## SilverFox (Feb 24, 2006)

Update:

I have added Kitelights data to the graphs in the first post.

Tom


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## Codeman (Mar 1, 2006)

I received the lights this morning and will complete my testing by this weekend.


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## Codeman (Mar 8, 2006)

Due to some health issues the last few days, I was not able to complete testing. Which I hate, but I didn't want to delay everyone else further.

The lights were sent to 4sevens today.


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## SilverFox (Mar 9, 2006)

Hello Ray,

Sorry to hear this. Would you like to be put back on the list for testing at a later time?

Get well soon.

Tom


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## Codeman (Mar 9, 2006)

Tom, if you can add me to the end, that'd be great. I've been absolutely laid out with what my doc thinks is an intestinal parasite. Things seemed to be on the upswing now, but this isn't something I'd ever want to go through again. Over the past 4 days I've lost 16 lbs.


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## Kiessling (Mar 10, 2006)

:sick2: ... this seriously sucks! If there is one infection I truly find uncomfortable to even think about, it is those pests. Good luck and hang in there!!!!! 
bernie


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## 4sevens (Mar 18, 2006)

Done! I need Wquiles's address. PM incoming

My peak repeatable results in lux at 39 and 3/8in
luxIII 862
blue K2 825
green 1299
red 2390
a2 2300

68 deg F ambient


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## wquiles (Mar 18, 2006)

PM replied. I am definitely looking forward to see how my meters compare to the ones posted already 

Will


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## SilverFox (Mar 18, 2006)

Hello David,

Thanks, I will get your results up later today.

Tom


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## andrewwynn (Mar 18, 2006)

what a great project.. i love when a new post brings this to my attention.. it's great to see my meter pulling in so close to the nominal, especially for the whites. 

-awr


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## SilverFox (Mar 18, 2006)

Update:

I have added Davids results to the first post.

Since Brock lost the piece of paper he wrote his results on before he could report them, and since Codeman "fell a little under the weather"  when it was his turn, I have rearranged the schedule slightly to allow them an opportunity to add their valuable contribution to this project. 

Check the first post for the schedule changes.

Could it be that we are beginning to see a trend in the data?

The Red, Blue, and Green LED readings are still bouncing around, however it almost appears that there is a slight downward slope to the Incandescent and White LED readings...

Keep in mind that the graph shows the data in chronological order, while the table shows the data by meter type.

Interesting...

Tom


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## evan9162 (Mar 18, 2006)

Here's the LM631 data graphed:







There's definitely two distinct response curves that correlate nicely with the white LED reading.

Here's the raw data, sorted by serial number:






A definite break at 04/01-04/04


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## N162E (Mar 18, 2006)

Excellent use of data Evan. You have to wonder if the manufacturer is even aware.


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## wquiles (Mar 20, 2006)

SilverFox & 4sevens - the lights safely arrived today 

I expect to be done and have the units shipped to the next person (cy) in line by Friday or Saturday at the latest 

Will


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## wquiles (Mar 23, 2006)

I am done. Package ready to leave to cy tomorrow Friday. I will post my data in the morning (two light meters as well as my "Light Box").

Will


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## cy (Mar 24, 2006)

looks like I'm up next


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## SilverFox (Mar 24, 2006)

Hello Will,

Great.

I am looking to what you found with your light box.

Tom


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## wquiles (Mar 24, 2006)

cy said:


> looks like I'm up next


Package hand delivered to the Postal Office this morning. I already sent you via PM the tracking/insurance #, so please let us know when you get it 

Will


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## wquiles (Mar 24, 2006)

Tom, here is all of the data that I collected this last week:

Test #1 - Meterman LM631 Light Meter, Serial 0503014
Recorded on 3/21. Temperature 61F

Light=Measurement ([email protected]) #1/#2/#3=Average
A2=2200/2260/2230=Ave=2230
A1 White LED=836/850/854=Ave=847
A1 Green LED=1279/1298/1286=Ave=1288
A1 Red LED=2370/2340/2420=Ave=2377
A1 Blue LED=823/817/820=Ave=820


Test #2 - Lutron LX-102, Serial Q030770
Recorded on 3/23. Temperature 53F

Light=Measurement ([email protected]) #1/#2/#3=Average
A2=2520/2540/2490=Ave=2517
A1 White LED=1211/1147/1193=Ave=1184
A1 Green LED=2670/2650/2670=Ave=2663
A1 Red LED=1580/1600/1570=Ave=1583
A1 Blue LED=760/750/750=Ave=753


Test #3 - wquiles' "Light Box", Serial 001, as shown here 
Light meter used = Meterman LM631 Light Meter, Serial 0503014
Recorded on 3/23. Temperature 76F
Note that the Light Box measures reflected light only
Light=Measurement (on LBU's, Light Box Units) #1/#2/#3=Average
A2=560/570/572=Ave=567
A1 White LED=298/289/293=Ave=293
A1 Green LED=230/233/234=Ave=232
A1 Red LED=630/630/627=Ave=629
A1 Blue LED=175/174/177=Ave=175


Test #4 - wquiles' "Light Box", Serial 001, as shown here 
Light meter used = Lutron LX-102, Serial Q030770
Recorded on 3/23. Temperature 76F
Note that the Light Box measures reflected light only
Light=Measurement (on LBU's, Light Box Units) #1/#2/#3=Average
A2=570/567/578=Ave=572
A1 White LED=395/398/398=Ave=397
A1 Green LED=427/426/425=Ave=426
A1 Red LED=353/351/351=Ave=352
A1 Blue LED=39/39/38=Ave=39 => Note value is way too low. I did several times, but always got this range. Don't know why 

Will


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## wquiles (Mar 24, 2006)

Here is a graph of the data that I captured:





Note that my two meters treat red and green opposite. Red gets higher values on the Meterman and Green gets higher values in the Lutron. Which meter is right?   

Will


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## SilverFox (Mar 25, 2006)

Hello Will,

Thanks. I have added your data to the first post.

To answer your question, perhaps both are wrong and the real value is somewhere in between... :nana:

Tom


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## Kiessling (Mar 25, 2006)

There are some disturbing differences that have shown up over the course of the testing ... :green:
bernie

P.S.: thanx again for all involved for the very hard work !!!


----------



## HarryN (Mar 25, 2006)

We actually have enough data to begin some more detailed statistical analysis. I have forgotten most of what I used to know about this; however, if you plot ALL of the data for the white LED lights and white A2 (on 2 different graphs), you can obtain some kind of distribution.

If you have a meter with a mean reading outside of the 2 sigma region, you can start making reasonable assumptions that the meter (compared to the rest of the group) is providing unreasonable results.

If your meter's average reading is within 1 sigma of the mean, your meter readings are considered to correlate well.

Tom, I see your comment about a slight downward trend in the readings. It would be easier to see if this is real if we plot a full data set over time on an SPC chart.


----------



## cy (Mar 31, 2006)

Ok, just finished readings... got spots in my eyes! can barely see the monitor :green:

LM631 #0503011 
room temp 69 degrees

1. UX1J = 1013, 973, 955 = 9803 
2. Blue = 1013, 1004, 1009 = 1008
3. Green = 1543, 1525, 1502 = 1523
4. Red = 2430, 2310, 2420 = 2386 
5. A2 = 2240, 2320, 2340 = 2300

Ready to ship off to next person. Please PM with shipping info.


----------



## SilverFox (Mar 31, 2006)

Hello Cy,

Your measurement of 9803 for the White LED seems a bit off, would it be OK to round it off to 980?  

You will have to get in touch with Archangel for his shipping information.

I will try to get your data added to the data in the first post.

Thanks.

Tom


----------



## wquiles (Mar 31, 2006)

cy said:


> Ok, just finished readings... got spots in my eyes! can barely see the monitor :green:


Good! - once I shipped them I never heard back from you so I was beguining to worry the package was lost. Glad to hear you got everything OK 

Will


----------



## cy (Mar 31, 2006)

tom, feel free to round off all info 
thanks again for tracking all this. 

OT, got all sorts of li-ion cells if you need any more cells. 

Pkg will be enroute to archangel. 

thanks,


----------



## SilverFox (Apr 1, 2006)

Update:

Cy's data has been added to the graph and table in the first post.

Tom


----------



## Leef (Apr 3, 2006)

I've just gotten into this measurement game. As I read thru this long thread, I see that there's LOTS more here than I originally assumed. That's not surprising, but it does cause me to go back to the beginning and make sure I know why I'm doing this, lest I end up spending way too much time for not much benefit.

I'm interested in very few simple-sounding questions: 1) how "bright" is this light compared to all the others? 2) What does the brightness do over time as the batteries run down; which kinds of batteries suit my needs best (primary, rechargeable)? 3) What's the throw and the spill of various lights? 4) What's the color? I expect there are some others I haven't thought of.

I seldom wake up at night worried about what numbers would come from measurements of my (current and future) lights. What I do care about is how well a flashlight will help me see in different conditions of darkness (e.g. black nights, in shadowed areas in sunlight, etc).

Still, I'd like to know that my dearly beloved Photonator Eleventyteen puts out X lux, and throws Y (units?). And I'd like to know these numbers in terms that we all share so I can evaluate a prospective purchase.

I'll keep reading, and fooling around with my Extech datalogging meter, my light box, and my lights. I hope I'll discover that this endeavor is practical.

My hat's off to you all for the serious work. Any comments very much appreciated.


----------



## cy (Apr 4, 2006)

Leef, the Ubin in X1 tint to me was yellow/greenish tint. others may see differently. brightness is harder to describe, but was close to several of my lights. due to request not to burn lights excessively. only time brightness was compared was during warmup phase of test light. 

but note percived brightness is based partially upon eye's sensitivity to different wave lengths. 

Please note you cannot take lux reading and transpose that number to lumens. you would only be able to get close if one uses the exact same relector at exact same focus. 

for an example a mini-pro which is one of my brightest Tbins. put out lumens almost identical to test Ubin. but lux readings was aprox. 1/2 of test Ubin.


----------



## wquiles (Apr 4, 2006)

cy said:


> Leef, the Ubin in X1 tint to me was yellow/greenish tint. others may see differently. brightness is harder to describe, but was close to several of my lights. due to request not to burn lights excessively. only time brightness was compared was during warmup phase of test light.
> 
> but note percived brightness is based partially upon eye's sensitivity to different wave lengths.
> 
> ...


Well said cy. I am really hoping I will some day be able to get a hold of a "calibrated" or known Lumen LED so that I can calibrate my Light Box project. For now I can make accurate and repeatable measurements, but I have no idea of how these measurements are related to actual lumens 

Will


----------



## cy (Apr 4, 2006)

Will, I have an ARC4X that's been measured at 48.3 lumens. that light is used for a referance point many a time.


----------



## wquiles (Apr 4, 2006)

cy said:


> Will, I have an ARC4X that's been measured at 48.3 lumens. that light is used for a referance point many a time.


Thanks cy. PM sent 

Will


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## Archangel (Apr 6, 2006)

woo-hoo! Got 'em today.


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## sygyzy (Apr 7, 2006)

Is there going to be some sort of summary or results thread? It'd be nice for those of us looking to buy light meters to get some sort of quick top 5 list or best bang for your buck recommendations.


----------



## SilverFox (Apr 7, 2006)

Hello Sygyzy,

The best summary so far is the charts in the first post of this thread.

When this first round of testing is completed, I am planning to send the lights to a laboratory to have them "officially" tested. From that, we should have a better idea of where our light meters stand.

Tom


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## Archangel (Apr 9, 2006)

Here's my numbers. Now i can see why people spend the big bucks for the meters that keep the peak reading, because i was able to watch the numbers drop in the time it took me to find the max reading. I also kept the torch on between the three readings (i wasn't positive we were supposed to), which didn't help matters as far as the battery is concerned. The thermometer read 71F, though it felt warmer.

A2 - 2130, 2100, 2100 /2110/ (all were on the x10 scale)
blue - 386, 384, 382 /384/
green - 1777, 1770, 1765 /1770/
red - 1890, 1870, 1860 /1873/

My light meter is from Harbor Freight. Model #91194.


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## Leef (Apr 9, 2006)

Does anyone have any experience or comments about the accuracy of the Extech 401036 datalogging meter? Cost ~$280.


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## SilverFox (Apr 10, 2006)

Hello Archangel,

I believe there is also a white LED. Do you happen to have your results from testing that light?

Tom


----------



## Archangel (Apr 10, 2006)

Oops. 960, 950, 940 /950/


SilverFox said:


> I believe there is also a white LED. Do you happen to have your results from testing that light?


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## SilverFox (Apr 10, 2006)

Hello Archangel,

Thanks.

The graph and table in the first post have been updated with your test results.

Tom


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## Archangel (Apr 10, 2006)

BTW, they were sent on their way this afternoon.


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## Brock (Apr 16, 2006)

Picked them up at the post office yesterday.


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## Brock (Apr 18, 2006)

I am going to post them here so I don't loose them 

A2 - 2000
White - 1200
Blue - 190
Green - 1850
Red - 1300

I should get them out to Codeman tomorrow


----------



## SilverFox (Apr 19, 2006)

Hello Brock,

Thanks.

We are also keeping track of meter manufacturer, serial number, and the temperature when you were running the tests. 

While we may be able to make an educated guess as to the meter used, based on the blue and red LED response, I would rather you just tell us what it is...  

Tom


----------



## Brock (Apr 19, 2006)

Yes, I will get it to you, I just wanted to write the results in a place I couldn't loose them


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## N162E (Apr 21, 2006)

Leef said:


> Does anyone have any experience or comments about the accuracy of the Extech 401036 datalogging meter? Cost ~$280.


Hi Leef I have that meter and like it a lot. My results are in post 301 of this thread. From the testing so far I think my results are fairing well. The peak hold and seperate wired photocell are very useful. The logging and graphing program are awkward and a little archiac but do the job. I'd shop that price, from what I can find the going rate is more like $229.00 at http://www.ambientweather.com/ex40limedawi.html and the nist certified version about 80 bucks more. Mine is the standard one.


----------



## NewBie (Apr 22, 2006)

*Re: Light Meter Benchmark Testing – CPF style*

Other meters that are available from Extech:
http://www.extech.com/instrument/categories/light/light.html

The 407026 has a feature so you can select different light sources to enhance accuracy by selecting lighting type Tungsten/Daylight, Fluorescent, Sodium, Mercury) 

Allied Electronics has this one for 184.00:
http://www.alliedelec.com/Search/SearchResults.asp?SearchQuery=407026

Mouser has them for 169.00:
http://www.mouser.com/index.cfm?&ha...26&Ntt=*407026*&Ns=SField&N=68500000&crc=true

You can check out the Extech software here:
http://www.exstik.com/instrument/softwareDownload.html

Standard light meters are not that accurate for lux, when the spectrum shape departs from the exact spectrum it was calibrated with. The meters with the correction factors help out this problem alot.

One of the biggest problems of the 401036 is that it has no settings for different spectrum light sources.


If you take a look at this datasheet:
http://catalog.osram-os.com/media/_en/Graphics/00029567_0.pdf

This is a much higher end photodiode than is found in a typical light meter. Go to page 4, and look at the top left, the chart labeled Relative Spectral Sensitivity. The narrow curve with the V label and dashed line, is the actual spectral response of the human eye. The solid line is the response of the sensor. 

If one was measuring a white LED, the high amount of 470nm blue emission in the white LED would cause a higher reading in the blue portion of the spectrum, by a factor of 700% higher than the sensitivity of the human eye. The much greater response on the red end, would cause an incandescent light to read much higher due to its very high output red end of the spectrum. This adds a huge error into things. Without the spectral correction settings (or the math for it in the manual), you can easily induce a 20% error or more. Some meters say they are spectrally corrected and don't need the settings, but the spectral correction is the filter that is placed over the photodiode. The one I linked, the BPW21, has a built in matched filter, and it is pretty easy to see how much error could creep in on things. It would be cool to see light meters add a white LED correction factor, or give you the math, like Lux-(Lux*20%) or whatever. Unfortunately, they can't correct for the spectral variations from LED to LED.


----------



## N162E (Apr 23, 2006)

NewBie said:


> Other meters that are available from Extech:
> http://www.extech.com/instrument/categories/light/light.html
> 
> The 407026 has a feature so you can select different light sources to enhance accuracy by selecting lighting type Tungsten/Daylight, Fluorescent, Sodium, Mercury)
> ...



Good info here Newbie. I was not aware that other meters that people were using in this group measured selectable sources. I will be curious to see how our meters stack up against your 25K spectroradiometer.


----------



## Codeman (Apr 25, 2006)

I've got the lights and plan to do the measurements tomorrow.


----------



## SilverFox (May 3, 2006)

Update:

I am still waiting on meter model and serial number from Brock.

Codeman will be posting his results in the near future.

The lights are being sent to Lighting Sciences Inc. to be included in Peter Gransee's tests after which they will be certified by LSI. We were going to do this at the end of the pass around, but decided to take advantage of this opportunity.

After LSI, they will go to NextLight and we will continue on with the pass around.

There is some cost involved in getting the lights certified and if you would like to help out with the costs check out this thread.

Certified lights will give us answers to the question of "How close are we in our measurements?" We should have the results sometime next week. There have been some suggestions that the official results should not be published until the end of the pass around... any comments?

Tom


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## evan9162 (May 3, 2006)

I think it's a good idea to wait until the end before publishing "official" results. This will reduce the chance of introducing bias into the remaining measurements, by making sure no one (even subconciuslly) tries to get their meter to get the "right" reading.


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## Codeman (May 3, 2006)

SilverFox said:


> ...There have been some suggestions that the official results should not be published until the end of the pass around... any comments?



I'll get my results to you this evening. I thought I'd already posted them. Darned old age strikes again...

I too, think the official results should be posted after the pass around. A big discussion will follow that posting, so the thread will be "cleaner" this way. 

As to whether knowledge of those results might skew the results for those testing afterwards, it would possibly "pollute" the blind nature of the testing completed prior to the official results being posted, so we'd have 2 groups of testing -blind and not blind. I don't think that's good from a group perspective. But they could be useful to know for the individual. If someone's measurements are off, that might be an indicator of where their technique could be improved.

I know if my readings are off by much, it would be nice to get the lights for another test to see if improving my technique might yield results closer to the official ones. If not, then I'd assume I'm either inept, or my meter isn't very accurate.


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## bwaites (May 3, 2006)

I would like to see the real readings, but I understand the need to avoid bias in those still testing.

Is there a way to set up a site where you can see it by password only, and then Silverfox could give the password to those who have posted? 

The deviation in the RED, GREEN, BLUE portion is staggering! The white and Incan sections are reasonable.

Bill


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## Codeman (May 3, 2006)

Most of the meters are built using a single light source (CIE standards) so that the meters are accurate for ambient lighting - an attempt to measure what the human eye perceives. The spread may actually be quasi-proof that LED light is indeed perceived differently by the eye from sunlight and incandescent sources.

I'd bet a box of Krispy Kremes that the more expensive meters would be more consistent with separated colors. I seriously doubt our <$200 meters use separate sensors to break light down into primary colors for measuring. What may seem like wild swings may simply be misleading exaggerations of small variances in the sensors that simply don't impact the intended use of these meters - ambient lighting. After all, these meters weren't designed to measure "colored" light.


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## HarryN (May 3, 2006)

I guess there are different ways to look at it. It is really no longer a blind test anyway, because people later on the list can easily see the results of others, and it is entirely natural to assume that the average is closer to the truth than some other measurement, at least for white.

I would like to see the data as soon as possible. I can report the data using my "standard" technique" and then see if my technique needs improvement - something which I can do real time the same evening. That is a different aspect of the testing, and one of the main points of the exercise - to help us improve our light measurement quality.


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## McGizmo (May 3, 2006)

I too would like to see the data points posted as soon as possible. This isn't a contest. If folks are inclined to fudge their numbers then they will do so and only they know why they are so inclined. :shrug: I hope I have been consistant in my efforts to measure the light and if I have been then knowing what the true measures are will give me an idea of how I should adjust my readings to closer approach the absolute.


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## Codeman (May 4, 2006)

My results:

Ideal-Sperry Model 61-681 S/N 030286 (re-branded LM631)
Temp - 69°F

A2Incan - 2390, 2410, 2420 - avg 2407
White - 1206, 1218, 1178 - avg 1201
Blue - 254, 249, 251 - avg 251
Green - 2690, 2680, 2690 - avg 2687
Red - 1178, 1174, 1175 - avg 1176


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## SilverFox (May 4, 2006)

Update:

I have added Brock's data (I think he is using a Meterman...) as well as Ray's.

Ray has sent the lights to Peter Gransee who will be taking them to LSI tomorrow. I checked with Peter and he has the lights in hand.

Thank you Ray for going out of your way to get these lights FedExed to Peter and for donating the cost of shipping.

Thank you NextLight for patiently waiting for your turn while the lights are being tested.

Peters testing will be very interesting, and the certification of our benchmarking lights hopefully will answer some questions that we have about our light meters.

Tom


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## yaesumofo (May 8, 2006)

I don't know how to feel. I see my name moving closer to the top so to speak. I am looking forward to the challange. I am redesigning my test setup for this test. 

Cool.
Yaesumofo


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## SilverFox (May 10, 2006)

Update:

I talked with Peter today and he told me that he was in the middle of testing the benchmarking lights. His testing should be finished today and then he will hand the lights off to LSI for the official certification.

We still have some expenses to cover for this testing. If anyone is feeling generous, PM me for my PayPal address. Your contribution will be greatly appreciated.

Tom


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## SilverFox (May 12, 2006)

Update:

LSI has our lights and we should have the test results by the end of next week.

That leaves on week for you to send in your generous contributions...  

Tom


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## Bullzeyebill (May 14, 2006)

Tom, what amount are people putting in toward the LSI lumen tests?

Bill


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## SilverFox (May 14, 2006)

Hello Bill,

We have had a "less than stellar" response in covering the expense of getting these lights tested. The details are in this thread. I believe we have had contributions from 10 people.

It seems that a lot of people are interested in how their light meters compare to others, but very few are interested in what the actual calibrated response should be.

There is no minimum amount set and the maximum is the actual cost of the certification testing.

Tom


[Sarcastic Mode On ]

I have invested a lot of time, effort, and money in various testing and have freely shared that information on CPF. The paltry response to get some of the expenses covered on this project makes me think that I need to begin charging people a fee to check out their light meters... Perhaps I should also be charging for battery test results...

[Sarcastic Mode Off ]


----------



## wquiles (May 14, 2006)

Tom,

As one of those "few" who donated money to cover these expenses, I wonder what is going on. I would had "expected" that at the very least, everyone involved in this Light Meter Benchmark would have donated something: $10, $20, minimum - we certainly spend way more than this on "stuff". I just don't get it  

Will


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## Bullzeyebill (May 15, 2006)

I'm in.

Bill


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## SilverFox (May 16, 2006)

Update:

I talked with LSI and believe the lights will be tested today.

Tom


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## Bullzeyebill (May 16, 2006)

I'm looking forward to this. I bet A2 comes in at about 72 lumens.

Bill


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## SilverFox (May 17, 2006)

Update:

People have contributed enough to offset the costs of the lux testing. Don and I are going ahead with the lumen and spectral testing, but the results of that testing will be handled a bid differently.

Don and I would like to thank everyone for their generous contributions. We feel that there is some very valuable information here, and it seems that this view is shared by a few of you as well. Thanks.

I will post the results of the lux testing in the first post of this thread.

LSI will be providing us with lumens, spectral plots, x y coordinates, CRI and CCT values, as well as a spreadsheet with the spectral values per nanometer. We will make this information available to those who have contributed. If anyone else is interested in this information, it will be available for a $10 contribution to the testing costs. PM me for my PayPal address.

The testing is scheduled for today. The results should follow, shortly.

Tom


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## SilverFox (May 19, 2006)

Update:

I was in touch with LSI today. They performed the illuminance measurements, but are not satisfied with the results they got. They will be doing the lumen and spectral testing next week. From the spectral tests, they will adjust the illuminance values to compensate for the sensitivity response of their light meter. Once this adjustment is made, we will have the true values.

There may be some interest in their "raw" data, so here it is in foot candles at 1 meter:

A2 incandescent 233
White LED 120
Blue LED 16
Green LED 235
Red LED 180

Tom


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## Bullzeyebill (May 19, 2006)

Thanks boss, just following your instructions. LOL.

Wow, look at the green luxeon. Blue is strange. If that is close to true then our LM631's really have problems with blue measurements.

Bill


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## tvodrd (May 19, 2006)

Tom,

I have to pleed just too much going on, and have to remove myself from the pass-around to sorta calibrate my LM631!  

"I have invested a lot of time, effort, and money in various testing and have freely shared that information on CPF. The paltry response to get some of the expenses covered on this project makes me think that I need to begin charging people a fee to check out their light meters... Perhaps I should also be charging for battery test results..."

Can I send it to you? :green: 

Just jokin' guys and thank you for the effort to add some _science_ to our hobby!!!!! Please don't get discouraged by the wannabe fen!!!

Thanks, Tom for the science you are providiing to the _real_ knowledge base here!!!!

Larry





SilverFox said:


> Hello Bill,
> 
> We have had a "less than stellar" response in covering the expense of getting these lights tested. The details are in this thread. I believe we have had contributions from 10 people.
> 
> ...


----------



## SilverFox (May 20, 2006)

Update:

I forgot to point out that the LSI raw data is in foot candles at 1 meter. To convert to lux at 1 meter, you have to take their data and multiply it by 10.764.

We believe that the data from the A2 incandescent is correct. The LED data may be subject to correction. I was thinking that the white LED data would be close, but they want to look at the spectral data before agreeing to that.

Tom


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## Codeman (May 20, 2006)

A difference of just 4% for my A2 testing (2407 vs LSI's 2508) is encouraging! That's certainly closer than I expected.

Given how our combined average of 2354 is only 6% low, It looks like we're doing a pretty good job with our techniques, overall.

Can't wait to see the corrected LED values.


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## csheehy (Jun 2, 2006)

Post deleted by csheehy-reposted in different (correct) thread.


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## Codeman (Jun 2, 2006)

Have we heard back yet from the testing, Tom?


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## SilverFox (Jun 2, 2006)

Hello Ray,

It seems that the end of the month brought several "emergency" jobs to the front. We were pushed back. They are setting up for the tests today and should run the tests on Monday.

Tom


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## Bullzeyebill (Jun 6, 2006)

Hi Tom, any updates from yesterday's LSI tests?

Bill


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## SilverFox (Jun 7, 2006)

Hello Bill,

I will be calling them tomorrow to find out what they came up with.

Tom


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## SilverFox (Jun 7, 2006)

Update:

Since we have ordered color spectrum along with lumen and lux test results, LSI started testing our lights in their 2 meter sphere. The calibration lamp for their color system is quite large and they use it with the larger sphere.

A problem came up in that some of our lights do not put out enough light to get a good color signal for analysis. They have moved to the 1 meter sphere for lumen testing and are setting up the color testing outside of a sphere. This can be a bit tricky because they have to adjust the lumen numbers for the visible spectrum. If you are collecting color and lumen information from the same set up, it is a lot easier.

After two days of testing, they are making progress but we still don't have final results.

Pass the popcorn and stay tuned...  

Tom


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## wquiles (Jun 7, 2006)

Will


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## Codeman (Jun 7, 2006)

Thanks for the update, Tom!


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## Bullzeyebill (Jun 7, 2006)

Yes, thanks Tom. The testing procedure must be very complicated, and certainly time consusming. Far cry from my simple lux testing and "IS bathroom". LOL.

Bill


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## schiesz (Jun 9, 2006)




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## SilverFox (Jun 15, 2006)

Update:

We have "official" numbers now...

Lux at 1 meter
A2 Incandescent - 2508
White LED - 1270
Blue LED - 151
Green LED - 2357
Red LED - 2379

I will be updating the graphs in the first post shortly.

Tom


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## wquiles (Jun 15, 2006)

Excellent - thanks much Tom 

It looks neither one of my meters is "right" although a combination of the two meters that I used would have been "OK" :nana: 

For incandecents and white LEDs, looks like my Luxtron is a better choice 

Test #1 - Meterman LM631 Light Meter, Serial 0503014
Recorded on 3/21. Temperature 61F
Light=Measurement ([email protected]) #1/#2/#3=Average
A2=2200/2260/2230=Ave=2230 (12% low)
A1 White LED=836/850/854=Ave=847 (50% low)
A1 Blue LED=823/817/820=Ave=820 (82% high)
A1 Green LED=1279/1298/1286=Ave=1288 (83% low)
A1 Red LED=2370/2340/2420=Ave=2377 (0.08% low - right on the money !!!)

Test #2 - Lutron LX-102, Serial Q030770
Recorded on 3/23. Temperature 53F
Light=Measurement ([email protected]) #1/#2/#3=Average
A2=2520/2540/2490=Ave=2517 (0.35% low - right on the money !!!)
A1 White LED=1211/1147/1193=Ave=1184 (7.3% low)
A1 Blue LED=760/750/750=Ave=753 (80% high)
A1 Green LED=2670/2650/2670=Ave=2663 (11.5% high)
A1 Red LED=1580/1600/1570=Ave=1583 (50% low)


Will


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## evan9162 (Jun 15, 2006)

My meter results are right in there with wquiles:


```
Lab	Mine	Correction Factor
A2	2508	2265	1.11
White	1270	869	1.46
Blue	151	920	0.16
Green	2357	1341	1.76
Red	2379	2420	0.98
```

Now to update everything


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## NewBie (Jun 17, 2006)

*Re: Light Meter Benchmark Testing – CPF style*

Interesting results, some of the meters look to be an easy 30% off (Meterman LM631).

White LED:
847/1270= 0.667
1 - 0.667 = 0.333
0.333= 33.3%

For some of the color LEDs, the numbers are way off.

Would be interesting to have done this with a few different while LED color bins....


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## McGizmo (Jun 17, 2006)

Tom,
Thanks for ridding herd on this project and all of your time and out of pocket money!! I think the results points to considering that any posted lux measures have relative value if compared to readings of other lights from the same meter but in absolute terms, YOUR MILEAGE MAY VARY.

On one hand, we have a certified lab that takes a couple extra weeks to get their measurements _right_ and on the other, we have talented CPF members who can pull lumen values right off the wall! :nana:

BTW, It looks like our Extech EZ views are not only easy on the eye but easy on the believability factor as well.


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## Bullzeyebill (Jun 17, 2006)

Jeez Don, I take my lumen readings off the "ceiling", not off the "wall".

Bill


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## SilverFox (Jun 17, 2006)

Update:

I have sent the complete test results to all who helped with the cost of getting these lights tested.

Tom


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## jugeh (Jun 17, 2006)

Thanks to all CPF'lers hard working on this project.

I'm a quite new to CPF and this is my first post.
I calculated the deviation of the values to the values of the LSI reference. So here are some of my personal conclusions based on the data presented:







1. Forget about the color LED values. The deviations are so big because of bad adoption of the light meters to the human's eye curve. 
2. Even light meters of the same type behave very different.
3. If you sort the Metermans by serial# you will find that they changed something in the production (I guess in April 2004), so the newer are worse for white LED but quite constantly -30% off. Maybe they are now optimized for red LED?
4. One of the cheapest (Cen-Tech FX-101) seems to be the best but this can also be an outlier.
5. Most light meters have an accuracy of >+/-5%. So 10% difference between two units is still normal.
6. There should have been more units participating to proof the results.

Finally I still don't know witch light meter I will buy.

Jürgen


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## Codeman (Jun 17, 2006)

A big ditto on McGizmo's thanks! :bow:

Thanks for the std dev chart, Jürgen! Most of these meters, in particular the Meterman and Sperry, are intentionally calibrated to measure "daylight", not specific-spectrum light sources as seen by the human eye. We're really using these meters for a purpose they aren't designed for.

While so-called "white" lights can be measured reasonably well (IMO, 10% or less error), using them on colored light sources is really outside of the meters intended use. Even so, the data is still useful when comparing different, say blue, lights with the same meter, or the same light with multiple meters.


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## HarryN (Jun 17, 2006)

I think you will find the curves and statistics more useful if you assume some muli modality instead of assuming a gaussian distribution.


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## NewBie (Jun 17, 2006)

*Re: Light Meter Benchmark Testing – CPF style*



Codeman said:


> A big ditto on McGizmo's thanks! :bow:
> 
> While so-called "white" lights can be measured reasonably well (IMO, 10% or less error), using them on colored light sources is really outside of the meters intended use. Even so, the data is still useful when comparing different, say blue, lights with the same meter, or the same light with multiple meters.



How do you figure 10% error, when there is clearly a 30% error for alot of the Meterman LM631s and White LEDs? Are you referring to Incandescents only?

As far as the date of manufacture, it looks like the two oldest Meterman LM631 units have a 20% error.

The Harbor Freight unit looks to be as good as the Meterman LM631.

The ExTech units look to be pretty close for both white LEDs and Incandescents.

All the units look pretty poor when dealing with colored LEDs. I still think it would be quite interesting to see what happens with various white bins of LEDs...especially after seeing massive errors for the color LED numbers...


----------



## Codeman (Jun 17, 2006)

NewBie said:


> How do you figure 10% error, when there is clearly a 30% error for alot of the Meterman LM631s and White LEDs? Are you referring to Incandescents only?
> 
> As far as the date of manufacture, it looks like the two oldest Meterman LM631 units have a 20% error.
> 
> ...



I didn't - you mis-understood my post. Try replacing the word "can" with the meaning of the word "can" that I intended - "have the potential to".

Also, note that in the phrase "reasonably well (IMO, 10% or less error)", "10% or less error" is my opinion of what constitutes "reasonably well".


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## lildave (Jun 19, 2006)

Tom, got the lights today will test tonight and ship asap.


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## lildave (Jun 20, 2006)

ok here it goes got the lights today.

A2 2320, 2280, 2260
a1 uxij 978, 963, 965 (a little green for my taste)
k2 red 2850, 2870, 2800
blu 996, 994, 983
green III 1561, 1565, 1559

meterman lm631 (from the GB) 0503030

The funny thing is I grabed a red pen to write the results, when I came to write the red results I thought my kids took my page cause the page I had was blank it was the same color as the ink so I had to go to the next room to see my writing.

I will be shipping soon I have yaesumofo's address.


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## yaesumofo (Jun 24, 2006)

I have received the lights for testing today.

I was wondering if it would be OK to replace the packaging with a heavy duty Pelican case size appropriate. I have a great source for these and they are lockable/seal able so tampering is evident. Colored zip ties perform this function. I Use these cases to ship expensive (I mean really expensive. This particular case is use to ship my 744T 4 track motion picture sound recorder in. Well it was expensive to me anyway) sound equipment World Wide with these cases and they perform flawlessly. They would add a Bit of weight to the shipping expense but the amount of security added is well worth it in my opinion. I will be happy to make this contribution to the cause since these lights still have a great deal of traveling to do.
What do you say?










This is just a mock up but I would be happy to contribute this. These cases are easily shipped using any form of shipping postal included.

Say the word and I will make it happen.

I will have my measurement data done in a day or 2 or three and I will then ship these very cool pieces off to whom ever is next.
Please instruct me via PM or here as to weather or not to use the hard case.
Yaesumofo


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## SilverFox (Jun 24, 2006)

Hello Yaesumofo,

That is an excellent idea.

The only down side I can think of is that it may cost more for shipping. 

The packing of these lights has been an interesting evolution. Don shipped them to me taped to the side of a box. I wrapped them in bubble packing, then someone cut out a foam block for them. Now we are considering a real case.

I believe the lights are tough enough to withstand the mail service, however now that they have been certified a case makes sense.

Could you check to see how much it would cost to mail the lights in the case?

Tom


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## yaesumofo (Jun 24, 2006)

Shipping weight with the lights would be 5 Lbs. so shipping would cost what ever the postal service charges to ship 5 Lbs.
The rate depends on where the package is going. I used the postal rate calculator and checked from my zip to a zip somewhere like in Maine, basically the furthest place I could find and the first class rate with delivery confirmation is $10.54.
for me to ship it to san francisco with delivery confirmation it would cost $7.91
ups ground charges $7.59 for the package from Los Angles to san francisco.

I think the lights should go into a case. They will be treated a whole lot better than the beat up box of peanuts I received.
Let me know Tom. basically the weight will go from 2 LBS to 5 Lbs. Is it worth the extra protection? These are delicate instruments which are the protected standard of the CPF community.

If you make a decision now in the next couple of hours I will go get the case this afternoon.

BTW the case I am looking at is the Pelican 1400.
There is a smaller version, the 1200 which would weigh no more than 3.5 LBS packed.
It is not nearly a substantial as the 1400.
I would be willing to go either way. 
There is a pelican store that stocks EVERY pelican product I would most likely go there with the lights in their foam and get the case that they recommend for the lights. These new Pelican cases come in a variety of colors. I like the tan but maybe the bright orange would be a better choice. go to 
http://www.pelican-case.com/1200.html
and have a look and let me know what you think ASAP if possible.
Yaesumofo




SilverFox said:


> Hello Yaesumofo,
> 
> That is an excellent idea.
> 
> ...


----------



## SilverFox (Jun 24, 2006)

Hello Yaesumofo,

I think it is a good idea. Let's go with the smaller case and it will not impact things much at all, and they will be well protected.

Since there have been no objections, I say go with it.

Tom


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## wquiles (Jun 24, 2006)

I concur with Tom. The smaller case should be a great compromise 

Will


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## evan9162 (Jun 24, 2006)

Now we can carry around the CPF reference lights in a hard case, like we we're from NIST; carrying around the inch, centimeter, ounce, pound, and kilogram, on our way to an important measuring meeting.

Or something like that.


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## Codeman (Jun 25, 2006)

Don't forget that insurance costs need to be added as well.

I'd go with the 1200 as well, but in black, tan, or any subdued color. IMO, orange could attract un-necessary attention during transit. No sense in putting a target on 'em, especially if someone forgets the insurance and the case ends up sitting on someone's doorstep...

To me, orange says that whats inside is worth enough that the owner wants to be able to spot it, so it's a signal to would be thieves that the contents may be more worth stealing.


----------



## SilverFox (Jun 25, 2006)

Update:

I have added the data from LSI and Lildave to the graph in the first post.

Tom


----------



## yaesumofo (Jul 3, 2006)

Here are my numbers:\\\\


CPF A2 2086
red 1210
white 1080
blue 186
green 2333

these are all @ 1 meter 


The meter is a meterman LM 631 SERIAL NUMBER 0301139
I Put the lights into a NEW TAN pelican 1200 case. the instructions are in the lid and their are some more zip ties under the foam.

The lights are off to Tvodrd next.

I must have a weak A2 because on fresh cells it only puts out 1550 lux. Strange.
Yaesumofo


----------



## Codeman (Jul 3, 2006)

It's nice to see the lights getting back into the population.

A big thanks, yaesumofo, for the new case!



yaesumofo said:


> ...
> I must have a weak A2 because on fresh cells it only puts out 1550 lux. Strange.
> Yaesumofo


Maybe it's just time for a new bulb?


----------



## HarryN (Jul 3, 2006)

Yaesumofo - I tried to reply to your PM but your box is full.

I will be traveling for about 1.5 - 2 weeks. Please contact gadget lover as the next user. I will pick it up at his house.

Thanks


----------



## Codeman (Jul 3, 2006)

<Needless question removed>

Thanks for showing the LSI data as lines, Tom!


----------



## Bullzeyebill (Jul 3, 2006)

HarryN, Tvodrd needs to get that message. Right?

Bill


----------



## HarryN (Jul 3, 2006)

Bill - Yes - the line should actually be TVROD then Gadget Lover then me IIRC.


----------



## yaesumofo (Jul 3, 2006)

Tvodrd is out of it. I will contact Gadget Lover.

HarryN can attempt to get back in the loop later.
Yaesumofo



Bullzeyebill said:


> HarryN, Tvodrd needs to get that message. Right?
> 
> Bill


----------



## SilverFox (Jul 3, 2006)

Update:

I have updated the graphs in the first post to reflect Yaesumofo's results.

Thanks Yaesomofo for the case. This will dress things up a lot.

Tom


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## gadget_lover (Jul 8, 2006)

The box got here yesterday, in great shape. I've not had a chance to start playing. Maybe this evening?

Daniel


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## yaesumofo (Jul 15, 2006)

I am happy to hear the case made it in one piece. I have found the pelican cases to be incredibly durable. Able to withstand the most abusive cargo carriers. I have sent equipment all over the world in these cases and have always had the equipment and the case survive.
Cases of that size are difficult to remove (steal) from the system because of their bulk. 
FED EX usually attaches a plastic bib like thing for paperwork attachment. If anybody comes across one of those it would be great to add to the case. There is not that much room for stickers and bar-codes and stuff like that on this small case.
It was my pleasure to provide the case. This project is worth it. These are OUR GOLD Standards. They deserve a good home. Now they have one. 

Yaesumofo





gadget_lover said:


> The box got here yesterday, in great shape. I've not had a chance to start playing. Maybe this evening?
> 
> Daniel


----------



## Bullzeyebill (Jul 22, 2006)

Daniel, are you there?

Bill


----------



## HarryN (Jul 28, 2006)

I spoke to Daniel a few days ago - working a lot of hours. We are coordinating to get our tests done more or less together.


----------



## TinderBox (UK) (Aug 5, 2006)

I just bought an DMM with an light meter built in.

mine reads -0025 on the display with the light sensor covered up.

should it not be 0000.

The meter has a relative button that zeros the display.

I have calibration instructions that I received when I bought it, but as I don't have an calibrated light source to set it.

anybody have an suggestions.

thankyou.


----------



## yaesumofo (Aug 5, 2006)

If you can't do the test in a timely manner pass the lights to the next in line. 
IMHO holding on to the test package for more than a week is doing a disservice to this test and this group. The entire testing process shouldn't take more than 1 hour. That is ONE hour MAX.
No one set of data is worth a three wek wait.
To take a month or even 3 weeks is not cool in my opinion. Just pass if you can't do it or if it is going to take so long.
Sorry to rant about this but the data collection process is taking long enough without people holding on to the test for weeks at a time.
do the test or pass it on.
Yaesumofo





HarryN said:


> I spoke to Daniel a few days ago - working a lot of hours. We are coordinating to get our tests done more or less together.


----------



## yaesumofo (Aug 5, 2006)

I would check with your local professional photo shop. Pro photographers send their meters in for calibration on a regular basis. Maybe you should do the same.
Yaesumofo



TinderBox (UK) said:


> I just bought an DMM with an light meter built in.
> 
> mine reads -0025 on the display with the light sensor covered up.
> 
> ...


----------



## TinderBox (UK) (Aug 6, 2006)

right 490 post in this thread.

so their must be a list of lux measurement's for various flashlights at 1 meter.

can sombody post a link to it.

thanks.


----------



## Codeman (Aug 18, 2006)

What happened to the testing?


----------



## SilverFox (Aug 18, 2006)

Hello Ray,

It appears that Daniel has been swamped with work. I have asked him to pass the lights on to the next person beyond HarryN. Harry is going to be gone for a while and won't have time to test either.

Hopefully Daniel will get my PM and pass the lights on. I believe Harry also sent him an email.

Tom


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## yaesumofo (Aug 23, 2006)

So I see the testing has stalled out. WTF? He has had the lights over a month. send them on.
Lets get this test done.
Yaesumofo


----------



## gadget_lover (Aug 23, 2006)

Yes I've been swamped. I just talked with Harry, and he confirmed that he will need to pass. 

The kit goes to Bullzeyebill next, according to the first post. (PM sent)

My appologies for holding onto the lights so long. I measure time badly, and have had only 3 days off since the pack arrived, so time's been a blur. I could have sworn they were here only two weeks.

I'm including an 8-pack of CR123As by way of appologies to the rest of the people who've been waiting. 

I did my readings late one night in a dark garage. A stick was marked at 29.5 inches from the sensor. The meter is an off-brand labeled only MS6610. The meter was on the 10x setting, so all readings are accurate to +- 10.


LIGHT 1 2 3
a2 2540 2610 2690
red 2090 2040 1990
green 1990 2050 2030
blue 2060 2110 2090
white 1360 1330 1330


Daniel


----------



## SilverFox (Aug 23, 2006)

Hello Daniel,

Good to hear that you finally got a few days off. 

Keep in mind that all work and no play... Sucks, but it does pay the bills.

Are you sure about the measurement? 29.5" seems a little short for 1 meter...

I will get your data on the graph and update it shortly.

Tom


----------



## Bullzeyebill (Aug 24, 2006)

That would be 39.5 inches, and no doubt a typo.

Bill


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## Bullzeyebill (Aug 25, 2006)

Got the package from gadget_lover. Haven't opened it yet. Will start testing tomorrow nite. Big box.

Bill


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## gadget_lover (Aug 26, 2006)

The box is big because my wife is VERY thorough. Lots of packing. I didnt have the heart to explain to her that the pelican box does a great job of protecting the lights all by itself.

Yes, the 29.5 was a typo. It was 39.5 inches in a yard. 

Yes Tom, too much work does pay the bills. We have just caught up from my not being able to work last year. Yea! Maybe I can slow down soon and particpate on CPF again (hope-hope-hope).

Daniel


----------



## SilverFox (Aug 26, 2006)

Hello Daniel,

I have updated the graphs and charts on the first post to reflect your test data. Thanks.

Tom


----------



## PEU (Aug 27, 2006)

it seems I may get the test box by the end of this year from what I see in the list, cool, a lm631 is waiting here 


Pablo


----------



## Billson (Aug 28, 2006)

gadget_lover said:


> Yes, the 29.5 was a typo. It was 39.5 inches in a yard.


Hello Daniel,

Another typo. 39 inches to a meter. 36 inches to a yard.


----------



## Bullzeyebill (Aug 28, 2006)

Here are my numbers:

A2: 2370, 2380, 2361 Average 2370 Surefire CR123's

Aleph 1: Streamlight CR123's

White: 1130, 1128. 1132 Average 1130
Red: 820, 824, 818 Average 821
Blue: 280, 288, 282 Average 283
Green 2570, 2565, 2573 Average 2573

Room temperature was 70 degrees
Tripod was used for testing all lights against a light tan wall.
Aleph tailcap was attached to camera mount on tripod
Sure A2 was held with rubber band to tripod camera platform. 

Meterman LM 631 #0307411
Peak and hold functions were not used
All batteries were fresh. Run minimum of two minutes prior to testing.

I was surprised by low reading with red led. I repeated this test several times with similiar results to three runs posted. I had started out with one of gadget lovers supplied Batterystation with Aleph 1 and switched to a fresh Surfire after seeing results of red led, and redid the white Aleph 1. Surefire's made no differences with led led.

All of my reading were lower than LSI results. There were fresh batteries in my LM631.

Bill


----------



## SilverFox (Aug 28, 2006)

Hello Bill,

I have updated the graph and chart in the first post with your numbers. Thanks.

Tom


----------



## Bullzeyebill (Aug 28, 2006)

I contacted croMaglite, next in line, and he is passing on tests, so I sent a PM to Robstarr-Lite. 

Bill


----------



## Bullzeyebill (Sep 2, 2006)

To bring all up to date on status of benchmark lights, when Robstar-Lite did not respond to my PM and I noticed that he had not posted in CPF for a month, I contacted next in line, modamag. Modamag was on vacation and asked me to send lights out Friday (today), which I did. Robstar-Lite just PM'd me and asked if he could stand out of line for awhile due to some pressing home issues. Tom, would you contact him toward end of passaround, and see if he is ready?

Bill


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## SilverFox (Sep 7, 2006)

Hello Bill,

I will adjust the list.

Tom


----------



## Reima (Sep 9, 2006)

Hi Tom,

Is it too late to get on the list?
I recently got my light meter.
RC


----------



## SilverFox (Sep 9, 2006)

Hello Reima,

I will get you on the list.

Tom


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## yaesumofo (Sep 12, 2006)

I am happy to see that the testing has begun again.

For those of you with wives determined to box the case trust me it is unnecessary. Simply close the case with the lights inside it and seal the case with a zip tie through each lock hole. This secures the case and prevents it from being tampered with.
I ship equipment with far greater value than our light set on a regular basis using common carriers (FED EX UPS and USPS). In these pelican cases. They are able to take the abuse from luggage carriers and postal workers alike with ease.
Just seal and ship. If somebody is really motivated to do something different then go down to FED EX and get a "bib" which is a plastic sheet which attaches to the case for the purpose of the shipping label. Being that ours is so small a bib is a good idea.
Yaesumofo


----------



## Codeman (Sep 12, 2006)

yaesumofo knows what he's talking about. I shipped my personal laptop from Saudi Arabia back home in a Pelican 1550 (along with a tape drive) and every arrived in perfect condition. Except for a couple of scuff marks, the case was as good as new.

Thanks again for providing the case, yaesumofo! These lights certainly deserved it.


----------



## georges80 (Sep 21, 2006)

Ok, my turn (modamag dropped of "the box" yesterday).

LM631 S/N 0309165

Followed warm up instructions for the lights, ~70F room temp, dark ambient.

White 1120 lux
Green 2700 lux
Blue 220 lux
Red 770 lux
Surefire 2350 lux

Certainly taking a look at the results we have so far confirms the Sphere Optics claim that our lightmeters are quite inaccurate for LED measurements, especially across the spectrum.

Using an InternationalLight Radiometer (calibrated Jan 2006):
Model IL1400BL S/N 7965

Sensor/filter/optic:
SEL033 S/N 8450 (Filter F #29226, Optic W #11693)

The following readings were taken, dark room, 1m distance between light and radiometer sensor surface. The light beam under test was swept across the sensor to get the peak reading.

White 230 uW/cm2
Green 250 uW/cm2
Blue 245 uW/cm2
Red 505 uW/cm2
Surefire 3370 uW/cm2

george.


----------



## Bullzeyebill (Sep 21, 2006)

Notice that George's readings and mine are pretty close. Both of our LM631's are 03.

Bill


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## Reima (Sep 23, 2006)

SilverFox said:


> In Puerto Rico
> Reima
> 
> Tom



I just that I would point out that Puerto Rico is in the US.
RC


----------



## NextLight (Sep 28, 2006)

Lights recv'd today. I am warming up batteries as we speak, and will edit this with data ASAP.

Thanks


----------



## wasBlinded (Sep 28, 2006)

George -


Aren't Lux and Lumens weighted for visual brightness? I don't think there is a linear relationship between radiated power and lux or lumens so its hard to draw conclusions with the information presented.


----------



## georges80 (Sep 28, 2006)

wasBlinded said:


> George -
> 
> 
> Aren't Lux and Lumens weighted for visual brightness? I don't think there is a linear relationship between radiated power and lux or lumens so its hard to draw conclusions with the information presented.



Yes. The lightmeters we use are photopic in response, i.e. they are purposely filtered to "try" and respond to light intensity/spectrum as our eyes would.

The TROUBLE is that most white LEDS that we are interested in (Luxeons etc) use a phospor to 'fake' white and the spectrum is VERY peaky in areas that our eye is less sensitive to. The light meters we use (they are pretty cheap) tend to have large variations in accuracy when it comes to the wavelengths that the designer knows our eyes aren't to sensitive to. But, due to the way the white light is 'made' those spectrum peaks are important. So, what we see is a large lightmeter to lightmeter variation in 'reported' lux/lumen as has been made obvious from the plots of the data we've collected so far.

I only took the radiometer readings (which are relatively flat across the visible spectrum) to provide an indicator of what the true light output, from an energy point of view, we are getting from the various lights/colours.

cheers,
george.


----------



## bwaites (Sep 28, 2006)

I haven't looked at this thread since the lights were certified, (I just forgot about it).

A Pelican case to ship in!

Wow, I thought the whole point of LED's was there shockproof durability?

I tease milkyspit all the time about how he ships stuff to me wrapped in multiple layers of bubble wrap when the lights are HA3 and supposedly durable as all get out. 

I mean, my brother in law carried an A2 for a year in Baghdad, clipped to his pocket. He was a mechanic there, so his light was under, over, inside, etc of big equipment, tanks, trucks, etc. He never even had to replace the lamp!! Went through dozens and dozens of cells.

And here we are with these HA3 lights acting like they are fragile! As long as they have something between them to keep them from rubbing on each other, you should be able to drop them in one of those non-rip envelopes and all is good!

Bill


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## SilverFox (Sep 28, 2006)

Update:

I have added George's readings to the data in the first post.

It seems we have lost a few people and others have been rearranged. I believe Jonathan (Modamag) has already done the tests, but I did not receive his test results. McGizmo is busy getting his new workshop in order, so we are just about done with the continental US.

I want to get the lights back for general maintains before we ship off continent. The A2 has a couple of broken contacts in the tail cap and I am interested in trying a new lamp to see how much it effects the readings. I may end up sending along a replacement lamp when the lights are sent to Puerto Rico and, if there is still interest, abroad. I know Peu in Argentina is interested.

NextLight,

I believe Robstarr-Lite should be the next in line. 

I will get in touch with Larry (Tvodrrd) to see if he still wants in, and will get the results from Jonathan (Modamag). I will also contact NewBie to see how his schedule is shaping up. 

As I find out more information, I will update the schedule in the first post.

Tom


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## modamag (Sep 29, 2006)

Sorry for the late posting guys here are the numbers.

Meterman LM631-0503028
Garage temperature @ 69.2F
All new fresh batteries BS-CR123 & Ti-CR123.
Repeatable (+/-50lux) & similar results between diff batteries & iteration.

Average reading:
A2 Incan	- 2334 lux
A1 / White	- 940 lux
A1 / Blue	- 867 lux
A1 / Green	- 1273 lux
A1 / Red	- 2346 lux


Basically all this is telling me is that our investment is pretty much useless.
It's only good for a quantitative comparison between different lights when using the same meter. So the only thing we can say from our lux reading is ... "hum my modded U-bin is brighter than my T-bin", which most of the time our ceiling bounce test will tell ya. Too bad I can't say it's 25% greater intensity.

Now if only we can take it to the next step and get our meters calibrated against a standard ... I guess I'm still dreaming of a cheap IS.


----------



## NextLight (Oct 1, 2006)

Anyone else had trouble with consistiency-repeatability?

I have run thru the specified test cycles 5x3 times. Starting with fresh SF 123As at room temp, I see variations of around 20% from reading to reading with my meter. The LED lights seem to be especially voltage sensitive, which surprises me. The hot spots in the beam pattern(s) are difficult to pick out, and are NOT in the center of the beam on some of the heads. It takes a couple of minutes to get a real peak with confidence. 

If I am going to have 20% variation on a given light in a specified condition, plus about 20% absolute uncertainty, I don't have much of a meter, IMO. (LM 631 SN 0507003)

Any advice?


----------



## SilverFox (Oct 1, 2006)

Hello NextLight,

I have not noticed any problems... perhaps its time to do some contact cleaning. 

When I did my initial testing, I took everything apart and moved the meter to a different location. There was some minor deviation, but not as much as you are seeing.

Let us know what you come up with.

Tom


----------



## Codeman (Nov 15, 2006)

Tom, can you add me to the end of the list? I've changed my setup at home a bit, and would like to re-test after everyone else has completed their testing.


----------



## Reima (Nov 23, 2006)

RC


----------



## Bullzeyebill (Nov 24, 2006)

I like the idea of calibrating our lightmeters. Can be do it ourselves. Calibrate them to LSI results? Might work only for incan results, or led results, but our colors results were all over the map. I tend to be more interested in bounce with lightmeter, than lux.

Bill


----------



## SilverFox (Nov 24, 2006)

Hello Ray,

The lights are currently headed my way. I am going to do some maintenance and cleaning on them, then organize round 2 of this testing. I believe there are some people outside of our 50 states that are interested in checking their meters.

I am planning on getting round 2 going after the first of the year. I will see if I can squeeze you in before that, or after if that works better for you.

Tom


----------



## SilverFox (Nov 24, 2006)

Hello Reima,

I believe you are interested in testing, is that correct?

Tom


----------



## SilverFox (Nov 24, 2006)

Hello Bill,

I don't know about an actual calibration, but you should be able to come up with very close ballpark correction factors for your meter. Just don't re-paint the ceiling used for the bounce testing...  

Tom


----------



## Reima (Nov 24, 2006)

SilverFox said:


> Hello Reima,
> 
> I believe you are interested in testing, is that correct?
> 
> Tom


Yes, that is correct.
RC


----------



## yaesumofo (Dec 4, 2006)

I am glad to see that after some major delays and the like, that the project slloos like it will be back on track in the new year.

I know this may sound silly but maybe at the end of the tests we should have the lights sent back to the calibration shop to determine if there had been any change in outputs on the standards.
Just a thought.

I am just happy to see this keep going.
Yaesumofo


----------



## yaesumofo (Dec 4, 2006)

doubble


----------



## Codeman (Dec 4, 2006)

SilverFox said:


> Hello Ray,
> 
> The lights are currently headed my way. I am going to do some maintenance and cleaning on them, then organize round 2 of this testing. I believe there are some people outside of our 50 states that are interested in checking their meters.
> 
> ...



After would be fine. I think first-timers ought to get them before any second-timers. :goodjob:


----------



## jch79 (Dec 4, 2006)

I wouldn't mind being added to the list either - I've been doing my own testing with an LM-631, and would find it interesting how mine compares to others.
Thanks,
john


----------



## Lurveleven (Jan 19, 2007)

SilverFox said:


> The lights are currently headed my way. I am going to do some maintenance and cleaning on them, then organize round 2 of this testing. I believe there are some people outside of our 50 states that are interested in checking their meters.
> 
> I am planning on getting round 2 going after the first of the year. I will see if I can squeeze you in before that, or after if that works better for you.



Hi Tom,
I don't have a light meter yet, but if I buy one could I get them to ship it to you and then you could test it since you already have the lights? When do you expect round 2 to begin? (So I know how fast I need to decide on what meter to get).

Sigbjoern


----------



## SilverFox (Jan 19, 2007)

Hello Sugbjoern,

Markcm has the lights right now. I think he is almost done with them. I was thinking about starting round 2 around the first of February. 

Tom


----------



## LuxLuthor (Jan 23, 2007)

I'm not sure if I should start a new thread about this, but I did not see any other threads that had as much information on light meter testing as this one. I know the setup information in this thread was for the specific light testing...but I'm wondering about the best way to do a wider variety of light meter testing.

I just bought a new Meterman LM631 for $85 from this site. I mainly wanted to compare the relative output of my many LED and incan lights, including if possible, ones like the Barn Burner, various MagLite mods, SF-L2, SF-M4, etc. etc.

First, I'm not sure if this meter can measure the stronger lights without it going overlimit, but if I can...what would be the best way to standardize the setup with such a wide variety of lights?

I mean in terms of details like ambient light (or total darkness), put Meterman sensor on whitewall and set it for Peak Max, should I go beyond the 1 foot/meter guideline for fc/lux readings, because some of my lights are so bright, etc. etc.

I'm also most used to people talking about the bulb ratings of the incan lights...like the WA maglites for example. I'm not exactly sure how to compare torch lumens with lux or fc. 

Sorry for being such a noob about this.


----------



## Mike abcd (Jan 23, 2007)

I bought a used Extech meter off eBay. It doesn't have a model # on it but appears to be an earlier version of their current 401025. Same switch setup, layout and ranges but it doesn't have the zero adjust of the current version.

I've checked it with5 LED lights with published reviews and get good agreement. If you'd like another Extech data point, you can add me to the list if you're willing to notify me by e mail.

Mike


----------



## LuxLuthor (Jan 23, 2007)




----------



## SilverFox (Jan 23, 2007)

Hello LuxLuthor,

Here is one of the best reference books on light measurement.

You may find that measuring highly columated lights can be a little difficult. There often is a crossover point in the beam which can throw your measurements off. I generally find that I get better results when I take the measurements at greater distances. Once you have a measurement at 5 meters, you can "normalize" the readings for 1 meter for comparisons.

There have been "issues" with the peak hold on the Meterman meters. You may want to read back through this thread to learn about them. Most people don't use it.

A white wall, and ceiling, can inflate your readings. Reflected light should be eliminated as much as possible. I take my measurements in the dark.

Tom


----------



## LuxLuthor (Jan 24, 2007)

SilverFox said:


> Hello LuxLuthor,
> 
> Here is one of the best reference books on light measurement.
> 
> ...




Many thanks for that. Exactly what I was hoping to hear & read. Which meter would you recommend after all your reading and experience? I'm not as sure on the Meterman now. 

Now time for some reading of that pdf ! :goodjob:


----------



## SilverFox (Jan 24, 2007)

Hello LuxLuthor,

Lighting Sciences Inc may be able to build you one of their meters, but it is expensive. I seem to remember them running in the $3000 - $5000 range, and you should send it in for an annual calibration check.

With an integration sphere ($12000+) you can also get lumen measurements.

When you check the meters used in the benchmarking testing, you find that most of them did very well with incandescent light. The colors are what threw the meters off the most. 

Tom


----------



## soffiler (Jan 24, 2007)

When I did some research on light meters a while back, I learned that even the low-budget models actually do pretty well on the higher wavelengths (yellow, red) which just so happens to be what sunlight and incandescent light is largely composed of. They run into accuracy problems with lower wavelengths (blue, purple) which unfortunately is a major component of fluorescent lamps and white LED's.


----------



## LuxLuthor (Jan 24, 2007)

soffiler said:


> When I did some research on light meters a while back, I learned that even the low-budget models actually do pretty well on the higher wavelengths (yellow, red) which just so happens to be what sunlight and incandescent light is largely composed of. They run into accuracy problems with lower wavelengths (blue, purple) which unfortunately is a major component of fluorescent lamps and white LED's.



Interesting info. Hey btw, love that work light you have on your site. Cool looking. What's the lumen output?


----------



## bwaites (Jan 24, 2007)

Output is 105 lumens if I remember correctly.

Oops, just checked, it's 104 lumens.

PM sent, Lux.

Bill


----------



## soffiler (Jan 24, 2007)

Bwaites, thanks for jumping in. 104 is correct, and I'll also point out those are engineering lumens not marketing lumens! In other words, an actual 104 was measured in an integrating sphere on a actual working unit, so that number includes the losses in the reflector/optic (which were designed for the best efficiency possible).

LuxLuthor, thanks. For the flashaholic, possibly the most interesting feature is the beam pattern. We went out of our way to create a beam that is 100% "sidespill", with literally no center hotspot and no "throw". As a worklight, which is what CentraLED is, this means your whole work area is illuminated evenly. I believe Flashlightreviews has a beamshot, and I believe we still have a CPF special - check the sticky in Dealer's Corner.


----------



## bwaites (Jan 24, 2007)

Steve, 

No problem, didn't know when you might have a chance to get back.

They are great lights, although mine seldom gets used. I have to cycle the batteries to make sure they stay in shape!

Bill


----------



## bwaites (Jan 24, 2007)

Steve, 

No problem, didn't know when you might have a chance to get back.

They are great lights, although mine seldom gets used. I have to cycle the batteries to make sure they stay in shape!

Bill


----------



## Lurveleven (Mar 12, 2007)

SilverFox was kind enough to test my meter, an Extech Datalog 401036, and got the following results:

A2 Incandescent - 2330 lux
White LED - 1190 lux
Blue LED - 70 lux
Green LED - 2430 lux
Red LED - 1700 lux

Sigbjoern


----------



## N162E (Apr 7, 2007)

Lurveleven said:


> SilverFox was kind enough to test my meter, an Extech Datalog 401036, and got the following results:
> 
> A2 Incandescent - 2330 lux
> White LED - 1190 lux
> ...


I have the same meter. Interesting to note that my tests (Post #301) with the exception of the red were all within a few percent of yours'. The red being the extreme was only different by about 12%.


----------



## mattchase (Jun 8, 2007)

Are these lights still available for testing? I just bought a CEM DT-1309 meter and am wondering how accurate it is. If this meter is up to snuff then it might be of great interest to everyone as it includes a USB cable and data logging software for the PC, yet the whole kit only costs about $100.


----------



## Codeman (Aug 15, 2007)

Good question, Matt. I was hoping to get the lights a second time, now that I've improved my testing setup/technique.


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## Curious_character (Aug 20, 2007)

I've been using a $30 eBay light meter (brand name is in Chinese characters) for quite some time. But, as my _nom de lume_ implies, I've always been *curious* about how inaccurate it might be. I've also been dinged several times when I've posted lux measurements, by people whose readings or assumptions were in conflict with my measurements. So I broke down and got an Extech 401036 with NIST certification.

I've now run a few side-by-side tests of the two meters. Lights were a selection of various beam patterns and output levels. About half had Cree emitters and half had SSC, most of which I'd modded into former Lux lights.

In 14 readings over nearly a 20:1 range of light levels (all on the same scale, the one I most often use), the cheap meter consistently read higher. But the maximum difference was only 13%. One measurement was off by only 2%, and the average difference was 7.3%.

I measured only one 5 mm LED light, and the difference there was 25%.

Of course this can't be extrapolated to infer that all cheapo meters are accurate. But it sure shows that at least one is pretty darn good.

c_c


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## soffiler (Aug 20, 2007)

c_c:

Out of my own curiousity, what light source is used for certifying to NIST? And how well did your 401036 perform? (I am about to place an order for one myself, although the primary use is for runtime testing where absolute accuracy is less critical) 

If the NIST cert uses incan, then I'm not sure you're proving much of anything when using LED's to compare the $200 meter and the $30 meter. As you probably know, LED's have a spectrum that is markedly different from incan - LED's are very heavy in blue and deficient in red, where incan are light in blue and heavy in red (and on into infrared). Inexpensive photometric sensors can be tweaked in various ways to produce decent reading vs. a reference standard, but those very tweaks are going to throw the meter off when using other types of light sources.


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## Bullzeyebill (Aug 20, 2007)

soffiler, I know this is a long thread, but. I think your answers are somewhere in this thread.

Bill


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## cy (Aug 20, 2007)

ahh... an oldie but goodie thread!


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## Curious_character (Aug 20, 2007)

soffiler said:


> c_c:
> 
> Out of my own curiousity, what light source is used for certifying to NIST? And how well did your 401036 perform? (I am about to place an order for one myself, although the primary use is for runtime testing where absolute accuracy is less critical)
> 
> If the NIST cert uses incan, then I'm not sure you're proving much of anything when using LED's to compare the $200 meter and the $30 meter. As you probably know, LED's have a spectrum that is markedly different from incan - LED's are very heavy in blue and deficient in red, where incan are light in blue and heavy in red (and on into infrared). Inexpensive photometric sensors can be tweaked in various ways to produce decent reading vs. a reference standard, but those very tweaks are going to throw the meter off when using other types of light sources.


According to the NIST calibration sheet, calibration was done with a tungsten light source of 2856 degrees K, using calibration procedure EICM401036-CP. Two traceable standards were used, a Konica Minolta T-10 illuminance meter and a Minolta XY-1 chroma meter. The error shown for my meter ranged from 0.3% on the most sensitive scale to 1.04% on the least sensitive scale. (Spec is +/- 3% + 5 digits.)

What I think I'm proving with the comparison is that the two meters read very nearly the same when illuminated with an LED source. Lux level must certainly be largely a matter of definition simply because of the problem of reducing the complexity of a measurement over a range of spectra to a single number. The photopic response, which the meter has, seems to me as reasonable way to define it as any. But I'm sure some marketeers are eager to promote alternate definitions to make their products look better. Is there, or should there be, some alternate definition of light intensity for LEDs than one taken through a photopic filter, as the meter does?

I'm frankly not very interested in how the meters compare with incandescent sources, since all my measurements are with LEDs. The various lights I tested had different tints, so they did have a variety of spectral outputs. But they do, as you say, have some fundamental characteristics in common.

I'm not at all an expert on light, but hopefully I'm slowly learning.

c_c


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## soffiler (Aug 21, 2007)

Curious_character said:


> According to the NIST calibration sheet, calibration was done with a tungsten light source of 2856 degrees K, using calibration procedure EICM401036-CP. Two traceable standards were used, a Konica Minolta T-10 illuminance meter and a Minolta XY-1 chroma meter. The error shown for my meter ranged from 0.3% on the most sensitive scale to 1.04% on the least sensitive scale. (Spec is +/- 3% + 5 digits.)


 
Thanks for the detailed response.




> ...Is there, or should there be, some alternate definition of light intensity for LEDs than one taken through a photopic filter, as the meter does?


 
No, I certainly don't think an alternate definition of light intensity is in order. My point, really, was that the response of the hobbyist-quality meter is only approximately photopic. I thought maybe you were making an underlying assumption that the meter's response tracks the photopic curve precisely. Unfortunately, that is not generally true. They have particular problems in the blue part of the spectrum, which is no big deal on incan because they don't have a lot of blue content. The fact that they are certified on an incan source means issues in the blue range are not highlighted. It *is* a big deal with LED because they have a big spike in the blue range caused by the blue die under the phosphor.



> ...I'm frankly not very interested in how the meters compare with incandescent sources, since all my measurements are with LEDs. The various lights I tested had different tints, so they did have a variety of spectral outputs. But they do, as you say, have some fundamental characteristics in common...


 
Variations in LED tint occur largely in the yellow, red, and green ranges of the spectrum due to minor tweaks in the phosphor composition. Hobbyist-quality light meters do pretty well up there. I'd conclude that two of these meters that have good agreement on a variety of different LED sources have similar errors, rather than concluding that the agreement is an indicator of accuracy.


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## Codeman (Aug 21, 2007)

When you look at the results of our testing, the meters actually had a smaller standard deviation on the white LED than on the incandescent.

That was a surprise to me. But a welcome one. It means that, while the meters may not take into account the LED's blue spectrum, they still measure LED output in a meaningful way. It may not be an accurate and absolute number, but direct lux readings don't provide that for any light source anyway. What the meters do provide, however, is a reliable way to compare LED's and, when combined with consistent and repeatable testing techniques using a light meter / light box setup, they also provide a way to reasonably infer lumen output (5-7% accurate in my case).

While the spectrum issues with LED do exist, they don't invalidate the usefulness of using a light meter that is calibrated for daylight/incand. In fact, I believe that they provide a good way to approximate an LED's output in a way that relates to human eyesight, which is what calibrated meters are designed to do, _by ignoring the spectral abnormalities of LED's_. After all, what most of us want in most cases are LED's that provide good output that our eyes interpret as white light. If meters were calibrated to take into account the spectral pattern of LED's, they would actually move away from that goal, making them less useful to most of us.

As long as variations exists in the spectral patterns of various LED's, no meter will ever be capable of providing a calibrated standard that is as accurate as those based on daylight. So why chase after one? If I were a manufacturer, I'd have some compelling reasons for doing so, but as an end-user, there's no benefit, except as a pursuit of scientific curiosity.

Besides, If I did want to pursue spectral analysis of LED's, a light meter would not be my tool of choice to begin with. 

Okay, a one sentence post just turned into a series of rambling thoughts. I'm not even sure what I said will even make sense to anyone else.

I want some coffee...


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## Curious_character (Aug 21, 2007)

soffiler said:


> Thanks for the detailed response.
> 
> 
> 
> ...


I'm not trying to beat a dead horse, but rather trying to learn more about this, so please bear with me. I think you're saying that the ExTech meter is likely inaccurate when measuring LEDs because of the different spectral content of LED and incandescent light, and that the meter's response doesn't follow the photopic curve in the blue region. That sounds reasonable to me. I've been believing believing that the results would be accurate -- really, by definition -- if the meter had a truly photopic response, regardless of the spectral content. Is that also correct?

The meter came with a graph showing the meter response along with the C.I.E. photopic curve V(lambda). The match is perfect as well as I can read the graph (within a couple of percent) from 420 to about 500 nm. At longer wavelengths, there's some deviation, becoming a maximum of what looks like about 20% at around 600 nm. (The mismatch appears to be more of a slight shift in the detector peak wavelength and slight broadening of its spectral response than a general amplitude error.) The match is again very good at and above about 650 nm. If this is true, the meter follows the photopic response curve very well in the blue range. (They do claim that the "silicon photo-diode meets C.I.E. photopic curve V(lambda).) So it appears to me that the meter follows the photopic curve very well in the blue light region, and except for the deviation at around 550 - 620 nm, follows it quite closely over the remainder of the photopic spectrum. Apparently the agreement is close enough for them to make their claim about "meeting" the standard photopic curve. If this is so, then I'd think that its results should be correct regardless of the source spectrum. If I'm wrong about this, I'd appreciate your being patient and making one more try at explaining why.

If I do understand this correctly, then it would seem to follow that the cheap meter must have a nearly photopic response also. Otherwise I'd expect it to show more variation from light to light, and a larger overall measurement difference from the ExTech.

c_c


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## soffiler (Aug 21, 2007)

c_c:

Based on your description of the spectral response of the Extech, then you can scratch my earlier comments about issues in the blue part of the spectrum. I think you DO understand correctly!


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## Curious_character (Aug 21, 2007)

soffiler,

Thanks very much for your patience. I've learned a lot.

c_c


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## SilverFox (Aug 22, 2007)

Hello Curious character,

So, if your meter is properly calibrated and has the correct response, you should get the same values as the laboratory got with the CPF benchmarking lights...

Tom


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## Curious_character (Aug 22, 2007)

SilverFox said:


> Hello Curious character,
> 
> So, if your meter is properly calibrated and has the correct response, you should get the same values as the laboratory got with the CPF benchmarking lights...
> 
> Tom


I wouldn't count on it, unless I tested the same lights with the same batteries at the same distance. There seems to be quite a bit of variation from one individual light to another -- I get quite different readings, for example, from three L0D CE lights I have. There's also a wide variation between brands of batteries and maybe even between batches of the cheaper ones. A good regulator should minimize the latter, but not all lights are well regulated.

I've also seen quite a few people reporting unusual results when doing measurements of tight-beam lights at one meter. I've found it necessary to measure at a greater distance and normalizing to one meter in order to get consistent results.

My main field is electronic design, and I do consulting work in the fields of antennas and electromagnetic compatibility. I've learned that even the simplest seeming measurements are exceedingly difficult to do with even moderate accuracy -- there are many more variables and potentially confounding factors than most people realize. Even test labs with the best equipment and methodology can produce significantly different results. But nearly everyone overestimates the accuracy of his measurements. I suspect that the same is true in this field. It seems easy and straightforward to me, but that's almost certainly due to my very low level of knowledge of all the factors involved. Until and if I gain a lot more understanding, I can't make any claims about the accuracy of my measurements or repeatability by others, even though they're now being done with a meter of reasonable quality and accuracy. But I hope that they're of some use to other hobbyists nonetheless.

c_c


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## Bullzeyebill (Aug 25, 2007)

Read the whole thread. Interesting. Lumen ratings of sample lights done by lab were provided to some participants of LMBT.

Bill


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## ernsanada (Aug 31, 2007)

To everybody who took the readings.

How long did you wait before actually taking the readings. Was the readings taken right when the light was turned on or did you wait a little, like how many seconds?


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## Codeman (Aug 31, 2007)

The timing was left up to each person, if memory serves. Some may have checked it immediately after turning each light on, others waited for some time - 2 minutes, maybe something else. It just depended on each person's normal routine.

Given all of the other sources for error - meter accuracy, cell brand/charge state, testing technique, etc - I doubt the difference between checking immediately vs waiting for the light/battery to stabilize would be very significant or noticeable. But, that's just my opinion.


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## Curious_character (Aug 31, 2007)

Codeman said:


> The timing was left up to each person, if memory serves. Some may have checked it immediately after turning each light on, others waited for some time - 2 minutes, maybe something else. It just depended on each person's normal routine.
> 
> Given all of the other sources for error - meter accuracy, cell brand/charge state, testing technique, etc - I doubt the difference between checking immediately vs waiting for the light/battery to stabilize would be very significant or noticeable. But, that's just my opinion.


It's very significant, and very possibly the most variable factor. You'll see from the run time graphs that most lights have a considerable drop in output during the first few minutes. It can be due to LED or circuit heating as well as battery voltage drop. The amount of battery voltage drop depends a lot on the battery type and, in the case of a rechargeable battery, how long it's been since it was removed from the charger. I've adopted the standard practice of making single measurements 15 minutes after turn-on with a fresh battery, since nearly all the lights I have are fairly stable by that time. But I've never heard of anyone else doing this.

c_c


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## Codeman (Aug 31, 2007)

Curious_character said:


> It's very significant, and very possibly the most variable factor. You'll see from the run time graphs that most lights have a considerable drop in output during the first few minutes. It can be due to LED or circuit heating as well as battery voltage drop. The amount of battery voltage drop depends a lot on the battery type and, in the case of a rechargeable battery, how long it's been since it was removed from the charger. I've adopted the standard practice of making single measurements 15 minutes after turn-on with a fresh battery, since nearly all the lights I have are fairly stable by that time. But I've never heard of anyone else doing this.
> 
> c_c



Without knowing the exact technique each person used, we can't know that it's the most variable factor. As I've learned, and as you've mentioned elsewhere, good technique isn't easy. As you correctly point out, the amount of initial sag varies quite a bit depending on cell brand (type didn't play into this because all testing was done with primary CR123A cells) plus other facotrs. If one person used cells that drop rapidly and measured right at the start, while another waited 2 minutes with cells that don't drop as rapidly, they're readings are going to be closer than if they had both measured at the same time, or if they had used the same brand/batch of cells, or both.

But, the A2, with it's regulated incandescent light, doesn't exhibit a noticeable sag. So, in that particular light's case, the timing of when the measurement was made is actually not important at all. The other lights don't drive the LED hard, so the sag is minimized by design as well when compared to higher current level lights where the sag is more apparent. The sag, after all, is a function of not only the cell's ability to maintain constant output, but how the light manages variation in the cell output.

For those who may or may not have caught it in the first post and preceding thread, the purpose of this testing was to learn how to better measure and to learn why different people's measurements of same model lights vary. In order to learn that, some aspects of the test where standardized, such as measuring at 1 meter, while others were left up to the user. Had everything been standardized, we wouldn't have had the opportunity to learn how to improve our individual techniques or to understand why our measurements vary from others - we would have simply been determining the accuracy of our meters when used to compare lights. While that is a worthy goal, it wasn't our goal.

Personally, I think the approach that SilverFox laid out and the rest of us had input into, was a well-thought out one in every aspect. After all, this was a learning exercise, not a scientific endeavor.


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## Curious_character (Aug 31, 2007)

I'm sorry I joined CPF after this took place. I've seen the results, which are as revealing as they are disappointing.

It's interesting that one meter was chosen as a standardized measurement distance. I don't know anything about the beam pattern of the measured light, but I've found it very difficult to make repeatable measurements at one meter with lights having a tightly focused beam. I make most of my measurements at about three meters, and even that gets tricky with something like an MRV. I've made this comment on several threads, but haven't heard anyone else mention having a problem at one meter. Does the tested light have a fairly broad beam with fairly uniform brightness over the whole hot spot area?

c_c


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## Codeman (Aug 31, 2007)

No, they don't. They all have a "typical" hot spot with flood/spill. Most folks around here just measure spot intensity, as that's the easiest thing to do, since integrating spheres aren't exactly cheap fare!

If you search the Flashlight Review forum for Surefire A2, and Flashlight Review forum and the McGizmo forum for the Aleph (or Aleph 1) light, you should find beamshots for the lights we used.

The lights we used all have a well-formed hot spot at 1 meter, and that tends to be the most common distance used on CPF (tradition?). If we'd had a Lux V-based light with a larger reflector, 1 meter would definitely be too close. You're are definitely correct for some lights - 1 meter can be too close. I had to go out to 3 meters for my USL, partly due to the spot not being well-formed at 1 meter, but also because my meter simply couldn't handle the output at 1 meter. A 50k+ lux spot can't be handled by a 20k lux meter without relying on the inverse square law!

You're also correct that a tightly focus beam can be a bit difficult to get consistent readings at 1 m. But, besides tradition, it's a distance that most of us can accomodate easily. Using a dark baffle around the light, light path, and meter, also helps. Well, bafffle isn't the right word - maybe dark light path container is more descriptive. I built a black tube that holds the meter at one end and allows me to somewhat accurately place the light at the other end so that stray light from the spill is greatly reduced, and the point of focus is more constant. As I'd been told, that really helped me to get more consistent measurements. Just how much it helped, is yet to be seen. But I should know soon...

Once the environment around a light/meter testing is stable, and all of the other variables (such as when to measure, aim, lack of ambient light, etc) are held reasonably constant, 1 meter readings for well-formed, even tight, beams can be made. Assuming that 5-10% is good enough. For better accuracy, a lot of things do need to be changed/improved, but for most of us, such changes are either beyond our interest level, or financial means. Sharing in the cost of lab measurements for these lights, though, helped us to get a feel for how our humble testing setups compare to reliable, scientific data on these lights.

There is one advantage to using lux @ 1m. By taking the square root, you have the distance at which a given light's spot can "throw" light at an output of 1 lux. That's quite helpful in quantifying how multiple lights compare in regards to "throw", as it a bit more objective than statements like "light X outhrows light Y by blahblah amount".

A few of us have gone a step further and use a quickbeam-style ligtbox apparatus, which is kind of a poor-man's replacement for an integrating sphere. Thanks to the benchmark testing, I've learned to measure most of my lights within 5-7% of their actual lumen output. Info on quickbeam's approach can be seen here.

BTW - many of the meters that were used are either designed to measure environmental lighting to OSHA standards, or photography, so we're actually using them outside of their intended purposes. For most folks, these sub-$100 meters are reasonably accurate with white lights, at least from a hobby standpoint, but things definitely went south where the colored LED's are concerned.

Well, after that long rambling attempt at giving some useful info, I've probably stepped on my weenie somewhere. Hopefully, someone will come along and correct me!


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## Curious_character (Aug 31, 2007)

Thanks for all the good comments.


Codeman said:


> No, they don't. They all have a "typical" hot spot with flood/spill. Most folks around here just measure spot intensity, as that's the easiest thing to do, since integrating spheres aren't exactly cheap fare!
> 
> If you search the Flashlight Review forum for Surefire A2, and Flashlight Review forum and the McGizmo forum for the Aleph (or Aleph 1) light, you should find beamshots for the lights we used.
> 
> The lights we used all have a well-formed hot spot at 1 meter, and that tends to be the most common distance used on CPF (tradition?). If we'd had a Lux V-based light with a larger reflector, 1 meter would definitely be too close. You're are definitely correct for some lights - 1 meter can be too close. I had to go out to 3 meters for my USL, partly due to the spot not being well-formed at 1 meter, but also because my meter simply couldn't handle the output at 1 meter. A 50k+ lux spot can't be handled by a 20k lux meter without relying on the inverse square law!


I'm speaking only of measuring the brightest part of the main beam. The problem I've had with tight beams is the difficulty in aiming them. When the intensity of the beam varies significantly in a distance which is on the order of the light meter aperture, it gets difficult or impossible to consistently measure the maximum value.



> You're also correct that a tightly focus beam can be a bit difficult to get consistent readings at 1 m. But, besides tradition, it's a distance that most of us can accomodate easily. Using a dark baffle around the light, light path, and meter, also helps. Well, bafffle isn't the right word - maybe dark light path container is more descriptive. I built a black tube that holds the meter at one end and allows me to somewhat accurately place the light at the other end so that stray light from the spill is greatly reduced, and the point of focus is more constant. As I'd been told, that really helped me to get more consistent measurements. Just how much it helped, is yet to be seen. But I should know soon...


What I've done is to make a disk a bit larger than the light meter aperture -- or just use my hand -- to block the main light beam, then look at the meter reading. My logic is that with the main beam blocked, I'm seeing all the light arriving by any other path. I'm satisfied that my anti-reflection measures are effective if it reads a negligible value. 



> Once the environment around a light/meter testing is stable, and all of the other variables (such as when to measure, aim, lack of ambient light, etc) are held reasonably constant, 1 meter readings for well-formed, even tight, beams can be made. Assuming that 5-10% is good enough. For better accuracy, a lot of things do need to be changed/improved, but for most of us, such changes are either beyond our interest level, or financial means. Sharing in the cost of lab measurements for these lights, though, helped us to get a feel for how our humble testing setups compare to reliable, scientific data on these lights.
> 
> There is one advantage to using lux @ 1m. By taking the square root, you have the distance at which a given light's spot can "throw" light at an output of 1 lux. That's quite helpful in quantifying how multiple lights compare in regards to "throw", as it a bit more objective than statements like "light X outhrows light Y by blahblah amount".


I'm afraid I'm being misunderstood when I promote measuring at a greater distance. I always normalize my readings to one meter by using the square law. So I'm not promoting quoting lux figures at other distances, just making the measurement at a greater distance. Lux at one meter equals candelas (candlepower) which is a distance-independent and universally understood value. And it has, as you say, the added advantage of simple "throw" calculation.



> A few of us have gone a step further and use a quickbeam-style ligtbox apparatus, which is kind of a poor-man's replacement for an integrating sphere. Thanks to the benchmark testing, I've learned to measure most of my lights within 5-7% of their actual lumen output. Info on quickbeam's approach can be seen here.


I've been doing that for a long time now, and it's been very, well, enlightening. But I've learned to never quote the measured values in a posting. People want very badly to believe the manufacturers' inflated claims, and every time I've posted an approximate lumen measurement, it only draws a lot of flak from folks who want to believe that their lights are as bright as the manufacturer claims. The last thing they want to hear is that their "170 lumen" light is only putting out 110.



> BTW - many of the meters that were used are either designed to measure environmental lighting to OSHA standards, or photography, so we're actually using them outside of their intended purposes. For most folks, these sub-$100 meters are reasonably accurate with white lights, at least from a hobby standpoint, but things definitely went south where the colored LED's are concerned.


I've now got a NIST-certified ExTech meter with claimed photopic response as well as a $30 eBay meter. As you say, the eBay meter does quite well with white LEDs. I don't have anything very high intensity in other colors for comparison, but when I get a chance I'll try filtering an incandescent light to get some different colors and see how they compare.



> Well, after that long rambling attempt at giving some useful info, I've probably stepped on my weenie somewhere. Hopefully, someone will come along and correct me!


Thanks again for the thoughtful and informative posting.

c_c


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## Codeman (Aug 31, 2007)

Curious_character said:


> Thanks for all the good comments.
> I'm speaking only of measuring the brightest part of the main beam. The problem I've had with tight beams is the difficulty in aiming them. When the intensity of the beam varies significantly in a distance which is on the order of the light meter aperture, it gets difficult or impossible to consistently measure the maximum value.



That's pretty much spot on. Taking the average of readings helps some with this, but it's only a small step in the right direction. For most folks, I'm not sure what else can be done, though...

This is one of the reasons I like using a lightbox. Aiming/beam variability aren't as much of an issue, assuming consistent placement of the light in relation to the lightbox.

But for getting a somewhat objective idea of throw, I think we're stuck with aiming as best as we can and averaging multiple readings.



Curious_character said:


> What I've done is to make a disk a bit larger than the light meter aperture -- or just use my hand -- to block the main light beam, then look at the meter reading. My logic is that with the main beam blocked, I'm seeing all the light arriving by any other path. I'm satisfied that my anti-reflection measures are effective if it reads a negligible value.



That seems reasonable at first blush...and cheaper than building a tube. Since I've already built it, though, might as well use it!



Curious_character said:


> ...But I've learned to never quote the measured values in a posting. People want very badly to believe the manufacturers' inflated claims, and every time I've posted an approximate lumen measurement, it only draws a lot of flak from folks who want to believe that their lights are as bright as the manufacturer claims. The last thing they want to hear is that their "170 lumen" light is only putting out 110.


The typical subjective vs objective clash! I've been greeted with silence at times on this, which is only marginally better than flak, IMO. It's refreshing to see someone else that recognizes the usefulness of the lightbox approach. Even if it isn't as accurate as a lab's IS, it's based on the same general principles. Go figure... For my money and eyes, I can't see the difference between 60 and 70 lumens, unless I have both lights on at the same time, so the inaccuracy is a non-issue for me. I would LIKE to have the accuracy of a IS at the cost of a milkbox, but that's just wishful thinking. The only lumen values that I consistently believe are Surefire's typically conserative ones, and a handful of folks on CPF with proven track records of accurate readings - McGizmo and Gransee come to mind, though I'm sure there are others that I'm either forgetting or haven't noticed.



Curious_character said:


> Thanks again for the thoughtful and informative posting.



Back at ya! I could/should have said the same about some of your recent posts.

That's a big part of what makes CPF such a fun place!

Before anyone says something about "group hugs" or "get a room", though...supper's calling...

BTW - I sent you a PM earlier...in case you haven't seen it. Hope it helps with your late arrival to this thread.


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## Curious_character (Aug 31, 2007)

Codeman said:


> That's pretty much spot on. Taking the average of readings helps some with this, but it's only a small step in the right direction. For most folks, I'm not sure what else can be done, though...
> 
> This is one of the reasons I like using a lightbox. Aiming/beam variability aren't as much of an issue, assuming consistent placement of the light in relation to the lightbox.
> 
> But for getting a somewhat objective idea of throw, I think we're stuck with aiming as best as we can and averaging multiple readings.


I'm not sure I'm communicating well. I'm talking about making lux measurements at a distance, not lumen measurements with a light box. The simple solution to the problem of beam brightness variation over a small distance is solved by making the measurement at a greater distance. That widens the main beam at the measurement plane, making it more uniformly bright over any given width.



> The typical subjective vs objective clash! I've been greeted with silence at times on this, which is only marginally better than flak, IMO. It's refreshing to see someone else that recognizes the usefulness of the lightbox approach. Even if it isn't as accurate as a lab's IS, it's based on the same general principles. Go figure... For my money and eyes, I can't see the difference between 60 and 70 lumens, unless I have both lights on at the same time, so the inaccuracy is a non-issue for me. I would LIKE to have the accuracy of a IS at the cost of a milkbox, but that's just wishful thinking. The only lumen values that I consistently believe are Surefire's typically conserative ones, and a handful of folks on CPF with proven track records of accurate readings - McGizmo and Gransee come to mind, though I'm sure there are others that I'm either forgetting or haven't noticed.


Although I can vary the light box reading some by changing the light aiming, it's not a major change. What gives me confidence in the method is that I can take something like an incandescent Mag or Mini-Mag, change the focus from a tight spot to a wide flood, and see almost no change in the light box reading. This tells me it's doing a decent job of measuring the total light. (The output from an LED Mini-Mag _does_ change as you focus it -- it puts out more light when floody than when tightly focused.) Another confidence-building test is to remove the window and reflector, resulting in a dramatically different light pattern. Typically, the light box reading drops by around 25% -- a believable loss for the reflector and window. Given that it's actually responding to the total light, it means that if my lumen estimates are wrong, they're likely all wrong by about the same factor. So at least I'm getting a fair comparison of lights. Among other things, it helps me determine:

1. How efficient the circuitry/LED combination is -- I can measure total light out per watt from the battery.
2. How tightly focused a light is. I notice, for example, that after replacing a Lux with an SSC, the lumen output is just about double but the lux reading typically doesn't increase as much -- even if I optimize the focus as best I can by moving the reflector. This tells me that the resulting light has a broader main beam and/or more or brighter spill than the original.
3. Loss in the window and reflector, determined by comparing measurements with them off and in place.
4. Comparing the outputs from different types of LEDs which have different beam patterns.

So it's another tool I find very useful in my efforts to better understand this fascinating subject. And to satisfy my. . . _curiosity_.



> BTW - I sent you a PM earlier...in case you haven't seen it. Hope it helps with your late arrival to this thread.


Got it, thanks. I'll follow up on it shortly.

c_c


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## SilverFox (Sep 1, 2007)

Hello Curious_character,

I believe this post reveals the CPF standard procedure use for the measurements during this testing.

If you are interested in how your meter matches up, let Ray know and he can ship the lights to you after he has finished with them.

Once you have finished and reported your readings at 1 meter, feel free to do the measurements again at whatever distance you feel is suitable and see how they compare.

I am the custodian of the lights, so if this time does not work into your schedule, just keep in mind that they are available should you want to check things out at a later time.

Tom


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## Curious_character (Sep 1, 2007)

Tom,

Sure, I'd love to participate. I've sent Ray a PM with my address. Please let me know where to send them after I make my measurements. I'll do measurements at one meter as well as at my standard distance. If you'd like, I can do full run time measurements quite easily with the ExTech meter. Please PM me regarding anything else (beyond the posted protocol) that you'd like me to do, and links to any other postings I should look over before I start.

Roy


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## Codeman (Sep 1, 2007)

CC - I understand what you're saying about getting consistent spot readings at 1 meter, I just don't think that the differences are that important when all other sources of error are considered. If the rest of the setup results in 5-10% error, the potential improvements of having more exact aiming would be lost anyway. It's the weakest link in the chain that breaks, not the strongest.

Whoops - told ya I'd probably made a mistake somewhere in my last few posts! I was obviously wrong about when the measurements were to be taken. 

From the first post:


SilverFox said:


> ...
> 
> 4. - The lights will be turned on for a minimum of two minutes before taking measurements. This goes for all lights.
> ...



Memory isn't what it used to be. Still, if a given user's technique isn't sound, whether they take readings right from the start or 2 minutes in can be rendered moot by other errors for those lights that exhibit a sag.


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## Curious_character (Sep 1, 2007)

I'll record the lux level for at least the first 15 minutes or half hour, to see just how much variation there is after two minutes.

c_c


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## Codeman (Sep 1, 2007)

Just be sure to complete the benchmarking tests as outlined in the first post separate from anything else you do. As far as this thread goes, that's what we're interested in. Deviating from those "standards" would skew the results for everyone.


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## Curious_character (Sep 1, 2007)

Codeman said:


> Just be sure to complete the benchmarking tests as outlined in the first post separate from anything else you do. As far as this thread goes, that's what we're interested in. Deviating from those "standards" would skew the results for everyone.


It's not clear to me how recording the light level for the first 15 minutes or half hour would be deviating from the "standard". I'd just pick from the string of measurements a value which was taken more than two minutes after turn-on to submit as the single official reading. The light meter has the recording function built in, and doesn't make measurements any differently when recording than it does when you're looking at the meter. Am I missing something here?

c_c


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## Codeman (Sep 1, 2007)

Curious_character said:


> It's not clear to me how recording the light level for the first 15 minutes or half hour would be deviating from the "standard". I'd just pick from the string of measurements a value which was taken more than two minutes after turn-on to submit as the single official reading. The light meter has the recording function built in, and doesn't make measurements any differently when recording than it does when you're looking at the meter. Am I missing something here?
> 
> c_c



You need to read the first post. We all agreed to follow those procedures as a condition of participating. Among the other requirements, runtime tests are not to be performed on these lights.

If you want to do tests beyond the specific procedure outlined in this project and SilverFox's okay for you to repeat them at a distance greater than 1 meter, then you need to do so with other lights and not participate in this project.


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## SilverFox (Sep 1, 2007)

Hello Curious_character,

Around $1300.00 was invested to have these lights certified by a lighting laboratory. This does not include the initial cost of the lights. The LED lights were built by McGizmo and donated. The A2 was donated by PK of SureFire. Several people donated funds to cover the certification, and Don and I picked up the rest of the tab.

We discourage extended runtime tests because the lights have a finite life and we are trying to get the most from our investment.

To get the best comparison results, you will need to follow the same procedures used by the other CPF members and the lighting laboratory. Those procedures are laid out in the first post of this thread.

I should also remind Ray and point out that we have agreed that when shipping these lights, the package will be insured for $500.

I will PM you with my address so you can ship them back to me after you have finished your testing. 

Tom


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## Curious_character (Sep 1, 2007)

SilverFox said:


> Hello Curious_character,
> 
> Around $1300.00 was invested to have these lights certified by a lighting laboratory. This does not include the initial cost of the lights. The LED lights were built by McGizmo and donated. The A2 was donated by PK of SureFire. Several people donated funds to cover the certification, and Don and I picked up the rest of the tab.
> 
> ...


Sorry, all I saw which I thought applied was:

---------

4. - The lights will be turned on for a minimum of two minutes before taking measurements. This goes for all lights.

5. - You should take the measurements as you normally would and report what you get. You can then do another set of measurements under tighter control and report those measurements as well if you are so inclined to do so.

---------

My proposed method was in accordance with those requirements -- I would turn on the meter, turn on the light, and after two minutes (or more), record the light level. I don't understand why having the meter record the light level for those two minutes is prohibited, but I'll leave it off since it isn't permitted. But I understand (although I didn't see it in the criteria) the requirement to limit run time, so I do see why I shouldn't leave the light on to continue recording beyond the measurement time. What's the maximum length of time the light should be allowed to be on for any test? What's the maximum total runtime allowed for all tests? I have two meters. Is it ok to do the measurements with each of the meters? I'll certainly abide by any restrictions you've set -- all I need to know is what they are.

I hope that after making three measurements each at two minutes with the recorder turned off, I'll be permitted to run the light for another two minutes with the recorder on. I was hoping to see how rapidly the light level dropped during that period and a bit beyond, until the light output was fairly stable -- my intent wasn't to do a run time test. Because the test procedure says only two minutes _minimum_, one source of measurement scattering could occur if one tester decided to measure at 5 minutes and another at two -- and if the light level changes significantly during that period. Perhaps you've already looked at that and determined that these particular lights are stable by the time they've been on for two minutes, in which case there's no need for this investigation.

c_c


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## SilverFox (Sep 1, 2007)

Hello Curious_character,

I am not sure I understand your concern...

You can run your meter as long as you want to. I usually let my meters warm up for around 5 - 10 minutes to make sure they have stabilized, then turn on the light and note the reading at 2 minutes.

The lighting laboratory was amazed at our procedure because most of their clients want the peak instantaneous reading that occurs at start up. When I explained what we were doing and how we were doing it, they agreed that waiting 2 minutes for things to stabilize made sense to them. I explained that the ability to have a repeatable measurement was more important than the actual peak momentary output of the lights.

I will trust your judgment as to how long to run the lights. Several of us used two cells for all of the tests on all of the lights, and the cells still had a lot of life left in them. I suppose we could extrapolate a general guideline from that and say that if your 2 cells run out, you are into extended runtimes...

At any rate, I promise not to turn you in to the Runtime Police...  I just ask that you be sensitive to what has gone into this project and conduct your tests accordingly.

If you take the time to read through the thread you will find references to the regulation of the lights and I believe there are some graphs showing what kind of variation in the regulation circuits can be expected. I seem to remember Don posting a graph of the Aleph regulation circuit over an extended run while he was breaking the lights in. You will have to search this thread for that graph.

Tom


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## Codeman (Sep 8, 2007)

My round two results:

A2 - 2450,2460,2470 - avg 2460, std dev 10 (-2% error)
Aleph white - 1270,1290,1290 - avg 1283, std dev 12 (1% error)
Aleph blue - 290,280,280 - avg 283, std dev 6 (88% error)
Aleph green - 2650,2640,2670 - avg 2653, std dev 15 (13% error)
Aleph red - 970,980,960 - avg 970, std dev 10 (-59% error)

Temp - 68°F.

Thanks again, Tom! :thumbsup:


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## Curious_character (Sep 16, 2007)

Here are my results:

Using an ExTech 401036 with current NIST certification:

A2: 2340, 2340, 2340 - avg. 2340, -6.7% error
White LED: 1218, 1220, 1215 - avg. 1218, -4.1% error
Blue LED: 75.8, 76.3, 77.1 - avg. 76.9, -49.4% error
Green LED: 2570, 2580, 2560 - avg. 2570, -9.0% error
Red LED: 1466, 1456, 1463 - avg. 1462, -38.6% error

Using an "L1010B" meter (brand is printed in Chinese) purchased from eBay for $30:

A2: 2460, 2440, 2440 - avg. 2447, -2.4% error
White LED: 1251, 1245, 1249 - avg. 1248, -1.7% error
Blue LED: 1386, 1386, 1389 - avg. 1387, +819% error
Green LED: 2120, 2120, 2110 - avg. 2117, -10.2% error
Red LED: 2010, 1990, 2000 - avg. 2000, -15.9% error

The $30 meter did better than the $300 dollar meter with the white and red LEDs and the A2, and insignificantly worse with the green LED. It was much worse with the blue LED, but the $300 meter was way off in that measurement anyway.

These tests were all done with the prescribed protocol. I didn't have the time to do a complete tear-down between measurements, but I did re-aim each time, and this is surely one of the major causes of variability. After making a measurement with the ExTech, I re-aimed the light slightly to center it on the cheap meter which was right beside it. Then I turned off the light, removed the head, and cooled it with a fan for about two minutes (except the A2, which was cooled in place). This is because I noted that the output from the white LED, in particular, decreased as it warmed up. I replaced the head, turned the light on, and re-aimed it during the 2 minute waiting period. With tests run before the official run, I satisfied myself that the output changed insignificantly with battery condition, so I used the same new cell for all tests except the A2. The A2 got a fresh set of two cells.

I learned something very important from these tests. I ran some additional tests at my usual distance of about 3 meters where aiming is easier. And I discovered that the square law assumption didn't work! The difference in results with the white LED light between the 1 meter and square-law adjusted 3 meter measurements was 21%! I've started a new thread on this topic here.

Doing the tests, seeing the results, and learning about the square law problem were all real eye-openers. Thanks very much to all involved for providing this opportunity!

The ExTech's recording feature is nice, but I guess when I really want accurate measurements, I'll have to put it aside and use the $30 eBay meter.

c_c


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## soffiler (Sep 17, 2007)

Hey c_c...

I don't mean to say "toldya so", but, did I not mention earlier in this thread that hobbyist-grade light meters have trouble in the blue part of the spectrum?


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## Codeman (Sep 17, 2007)

Curious_character said:


> ...
> I learned something very important from these tests. I ran some additional tests at my usual distance of about 3 meters where aiming is easier. And I discovered that the square law assumption didn't work! The difference in results with the white LED light between the 1 meter and square-law adjusted 3 meter measurements was 21%! I've started a new thread on this topic here.



Square law assumption? Last time I checked, the inverse square law is a proven bedrock of science, not an assumption. What varies is our ability to correctly conduct tests so that we can measure by those laws accurately. This is at the very heart of why we undertook this testing - being able to repeatedly measure our lights in a consistent way and get consistent results.


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## Curious_character (Sep 18, 2007)

soffiler said:


> Hey c_c...
> 
> I don't mean to say "toldya so", but, did I not mention earlier in this thread that hobbyist-grade light meters have trouble in the blue part of the spectrum?


Yes, I believe you did, and I've never had reason to doubt it. You didn't mention, however, how badly expensive meters do. 49% error isn't at all what I'd consider to be accurate, and that's all the better my ExTech did.

I have a question for the folks who had the lab tests done: Were the lab meters traceably calibrated at the wavelengths of the tested lights? Or were they only traceable to incandescent standards? If the latter, what reason would we have to believe their measurements to be any better than ours?

c_c


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## Curious_character (Sep 18, 2007)

Codeman said:


> Square law assumption? Last time I checked, the inverse square law is a proven bedrock of science, not an assumption. What varies is our ability to correctly conduct tests so that we can measure by those laws accurately. This is at the very heart of why we undertook this testing - being able to repeatedly measure our lights in a consistent way and get consistent results.


By "square law assumption" I meant the assumption that a reading at twice the distance from the front of a light should yield a lux level that's one fourth the value measured at the shorter distance. That's certainly not a bedrock of science, and I believe that for some flashlights, including the CPF standard white LED light, it's an invalid assumption. The inverse square law is derived beginning with the assumption that the light emanates from a single point and does not strike a lens or anything else on its journey to the measurement surface. Under that condition, the inverse square law follows from simple geometry. But the front of a flashlight isn't a point source, and while the LED itself is a good approximation of a point source, the reflector modifies the light's path from it.

It's vital to understand the conditions under which the "laws" we take for granted are valid, and to realize when the conditions differ from them sufficiently to make adjustments necessary. My conjecture, subject to validation or rejection based on further measurements, is that we can indeed apply the square law to these measurements in spite of the lack of a direct point light source -- but only after we've determined the location of an apparent point source from which to measure. And it's not at the front of the flashlight.

c_c


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## soffiler (Sep 18, 2007)

Curious_character said:


> ...You didn't mention, however, how badly expensive meters do. 49% error isn't at all what I'd consider to be accurate, and that's all the better my ExTech did...


 
Whoa! Your ExTech is *NOT* an "expensive" meter. I said something to the effect that hobbyist-grade meters tend to have trouble in the blue part of the spectrum but, guilty-as-charged, I failed to define what I meant by "hobbyist-grade". Let's just say a laboratory-grade photometer costs several thousand US dollars and on up into the tens of thousands. Anything in the hundreds of dollars, or below, is hobbyist grade in my book.


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## soffiler (Sep 18, 2007)

Curious_character said:


> By "square law assumption" I meant the assumption that a reading at twice the distance from the front of a light should yield a lux level that's one fourth the value measured at the shorter distance. That's certainly not a bedrock of science, and I believe that for some flashlights, including the CPF standard white LED light, it's an invalid assumption. The inverse square law is derived beginning with the assumption that the light emanates from a single point and does not strike a lens or anything else on its journey to the measurement surface. Under that condition, the inverse square law follows from simple geometry. But the front of a flashlight isn't a point source, and while the LED itself is a good approximation of a point source, the reflector modifies the light's path from it.
> 
> It's vital to understand the conditions under which the "laws" we take for granted are valid, and to realize when the conditions differ from them sufficiently to make adjustments necessary. My conjecture, subject to validation or rejection based on further measurements, is that we can indeed apply the square law to these measurements in spite of the lack of a direct point light source -- but only after we've determined the location of an apparent point source from which to measure. And it's not at the front of the flashlight.
> 
> c_c


 
Absolutely. For more discussion of "virtual point source" , see page 33 in the following link:

http://www.uni-mannheim.de/fakul/ps...ikel/Alex_Ryer_Light_Measurement_Handbook.pdf

Elsewhere in that same document (which should be required reading for every CPF'r!) there is discussion of errors that arise due to real-world departures from the point-source approximation, and it provides a rule of thumb that your nearest measurement distance should be at least five times the largest dimension of the source.


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## Codeman (Sep 18, 2007)

Curious_character said:


> ...
> I have a question for the folks who had the lab tests done: Were the lab meters traceably calibrated at the wavelengths of the tested lights? Or were they only traceable to incandescent standards? If the latter, what reason would we have to believe their measurements to be any better than ours?
> ...



You should contact SilverFox about making a donation to the cost of the lab tests. Complete results were provided to all participants who contributed to the cost of the lab results, but only to those participants.

If you think you can use a few hundred dollars worth of equipment to get better results than a well-respected lab that used calibrated equipment costing 10's of thousands, probably more, have fun...thanks for the laugh!


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## Curious_character (Sep 18, 2007)

soffiler said:


> Whoa! Your ExTech is *NOT* an "expensive" meter. I said something to the effect that hobbyist-grade meters tend to have trouble in the blue part of the spectrum but, guilty-as-charged, I failed to define what I meant by "hobbyist-grade". Let's just say a laboratory-grade photometer costs several thousand US dollars and on up into the tens of thousands. Anything in the hundreds of dollars, or below, is hobbyist grade in my book.


Thanks for the clarification. "Cheap" is certainly a relative term.

c_c


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## Curious_character (Sep 18, 2007)

Codeman said:


> You should contact SilverFox about making a donation to the cost of the lab tests. Complete results were provided to all participants who contributed to the cost of the lab results, but only to those participants.


I'll certainly do that, but not just to see the lab results. Thanks for letting me know they're available, though. (I assume this information was posted elsewhere in this thread -- I plead guilty to not having all 590 previous posts. So I appreciate your repeating it for me.)

I did offer to contribute toward purchase of a pass-around light meter with the assumption that it would improve our ability to make measurements. The experience of measuring the reference lights, along with the informative and educational comments of soffiler and others, shows that this wouldn't really be nearly as helpful as I had thought. I was envisioning something like a $300 meter, while it appears that thousands would be required. So my contribution would be better spent on supporting light pass-arounds.



> If you think you can use a few hundred dollars worth of equipment to get better results than a well-respected lab that used calibrated equipment costing 10's of thousands, probably more, have fun...thanks for the laugh!


You're very welcome. I'm always glad to help lighten things up a bit, even when it's the unintentional result of my admittedly deep ignorance about the general field of light and light measurement. Sometimes people get a bit tense when deeply held assumptions are questioned, or even when someone clueless person like me asks stupid questions, so I think some occasional levity isn't such a bad thing.

Thanks to the patience shown by everyone as I struggle to get a better understanding of this fascinating field.

c_c


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## Curious_character (Sep 21, 2007)

I want to thank Ray again for letting me know that the lab test results were available, and to Tom for sending them. After seeing how they were done, I'm laughing myself at the naiveté of my earlier question.

I didn't realize that the lab also measured and reported the total light output. I'm kicking myself for not having measured them with my Quickbeam type light box. I wonder if anybody else did this and, if so, they found any proportionality factor between lumens and lux reading which works fairly consistently. If not, I'd sure like to have another shot at them if they ever go around again!

c_c


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## Codeman (Sep 21, 2007)

You're welcome.

Yes, I did measure them with my light box. However, due to variations in each person's box, conversion factors are specific to each one. Although my values are quite different from quickbeams', for the lights that both of us have measured, my calc'd lumens come within 5-7% of his. I was also able to check against some other lights than Gransee had measured with an IS and I got the same accuracy with those model lights as well.

Prior to the CPF BM lights, I had used several Surefire lights to arrive at a conversion factor using their conservative lumen ratings. Both my results and LSI's reports on the A2/Incan confirm that Surefires ratings are conservative.


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## SilverFox (Sep 21, 2007)

Hello Curious_character,

 

If you can find the time, you really should read this whole thread. There is a lot of good information in it, as well as links to some of the more complex issues involved in measuring light.

A light meter measurement tells us something, but there is a lot more to it, as we have discovered.

Tom


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## mattchase (Sep 22, 2007)

Has anyone done this test using a CEM DT-1309 meter yet? If not I would be glad to do so.


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## Codeman (Sep 22, 2007)

Matt, the meters that have been tested are listed on the first page of the thread. Even among the same model meters, however, we've seen variations.


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## guiri (Jun 20, 2008)

Guys, quick question.

I usually only see lux or fc but where does LUMEN fit in and how do you measure that or do you convert to it?

Thanks

George


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## Codeman (Jun 20, 2008)

1 lux at 1 meter equals 1 fc at 1 foot for a point source.

1 lumen equals a uniform 1 lux over an area of 1 square meter. An integrating sphere is needed to directly measure lumens, but they cost thousands of dollars.

Wikipedia has more info.


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