Building an Integrating Sphere ...

[precisionworks]

I was able to remove the straight cut tube that points down from the sensor port (painted flat black inside) & replace it with a 45° angle cut tube painted flat white inside. The long point of the 45° cut faces the light port so that any spill will hit the point & be reflected. The opposite side of the tube is in the shadow of the 45° point, so no direct light can strike the inside of the tube. The reason for the flat white is to try to match the reflectance of the Styrofoam interior.





The output of the lights are still in the same order except that the U2 moves above the E1B. I played with the radius squared numbers and settled on 18 as being as close to published figures as possible. 18 = 4.24" radius, or about 8.5" internal sphere diameter. Best scientific guess is that the Styrofoam is not as bright as a commercial sphere, so my 10" is producing results like a commercial 8.5" sphere.

Latest (hopefully last) revision. Here are the readings. First reading is my lumen calculation, followed by factory stated lumens:

Mac's Custom P7 (AW C-cell LiIon) = 782 lumens (about 800 per Mac)

Malkoff M60 with 60Ω Sandwiche Shoppe mod = 15/192 lumens (235 per Malkoff website)

Surefire U2 = 7/114 lumens (2/100 per SF)

Surefire E1B = 11/113 lumens (5/80 per SF)

Novatac 120P = .23/11/99 lumens (.23/10/120 per NovaTac)

Muyshondt Aeon = 10/92 lumens (?/114 per Muyshondt site)

Muyshondt Nautilus = 6/91 lumens (?/107 per Brightguy site)

McGizmo LunaSol 20 = 9/73 lumens (9/78 per Don)

Surefire L4 = 66 lumens (100 per SF)

M60LL in Surefire G2 = 61 lumens (80 per Malkoff site)

Surefire E2L (single stage Cree) = 57 lumens (45 per SF)

McGizmo SunDrop = 46 lumens (40-50 per Don)

Surefire E1L (single stage Cree) = 40 lumens (30 per SF)

Muyshondt CR2 Ion = 3/29 lumens

Surefire KL1 (Luxeon) head = 29 lumens

Gerber Trio (2 AA Lithium) = 22 lumens (24 per Gerber)

 

[MrGman]

That is starting to look really good. I have just received my Malkoff M60, I will measure it at work first chance I get next week. I already have measured the M60F at a peak of 202 lumens. I have the SureFire 6P, I can put it in that and will again measure it in the Solarforce L2 with 1 extension and the 2X17500 batteries that seem to work so well. If you were going to get one of these or can borrow one that is another reference.

If you have or can get a Fenix T1/TK10 I have measured those new at 225 lumens. Solarforce R2 single mode at 200 lumens max, no less than 180 lumens depending on how its mounted.

the mag light LEDs for the 4 c/d cell with no head on it but just sticking the exposed LED into the sphere until I got a peak reading were no better than 50 lumens. This would be a good test because all of the light is coming out the side of the emitter's special lens, so if your sphere works well, it would collect all that light and integrate it to give you 50 lumens.

I applaud your diligent effort :twothumbs to make it as accurate as possible and good for total comparative efforts.

 

[precisionworks]

I applaud your diligent effort :twothumbs to make it as accurate as possible and good for total comparative efforts.

I appreciate you saying that. Your comments were my primary motivation to keep tweaking the design to get it as correct as possible.

Half-watt as caused me to test & retest the E1B ... it still gives readings that I consider extraordinary. But those readings are also supported by white wall shots & ceiling bounce meter readings - it is one bright light.

Using the correction or division factor of 18 produces lumen readings that closely correlate with most of the manufacturers stated outputs. I don't have any of the other lights you suggested testing, but I'll be happy to test any light that anyone sends, and I'll pay return shipping. I'd like to build as large a database as possible, but I currently have most every light that I want.

 

[MrGman]

Now that you have this data please put together this simple table of your measured Lumens readings versus the Vendor's stated Lumens. If its multimode list the mode (hi-med-low) on each individual line. Don't bother to list the lux readings as they are not useful in this quick comparison table. This will help to see how close your readings have come for those of us who are not familiar with some of those lights. As we build up the list of confirmed readings and the table grows longer we will see how good it is or if it needs further refinement.

But this really looks good. :thumbsup: :thumbsup:

I am very curious how it will track from the low level to the brighter lights and whether or not the Incans versus LEDs show any differences.

Since you have the 6P have you tried its normal incan light yet with good batteries? I think mine measured 50 lumens. Its another plot point to compare.

Even if you IS is not perfect, it will still be a much better total light measuring tool that will be effective for comparisons of various lights than other techniques. Readings from light to light, regardless of beam pattern should be more consistent for the various light types.

Now you should also consider building an exact duplicate and then testing that the readings are the same and figuring out the cost. Why you say? I am guessing that you will be able to sell it to one of these other guys who tests a boatload of flashlights and still have a boatload of flashlights available to test. If some one like Bessie Benny bought one and it was consistent and measured all those lights he had and got lumens readings to build a very large confirmed table set of readings, that would help everyone out.

You should give yourself a reasonable profit for your skills and labor that you put into it and don't let anyone make you feel bad about making an honest profit from your labor. You deserve it. :twothumbs

Of course if some of these guys are close to you they may want to come over and do a lot of testing with you and publish data out the wazoo.

Keep up the good work. G

 

[MrGman]

I measured the new Malkoff M60 in the IS at work today using the Surefire P6 bezel. It measured 220 lumens and dropped down to around 216 as it was warming up. I would use these numbers to calibrate the constant for your sphere. I talked to my PhD Optical Engineer coworker/friend today about your project. He did say that what ever the correction factor is, it would be a constant and work across the board. So if it winds up being 18 or 12 or XX we should get good readings using that constant for all readings of high and low power lights. Assuming for a moment that your Malkoff M60 is within 5% of what mine reads and I have a feeling it is if not within 2%, then I would take the lux readings off of that when it is dead center in the opening and just at the entrance, then divide by 216 and that should be your constant. I find that if I push the lights into the sphere the readings go down and if I pull them back away from the edge of the sphere the readings go down. tilting it doesn't have much effect which should be normal.

On a side note the M60F in the Solarforce deep crenalated bezel was down around 200 lumens. The bezel is blocking some of the light around the perimeter as it sticks out so far and the meter is sensing that small loss. So from now on all my pills will be read using the SureFire Bezel only.

I plan on sending you a Solarforce R2 5 mode pill to keep. I will take careful readings using 6 volts from 2 primaries as it doesn't like higher voltage, in the SureFire bezel, in high, med, and low mode. I will send you the readings and then send you the pill. Hang on to the pill as that will be your calibration reference unit when measured inside a SureFire Bezel with fresh primary batteries. May be a while before I can get this done, as I have some personal business to attend to but send me a PM with your mailing address if you want the pill.

If ever your readings start to drift, you can use the pill. If the time comes where we question the pill you can send it back and I can double check it and then send it back to you. Your lux meter may drift over time as they are all want to do.

Hows that for starters?

 

[precisionworks]

WOW!

I really appreciate all your effort. Work has kept me from replying to your first post, but I am also eager to get a 'calibration standard'. Industrial IS have a tungsten calibration light run from a constant voltage/constant current power supply.

whether or not the Incans versus LEDs show any differences.

I noticed that all the regulated LEDs stay at a near constant light meter reading. I did poke the 6P incan into the sphere & immediately noticed a reading that decreased a little bit every couple of seconds (non-regulated hotwire, I suppose). Each light meter does have an individual spectral response curve, so some meters will read some lights at a different value. My ExTech EA31 manual says "Calibrated to a standard incan lamp at a color temp of 2856K".

Assuming for a moment that your Malkoff M60 is within 5% of what mine reads

Readings are within 3% of each other:thumbsup: I think my 18 number is awfully close to correct.

 

[MrGman]

The filaments of an incandescent lamp give off infrared energy. As the heat builds up the visible light energy drops off a little bit ever so slowly on incans. So the lumens readings does come down, beside what battery voltage drop is going to do.

I spoke to Gene Malkoff a while back. He doesn't actually have the equipment to measure lumens but goes by what some of his customers and vendors give him data on.

The M60 and F series LEDs, I am sure are capable of more than 235 lumens from the emitter, but with the optics in front of them, regardless of type there will be some loss of peak lumens.

I measured a real diffuser that I was given and it was dropping the lumens down by 10%. The 6 degree optic is great but I am sure that the output is not at the original 235 lumens. My reading of 220 I believe is much closer to the truth. Especially when compared side by side to the Fenix T1 by eye and by the IS, the Fenix is just a touch brighter and its starts at 230 and drifts down to 225. As the phosphor warms up its efficiency does drop every so slightly. This will stabilize and if you are holding steady for a longer ready than the first 10 seconds its usually gone.

Point is I think it would be good for now to assume your M60 is the same brightness as mine and use 220 lumens out to find your more finely tuned constant "correction factor number" and go with that.

I saw that you updated your previous set of numbers and it looks good. That one SureFire E1B measuring 130 lumens and rated at 80 is the only puzzling one. Are one of those numbers a typo? If not its always possible that what ever the controller components are supposed to be doing for regulation, it was set wrong or has a faulty component that it is allowing it to drive harder than what they had intended. Otherwise I would say that your baffle just isn't quite big enough and your positioning of the light is such that this one is still causing direct spill onto the photo detector some how.

by tilting the light at the input port the brightness should not really go up or down to any significant value since in theory the sphere is still collecting it all. If you find that your readings do change substantially, then the baffle is not large enough or in the exact best spot.

Of course if all other flashlights are reading true to form once we have the final fine tuning "calibration" I would say ignore this one light and be glad to have it (as I think you already are).

So I will try and take some readings of the 5 mode unit next week and send it out to you (provided you remember to pm with an address, but no rush).

Also do you have the original incan lamp for the P6 to measure with a fresh set of primary batteries?

and lastly, isn't it better to have a good feel for what the total light output is in lumens rather than a lux reading of the hot spot?

Once you know what 100 lumens really is, its easier to understand that the new Malkoff 60 puts out 220 plus, or the Fenix T1 puts out 225 or that a small EDC light puts out 55 lumens and know what that really means??? :thumbsup:

This is really good. I would expect that some people will want you to measure their lights as the data is getting very close to what I would call trustworthy.

:goodjob:

 

[precisionworks]

That one SureFire E1B measuring 130 lumens and rated at 80 is the only puzzling one.

Same here, G. White wall shots, side by side, as well as metered ceiling bounce tests (4' to ceiling + 4' bounce back) show the E1B as brighter than the 120P, and almost the same as the U2. Other members have made similar comments in PMs to me. It is awfully bright ... I may send it to you to test in your sphere at work.

tilting the light at the input port the brightness should not really go up or down to any significant value

Tilting makes no difference on any light ... there is a 'sweet spot' in the light tube that generates a max reading. Normally it's before the bezel of the light reaches the end of the tube, which projects just slightly beyond the inside of the foam wall.

I'll PM my address:thumbsup:

 

[wbp]

Very interesting discussion, I've been wanting to do this for some time. I own a 6" Hoffman IS, but it has a reference light source installed and I am reluctant to remove it for fear of losing the calibration.

This looks to be the same sphere as you used:
http://www.plasteelcorp.com/mm5/merchant.mvc?Screen=PROD&Store_Code=PCO&Product_Code=10072

They also have 8" and other sizes.

William

 

[precisionworks]

Good call on the link to plasteelcorp, that is exactly the one. Probably made by one foam molder & distributed by a dozen retailers. The 12" size works well, I'd try a larger one except that the larger sizes quickly increase in price.

it has a reference light source installed and I am reluctant to remove it for fear of losing the calibration.

That sounds like the wise approach. I really would like to figure out a light source of known luminous flux, then build a regulated DC power supply to drive that bulb - probably what you have in your Hoffman. But the numbers generated in my IS do track closely (in most cases) with those from the manufacturers. IMO, this is a much better approach than a one meter reading of the hotspot, which tells only a small part of the total story.

 

[wbp]

That sounds like the wise approach. I really would like to figure out a light source of known luminous flux, then build a regulated DC power supply to drive that bulb - probably what you have in your Hoffman. But the numbers generated in my IS do track closely (in most cases) with those from the manufacturers. IMO, this is a much better approach than a one meter reading of the hotspot, which tells only a small part of the total story.

Most reference light sources are incandescent, running on very well regulated moderate/low voltage so as to reduce the effects of filament wear, and to get them to output Illuminant A ( (x,y)=(0.44758, 0.40745) - around 2856 K). The problem is that inexpensive light meters will read VERY differently at Illuminant A, which is what they were calibrated with, than they will at 5400K or 6500K.

So even if you calibrated your setup with an accurate incandescent light source, you would not get accurate readings from an LED flashlight with any of the Extech or similar meters. You'd be better off with an LED reference, which shouldn't be too hard to build. Or just use a known LED flashlight with a regulated power supply...

To get accurate measurements at different frequencies you have to spend a LOT more than the price the meter you are using, the most accurate being a spectroradiometer (I own two).

William

 

[precisionworks]

That's an interesting point ... I really thought than an incan reference light would be better, but it makes sense to use a LED reference when all my lights but two are LED.

My meter instructions came with a spectral response chart, and it showed that the greatest response is not at LED color temp, but rather at incan color temp. The area under the bell curve appears to be 500nm to 600 nm.

use a known LED flashlight with a regulated power supply...

That sounds like the best plan.

 

[MrGman]

All that really means for your set up is that you would have to use a different constant number to divide the lux by once you had a known reference when using incans versus LEDs.

They normally drive the filament with a constant current power supply where its ramped up to the desired value and held there to 3 digits behind the decimal point such as 1.000 amps. The current definitely changes with a constant voltage source as the filament gets hot and still drifts a little after it is hot. Can't hold constant current and constant voltage at the same time into the load. So constant current is best and let the voltage drop be whatever the load dictates. As long as you ramp it up slowly for things like a real filament its no problem. We have one in the optics lab for our reference light sources and the ones the engineers are testing. For instance we have a green LED array that is driven to 1.000 amps and makes 80 lumens. It is used to check the system whenver the engineer wants to or when it comes back from calibration each year. That is just one test sample they use.

But since most of your testing will be LEDs, an LED light source would be best. I didn't have time to get readings on the one I am going to send you today, maybe tomorrow or Monday.

 

[wbp]

They normally drive the filament with a constant current power supply where its ramped up to the desired value and held there to 3 digits behind the decimal point such as 1.000 amps. The current definitely changes with a constant voltage source as the filament gets hot and still drifts a little after it is hot. Can't hold constant current and constant voltage at the same time into the load. So constant current is best and let the voltage drop be whatever the load dictates. As long as you ramp it up slowly for things like a real filament its no problem.

Incandescent lamp reference sources that I am familiar with adjust voltage, not current. A good one includes use a calibrated sensor to measure the lamp's output. The voltage determines the color of the lamp's output. The illuminance is adjusted by opening or closing a variable width slit.

 

[wbp]

Now that I look at them more I think the spheres from Plasteel are different. Those are styrofoam, which is coarser, vs. polystyrene from Barnard. I've got one of each on order so we'll see.

Some of the variation in your readings are going to be from the frequency response of the Extech meter.

Precisionworks, where are you located? I might be able to help you calibrate your meter against a spectroradiometer...

William

 

[MrGman]

Before I lose the data I measured my Solarforce R2 5 mode pill inside a Surefire 6P host with 2 new Surefire batteries.

At high mode it came on at 160 lumens and settled in around 155 lumens.
in medium mode it came on at 87 and settled in to around 85 lumens.

in low mode it was 37 lumens. I will try and get it shipped to you tomorrow or next Monday, keep it as a reference.

 

[precisionworks]

where are you located? I might be able to help you calibrate your meter against a spectroradiometer...

That would be neat, William. I'll PM my address info, location is 89 miles southeast of St Louis.

I'm happy to see that you have two spheres ordered ... I wondered if/when someone else would try this. Eager to see the reflectance difference between the two materials.

If I did this again, a baffle or baffles would be installed prior to boxing in the sphere.

 

[Endeavour]

Precisionworks: A bit of food for thought from my end - you may want to consider applying a coating of some kind (thick primer, an epoxy resin like Envirotex swirled around the inside), followed by a coating of highly reflective white paint (www.labsphere.com has very lambertian coatings, others may sell some as well), which may give you a nicer optical surface inside the sphere, as opposed to raw styrofoam.

Certainly nice work so far, and a big :thumbsup: to your efforts in obtaining more accurate light readings in a DIY fashion rather than simply accepting the constraints of the norm.

-Enrique

 

[McGizmo]

I was told by one of the experts at one of the Sphere companies that in a pinch, the cheap Styrofoam coolers make a reasonably effective IS. In terms of materials, teflon seems to be a very good material for light reflectance and being easy to machine would probably be good for ports in an IS or as reducing collars in the port to keep the light "in".

Be sure to confirm compatibility of a foam with any adhesive or coating! :green: Anybody ever mix up a batch of polyester resin in a styrofoam coffee cup!? (don't do it!)

 

[MrGman]

The integration spheres I have looked into at work do not have "reflective" white paint or coatings on the inside. It is a soft, I want to say non gloss, or "flat" white. It gathers all the light but you don't want actual close to mirror like reflections because that will bounce the hotspot into the photodetector and give false high readings. I guess I am trying to say you don't want the interior surface to be shiny, from what I have seen it should not be. Other than that as white as white gets.