LUX METER HELP/SUGGESTIONS

[Capolini]

I hope this is the right thread! I picked this over "General Flashlight Discussions?!

I am seriously considering a "Light Meter". I looked at Three models of the EXTECH, EA30/31/33? Each with progressively higher pricing and different capabilities of "Foot Candle" max. measurements.

This is where I am not clear! I know a few members about 6 or 7 months ago explained it a bit and gave me a formula how to convert to CD's and the most accurate way to do the test but I forgot!.

For the EA33 it has 99,990Fc [999,990cd]. That tells me you just multiply the Fc by 10 to convert to CD's?

Would the EA31 with 20,000Fc in Four ranges and 20,000lux in Four ranges be able to measure a TK61vn~622Kcd? Or a TN31mb certified at 470Kcd?

The EA30 States 40KFc to 400KFc for ~ $180

I would PREFER to get the EA30[$180] or EA31[$150] if it could measure ALL my lights from the PD12vn to the TK61vn!

The EA33 is listed at $280.

From what I remember it is best to measure from at least 10m. 15m or 20m may be even better[more accurate]!


Looking to spend $150 to $180,,,really do NOT want to pay $280 for the EA33!

Simple formulas and suggestions to best fit my budget and the capability of measuring my throw monsters petite[PD12vn] and large[TK61vn] would be appreciated! :thumbsup:


GRACIE MILLE[ 1000 THANKS]!

 

[StarHalo]

I'm pretty sure you just move the meter farther away to deduce an @1m number from an @5m measurement for super-throwers. But are you sure you want to spend that much just on getting a number? I'd much rather just compare how well the lights paint a distant object and put the money towards another light..

 

[Capolini]

I'm pretty sure you just move the meter farther away to deduce an @1m number from an @5m measurement for super-throwers. But are you sure you want to spend that much just on getting a number? I'd much rather just compare how well the lights paint a distant object and put the money towards another light..

thanks for the reply.

Not exactly sure If I want to spend that much money..If I do,,a light meter seems more beneficial/logical.

My thinking when I starting thinking about this was[the opposite of yours!] :laughing: I have 33 lights and have spent $4K on them and their accessories!! I really do not need another light, it would be nice to get something to measure them!

 

[StarHalo]

Fair 'nuff, diff'rent strokes. Generally speaking, you only have to put the big money towards a meter if you plan on comparing the numbers to someone else's; any basic/expedient meter will do a very good job of measuring the difference between your lights, if that's what you're after.

 

[Capolini]

Fair 'nuff, diff'rent strokes. Generally speaking, you only have to put the big money towards a meter if you plan on comparing the numbers to someone else's; any basic/expedient meter will do a very good job of measuring the difference between your lights, if that's what you're after.

That would be what I am looking for,a basic meter that is reasonably priced and relatively accurate. I wonder if a meter under $150[EXTECH31] could fit that criteria?

I forgot! The comparison would be to SB's and rdrfronty's numbers. Sb reviewed Two of my Vinh lights[a 3rd review on the way] and rdrfronty tested about 6 or 7 more of them plus my TN31mb!

In addition I would like to know the "Beam distance" of a few of my modded lights that have NOT been tested by anyone that I know of. The TK35vn, PD12vn,S200C2vn and a few others.

 

[SilverFox]

Hello Capolini,

I have the EA30 and have been quite pleased with its use.

Tom

 

[Capolini]

Hello Capolini,

I have the EA30 and have been quite pleased with its use.

Tom

Thanks! If I get one the EA30 was the one that I would pick. A little more $ than the EA31 w/ more diversification! Now I just have to learn the proper way to measure!

I noticed on the real expensive EA33[$280] that you needed to be inside or an area that is completely dark with no stray light to measure the "luminous intensity Feature[CD's]? I guess I should not worry about that unless it applies to the EA30! I live in a condo. this must be done outside,,,,I believe the EA30 has a setting to detect, calculate,display and or remove stray light from the total numbers!

 

[880arm]

Unless you're going to be doing runtime testing (see below) or doing true laboratory condition testing I wouldn't recommend going too crazy with your purchase. The EA30 looks to be a fine meter and, honestly, if you're only going to be spot-checking your lights a cheap meter may work just as well, as StarHalo mentioned earlier. Let me warn you in advance that there can be a ton of variance between your results and what you read from others and it's not all due to the meter that was used. Things like natural production variance in the light/LED, different test distances or methods, environmental conditions, etc. can all influence the results slightly.

In case it would be of use to you, the following is a description of what I have used in the past and why . . .

I started out with a cheapo $15 meter from Amazon. It was no superstar but it worked OK and suited my needs until I decided I wanted a datalogging meter for runtime tests. In general, its results were pretty much the same as what I achieved from later meters. If I didn't start reviewing lights I would probably still be using this meter.

I already had a cheap datalogging multi-meter so from there I went with the Extech 401021 which provides an output of 1mV per Fc which you can read (and record) on the multi-meter. I used this for quite a while and the light meter performed well but the software for connecting the mult-meter to the computer was terrible. Also, using this particular meter meant I had to convert the results from foot-candles to lux which was an extra step in the process. It wasn't a big deal but as I started to do more testing, I decided I wanted something different.

This led to the purchase of the Extech HD400 which is what I currently use. It can function as a stand-alone meter (with no datalogging) but the included software allows datalogging when connected to a PC. It has worked great and I have no complaints about the meter itself but, in hindsight, I wish I had gone ahead and bought the HD450 which adds some limited standalone datalogging capability.

 

[WalkIntoTheLight]

From years back, I used to use a simple technique to measure foot-candles for indoor gardening use. It's probably not accurate enough for you, but maybe someone else reading this thread would be interested.

Get a camera that has some basic manual adjustments.

Set the controls to use IS0/100 sensitivity, and F/4 aperture. (Or ISO/200 sensitivity and F/5.6.)

Get a matte white sheet of paper and hold it so the light you wish to measure is directly illuminating it. That is, shine your flashlight on it so it lights up all or most of the paper.

Point the camera at the paper (don't stand in the way of the light!), and focus on it so that the frame is entirely within the lit area on the paper.

Take an exposure reading with the camera. That is, look at how fast the shutter is going to be. Remember that you fixed the ISO and aperture, so the only thing left for the camera to calculate is shutter speed.

Take the reciprocal of the exposure. That is your foot candles. For example, if the exposure says 1/400 seconds, then the intensity of the light hitting your paper is 400 foot candles.

Multiply by approximately 10 to convert to lux.

I know it sounds like a lot of steps, but it's really easy once you do it a couple of times. It's a great way to get a rough estimate of light intensity. It becomes less useful as the light gets dim, depending on how good your camera is. But you can certainly test the light intensity from your lights out to several metres.

 

[Capolini]

880arm,

Thanks for all the info.!!

Where I am NOT clear w/ any of these is for example when they say they can measure 50Klux what is the method[distance for measurement?] and can they measure a light accurately[or at all] that is 622Kcd?

 

[hiuintahs]

I have the Extech HD450 which has data logging capability (USB port). What I did was copy Quickbeam's (flashlightreviews.com) format of a light box which is an orange juice or milk carton box (white on the inside) and then I made a top and wrapped the outside with tin foil.
http://www.flashlightreviews.com/features/lightbox_output.htm

I may have to put up a picture of it to see what I'm talking about. But at any rate it becomes a standard by which I compare lights. Mostly what I am doing is checking run time and graphing in Excel. This way I can tell which lights have the most efficiency. So I really value the memory and data logging capability.

I will say that a light like the PD35 on turbo puts out 55k lux in my setup so I have to have the meter at the 400k lux setting. Its the light bouncing off of the walls. So I really have no idea for sure what lumens a light has other than since the testing arena is the same for all of my lights, it then becomes relative to each other. I have come up with a formula that is pretty accurate to equate the lux reading to lumens based on testing lots of samples and comparing to manufacturer's stated value.

I would think that if you are going to have a light meter you need to have a test fixture (light box) that is a consistent environment, otherwise one might get different readings all the time.

I paid $175 used for the light meter and my flashlight hobby took off like crazy after buying this thing because, then I could test lights and really know how they performed against each other. I then bought and sold a lot of lights. I'm an efficiency nut and the only way to know is to do a run time graph.

 

[rdrfronty]

I have a couple meters. One is a mid level meter - Extech EA31 and the other a fairly cheap meter - Mastech LX1330B from Amazon. From my personal experience, they actually measure surprising close. So I feell as long as its not super super cheap, the meter will likely do the job that us hobbiest require.
As for the power ranges, as long as it will measure down to .1 lux and up to 10,000 lux, you should be fine. As long as the meter has different ranges. My more expensive Extech measures down to .01 lux and that was the main reason I bought it. I wanted to test low light levels in true life throw tests. Meaning, by testing a lights actually throws by standing 500-1000m down range from the light with the meter and tacking readings. Thats not typically done though, with myself likely about the only nutcase willing to do those long distant tests.
Now that meter only measures up to 20,000 lux. Sounds low, but It has never been an issue. The reason for that is because any light that will throw more than 20k, likely should be measured at a distance longer than 1m. Though generally throwers 50k and higher is when is becomes critical to measure longer distances. My cheaper Mastech measures up to 100k, so it does give me more options for those lights that are in the 20k - 50k range. Meaning I can test them at 1m, 5m, etc.
But again its really a moot point. If you have a light for example like a TN31vn that should throw in the 500k area. With a light like that, you should test 10m minimum. I usually do 15m since I usually have my brother helping me.
So lets use 15m as an example. For a light like that, you would normally set your light to the "up to 20,000" range. This might take some experimenting at first knowing what range to start in, but once you've tested enough lights, you know what type of rough numbers a light should read at certain distances. Anyways, now you need to VERY accurately measure your test distance. By accurate, I mean at a distance of 15m, you need to to keep the bezel of the light and the meter sensor with in an inch or so of 15m. Slight changes in distance can make a very marked difference in your reading on powerful lights. One foot off can throw your results off by 50k on some serious throwers. Obviously make sure to do the test in as dark of location as possibly and away from anything that might reflect extra light onto the sensor. Now turn the light on on start testing. Key there is not to record your initial readings. Most lights tend to have a power "flare" at start up and would thus give inflated results. I personally like to start paying attention to the readings after about 10 seconds. I prefer to move the light beam on and off multiple times, perhaps 5 seconds or so each time. This I have noticed helps to find the peak numbers. Doing this allows the beam to cross the sensor from edge to centerpoint many times. The reason this helps is that the hot point isn't always dead center of the spot. Now the number I record is the highest repeatable number once checking numbers after 10 seconds or so. Some people just fish around for the highest number without moving on and off the sensor - and thats just fine. Either method will do the trick. And some like to record "officially" after 30 seconds. Thats obviously fine and closer to ansi specs. I just personally like to go with highest repeatable test numbers during a test, again staying away from start up.
Now on a light like my TN31vn, it will get a test number of 2200 lux when I use the above test method at 15m. And to convert that number to get the proper lux number, simple multiply distance X distance X reading. So in this case, 15 X 15 X 2200 = 495,000. So my light is a 495k thrower. Now this formula works regardless of distance or type of light.
Just remember test distances need to be accurately measured and maintained. And make sure distances are adequate. Generally lights below 50k can be tested at exactly 1m, though longer distances is just fine and at times better. Lights in the 50k - 100k should be tested 5m or more. Lights over 100k should be tested at 10m or more if possible.

 

[880arm]

880arm,

Thanks for all the info.!!

Where I am NOT clear w/ any of these is for example when they say they can measure 50Klux what is the method[distance for measurement?] and can they measure a light accurately[or at all] that is 622Kcd?

No problem. Hope it helps.

The ratings you see for lights usually reflect a calculated (hypothetical) measure for intensity measured at 1m. However, most lights can't be accurately measured at 1m as that is too close to allow the beam to fully develop (collimate, converge, focus or whatever the proper term is). For a thrower this distance would likely be greater than it would for a really floody light. For what it's worth, the ANSI FL1 standard specifies the test distance to be 2, 10, or 30 meters (manufacturer's choice).

The light's intensity decreases greatly over distance which means your 600Klux light would be producing about 24Klux at a distance of only 5m, putting it within the range of most meters. This result is then plugged into the following formula to get the calculated intensity at 1m . . .

Measured intensity x (distance in meters)^2 = Peak beam intensity at 1m

​

Like rdfronty mentioned, it is important to accurately measure the distance and keep it consistent between tests. If you're just wanting to compare light A to light B then this doesn't really matter as you can just compare their measured results directly without having to back-calculate the 1m result.

 

[Capolini]

Thanks rdrfronty, 880arm and all others that posted.

Now I have to study all the info and then go from there!

 

[reppans]

Take an exposure reading with the camera. That is, look at how fast the shutter is going to be. Remember that you fixed the ISO and aperture, so the only thing left for the camera to calculate is shutter speed.

Take the reciprocal of the exposure. That is your foot candles. For example, if the exposure says 1/400 seconds, then the intensity of the light hitting your paper is 400 foot candles.

This method works well with a lightbox as a lumen meter too. For example, calibrate against a known 100 lumen light by playing with the ISO/aperture until exposure is zero'd at 1/100th of a second. Then fix ISO/aperture, and re-meter shutter speed for any other light or mode and your lumen answer will be the reciprocal of the shutter speed, including sub-lumen which will be seconds of exposure.

 

[TEEJ]

One thing I noticed when I migrated from testing lighting levels for night shooting ranges, emergency exits, etc, to testing of flashlights....was that - for flashlights, I initially assumed that I would be taking 1 meter lux levels to get cd...and, as some lights had ~ 100 k cd of throw, I'd need a meter with a center range (Center of a meter's range is typically where its most accurate) that included 100,000 lux.

In practice though, throw performance grew by leaps and bounds, and, I noticed the throwers were best measured MUCH FARTHER AWAY.

That essentially lead to seeing that as the primary POINT of measuring the cd was to get a REPRESENTATIVE measurement that could be then EXTRAPOLATED to predict the lux at various longer ranges....the best measurements were a LOT farther away, and, therefore, at lower lux levels.

So, the farther away the lux is measured at, the more representative the measurement will be of lux at longer ranges.

The other thing I noticed is that I could really use sub-lumen measurements to actually measure the light's throw at full distance ranges, and measure the periphery of flood, etc.

That allowed experimentation to "See what could be seen" at various low lighting levels, at various distances.


That lead to interesting observations, such as with some strong throwers, I could shine the light at a buddy holding a book 500 meters away, and not SEE my buddy at all, let alone the book, but HE could READ THE BOOK by the light from the flashlight, as 500 M away: It was bright enough, for him to read by, but, not for me to SEE him.

That meant that the lighting levels historically associated with emergency lighting, etc, a dim light that would allow you to not bump into stuff/moonlight, etc...became progressively less useful as the area you needed to see became farther away. That lead to understanding why, later when ANSI came out with their latest standards, that the 0.25 lux target was OK close up,and useless at long range.

And so forth.


So, a meter with good sub-lumen ability kills two birds with one stone, as, it means you can take measurements at really long distances, and, those measurements will tend to be the MOST representative.

 

[Capolini]

TEEJ


So, a meter with good sub-lumen ability kills two birds with one stone, as, it means you can take measurements at really long distances, and, those measurements will tend to be the MOST representative.

______________________________________________________________
Would the Extech EA30 fall in this category?

 

[degarb]

I don't recall where I bought my lux meter. Sub $40, I recall. It was a guilty purchase, since I thought it wouldn't make me money. Over the years, it reads surprisingly consistent from test to test (though you do need to "fish" around any hotspot/area to find the sweet spot).

However, I found that I could standardize my lighting technique, instantly quantify (always reinforcing eye perception) my lights. Great for communicating the effectiveness of a method to other people without showing them math.

My phone's lux meter seems to have a less of a dynamic range: too high lux reading in low light, and too low in high light conditions. Its numbers don't seem to correlate with my eye's opinion, like the dedicated lux meter.