Improving the DIY integrating sphere

saabluster

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Saabluster,

Thanks for spending your time to do these tests. Do you still have the two small pieces of foam set up with your meter mounted to try one more test? Could you scuff the surface of another piece of foam with sandpaper so it takes some of the sheen off the surface of the foam, then test to see if that makes much difference? Try a fine grit paper.

Sure I can do that. I'll also try the test I already did but with a little bit more accuracy as to the angle between the two lights instead of just guessing the angle I am holding it at.
 

MrGman

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what is the brand name and model number of the light meter you are using? I would add a UV light into the mix. If the meter has the proper photopic filter in it, it should not read the UV light. There may be a very tiny amount of blue light that it does read, but if it reads higher readings than an actual blue LED than you know something is wrong. As I mentioned previously, I had one meter that did that (actually read higher than the green LED I was using) and sent it back for credit.
 

saabluster

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what is the brand name and model number of the light meter you are using? I would add a UV light into the mix. If the meter has the proper photopic filter in it, it should not read the UV light. There may be a very tiny amount of blue light that it does read, but if it reads higher readings than an actual blue LED than you know something is wrong. As I mentioned previously, I had one meter that did that (actually read higher than the green LED I was using) and sent it back for credit.
It is the Extech 407026. I tested it with a UV light already and it barely reads it at all.
 

MrGman

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Thanks for the info. I cannot trust a "Heavy" duty "Light" meter. That's just too much of a contradiction. :rolleyes: It would be nice to know how it does the changes for different color temperature lights. Normally you need 3 different color sensors to know what the color of the light is or a true spectral radiometer.
 
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saabluster

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Thanks for the info. I cannot trust a "Heavy" duty "Light" meter. That's just too much of a contradiction. :rolleyes: It would be nice to know how it does the changes for different color temperature lights. Normally you need 3 different color sensors to know what the color of the light is or a true spectral radiometer.

The reason they call it heavy-duty is because it comes with a removable hefty rubber cover to protect the meter. It is made for professionals not hobby work. So no contradiction there.
 

saabluster

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Saabluster,

Thanks for spending your time to do these tests. Do you still have the two small pieces of foam set up with your meter mounted to try one more test? Could you scuff the surface of another piece of foam with sandpaper so it takes some of the sheen off the surface of the foam, then test to see if that makes much difference? Try a fine grit paper.

OK so I finally got around to doing the test with the sandpaper. It did indeed have a very good effect. Here's the numbers.

--------------------90°(perpendicular) 20°
Bare unsanded foam__ 9 ____________ 123
Foam coated in BS ___11 ____________ 16
Sanded foam ________11 ____________ 29

Pretty remarkable change and a very simple and effective way to improve the diffusing ability of the foam. It will not however change the fact that it is throwing off the spectrum some but it is hard at this point to say how much. BTW I used a 400 grit wetsanding sandpaper. I really wouldn't use a real heavy sandpaper on there as the rougher kinds may snag the surface.
 
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saabluster

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One more update on how well the BS performs vs sanded foam as it relates to spectrum. I bought a 4sevens quark RGB to use as a calibration tool since it has excellent regulation and would also make it easy to test how well different surfaces reflect at different wavelengths. I used the same pieces of foam I used in the first experiment and found no appreciable difference in how well the BS and bare foam reflected red, green, and blue.

I also sanded the foam a little heavier than before but it did not improve the diffusing ability of the bare foam. So at least in this area bare foam just cannot match the performance of the BS.
 

ti-force

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Saabluster,

Thanks again for your time spent testing. So, as far as wavelength reflectance is concerned, do certain colors penetrate Styrofoam more than others? You stated earlier in this thread that diffusion of light from different beam angles (spot vs flood) was the biggest problem with these homemade spheres, and as your testing shows, sanding the surface to reduce glare greatly improves the ability of bare Styrofoam to diffuse light. So how much light is lost through the Styrofoam, bs vs bare Styrofoam, and how much do you think this loss would impact the accuracy for measuring lumens of cool white led's in a sphere that has been calibrated with known output lights, all of which being cool white led's?

Thanks again.
 

Got Lumens?

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Saabluster,
:clap:Thank you for doing the testing.
I am wondering if You have done any tests comparing Dupont's Styrofoam to "Smoothfoam"?
Everthing I've read says that smoothfoam is, well, smoother than styrofoam with less cavitation. So my question is would smoothfoam make a better sphere than styrofoam?
Thanks
GL
 

Kinnza

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I actually linked the article about using BS to enhance reflectivity and achieve a lambertian reflection 6 years ago (http://www.candlepowerforums.com/vb/showthread.php?142034-BaSO4-latex-flat-white-paint-superreflective-mix,) but there was no interest then. Probably if I had posted later DIY IS with it...

Anyway, I post because Ive been working with BS for some time so I think sharing my experience on it would be helpful.

The article linked did a great job quantifying the amount of BS necessary to get a reflectance close to Spectralon and more than good enough for a DIY IS. But I experienced that when using recommended amounts of BS on typical latex white paint (30% by volume, 50% by weight, give or take), the mix was very dense, so the only way to apply it is by hand, and that way is very difficult to get a layer flat and uniform. I found very interesting the way used by Saabluster to apply the BS over the applied paint, although I think that way the mix probably have way less BS to get close to Spectralon. Anyway, surely is enough to get a lambertian reflection so the IS is more reliable independent of the beam angle of the light.

I was interested on building a more accurate IS yet, so I wanted to obtain a some millimeters thick layer with enough BS. Did it but the layer finish wasnt flat (overcame it by sanding) nor uniform. Tested with an spectroradiometer, it showed no attenuation of any wavelength along most of visible range (440 to 700nm), although it began to be noticeable below 440nm and significant at 430nm. Fortunately most white LEDs uses a royal blue LED peaking about 450nm which usually emits just about 2% of its emitted energy below 435nm so effect on Lm measurement is negligible (additionally, human sensibility below 435nm is very low, less than 20lm/optical Watt).

I tried for some time to find a paint with a low carbonate load, in order to get a less dense mix when adding the BS. I didnt found it but recently I discovered a patented paint technology, called Lumitec (By Azko Nobel, different brand on each country) which seems to use BS as main load instead of carbonates. Just a guess, as manufacturer dont offer any detail on composition (protected info), but the fact is absolute white achieves a minimum reflection of 92% and (maybe thick layer may be close to 99%) with a lambertian reflection. Ivent tried it yet, although I plan to do it on next DIY IS, trying first it alone and adding a layer mixed with BS if reflectivity is not enough. That way should allow to spray the paint and get a uniform and flat finish. For those just trying to improve the lambertian reflection of their DIY IS, that paint could be a good way of getting it.
 

ti-force

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Kinnza,

Thanks for your contribution to this thread. It's appreciated :thumbsup:. I understand what you guys are saying, but is there any way either you or saabluster could show the actual lumen or output loss in percentage from a bs coated sphere to a bare styrofoam sphere that has been sanded for light diffusion? From the info you guys have provided, the bare Styrofoam surface that has been sanded with no addition of bs should show a higher loss than the bs coated styrofoam, but is the loss greater or less with different wavelengths? If so, which wavelengths and how much light do white leds produce in that range? I know this is important or you guys wouldn't spend the amount of time you do researching and testing, but could you please show a percentage of error range for uncoated and sanded styrofoam, or possibly just your results with one sample with a white led?

Thanks again.
 

Kinnza

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I never tried styrofoam, but Ill get a piece and make some measurements. But in order to have some meaningful results, I would need to build a closed box of it. I take vacations this weekend, so until end of September I cant do it. I dont know if Saabluster have it right now.

I cant do absolute measurements with the equipment I have, but yes comparative measurements (how much loss happen on the styrofoam box, as it and then sanded, and the box with paint+BS). This way is easy to know if there is any spectral attenuation and have a decent idea of the lm loss, which is difficult to measure accurately: with the styrofoam, it is to expect to have a variation on the measurement depending of the angle of the light beam entering the sphere, so probably it varies depending on how you put the flashlight in the port and the own optic configuration (different values measured for same LED with different optics).

I think Saabluster was mostly concerned about the last issue, as it does difficult to compare measurements from different DIY integrating spheres, and not so much for the lm loss, as anyway you need to weight measurements for a coefficient. As far as the lm loss is always similar, it is not an excessive problem.

Ill make the comparison when I came back from holidays, but in the meanwhile, those that actually have a IS with styrofoam can check how many measured values vary when trying different angles and specially, when measuring same system (LED/battery/driver) on a different optic, specifically flood vs throw. That is the relevant thing to know, and seeing Saabluster's vid, surely you can check for yourself if a styrofoam IS is reliable, as it reflectance proved to vary a lot with angle. As the sanded styrofoam resulted in way lower difference, it could be good enough for using it, its just a matter of performing some tests to check if results are consistent and repeatable.

Anyway, applying a layer on paint and BS on the way Saabluster did is very easy and cheap while strongly enhance the lambertian reflectivity ideal in a IS. So why not using it?

I want to test too the paint I talked about, maybe it's yet a good candidate too, easier to get and apply. I mean easier because BS is not easy to source, and often, when you find it, purity is not stated. Purity of the BS is important, specially for the high reflectivity. Barite (or baritine) is a waste for some mining operations, and its 93-99% BS. So its very cheap (you pay mostly the transportation cost), but the impurities affect optical performance. While I got 1Kg (more than 2 pounds) for 1€, and 25Kg for 9€ (17 cent/pound) of barite, refined, optical grade BS is way more expensive and difficult to find. Anyway, impurities affect the reflectance, but little the lambertian behavior (the ability to diffuse light)
 

ti-force

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Kinnza,

Thanks again for taking the time to reply and share your knowledge. And no rush on the testing. I'm just grateful that you're willing to do it. I'm very interested in your findings.

You asked why not use paint and BS as saabluster did, and I could understand this if one were to apply this while in the process of building a sphere, but in my case I've already completed mine and spent hours calibrating it with lights that have a known lumen output. I sanded the inside of my sphere when I was building it, so if the largest problem is varying results due to beam angle differences, and if sanding the surface is nearly as good of a solution as applying paint and BS, then I would rather not spend hours more of my time for little to no improvement.

Also, if sanding the surface is an acceptable method vs paint with BS, it seems like it would be easier to simply sand the sphere during the build process instead of having to purchase the paint, then source and purchase the BS and spent more time applying it. If it's worth the extra time and money spent I'm all for it, but if not I'd rather simply keep what I have.

Thanks again, and have a great vacation. Too bad I can't go with you :).
 
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Tom H

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Re: Improving the DIY integrating sphere -- Barium sulfate vs. flat white paint

One issue that I have not seen addressed here is how much is gained by going from flat white paint to the barium sulfate coating. My own experience with barium sulfate matches what others have mentioned; it is quite difficult to get a smooth even coating of the barium sulfate.

I did not address the angle vs. reflectivity parameters of the coatings, but only the reflection efficiency in terms of readings on the lux meter using the same sources after different coating experiments on an IS made of plaster of paris. Here is some of what I found: The lux readings increased by a factor of 2.6 going from unpainted plaster of paris to a surface painted with flat finish interior latex paint. Coating the surface with barium sulfate by the sprinkle wet paint with powder method decreased the lux readings for white LEDs by 8-10%, and the reading decreased by 31% for a red laser.
 

precisionworks

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I did some tests with laser pointers and I was surprised how uniformly lit was the inside of the sphere. So if the styrofoam is diffuse enough for a laser it should be diffuse enough for flashlights.

sphere6.jpg


My IS uses a 12" hollow styrene sphere, uncoated. Wooden sides protect the sphere (above) but it started like this:

sphere1.jpg


A correctly coated IS will certainly register readings closer to a laboratory IS, and this might be important if a number of people were trying to replicate readings from an identical light source. But most users don't have an IS for that purpose, rather they only want to know if light A is brighter than light B and by how much. For me it is a way to measure relative outputs of different lights. Surprisingly the numbers are close to those generated by a calibrated lab sphere.
 

Papa Bear

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I actually linked the article about using BS to enhance reflectivity and achieve a lambertian reflection 6 years ago (http://www.candlepowerforums.com/vb/showthread.php?142034-BaSO4-latex-flat-white-paint-superreflective-mix,) but there was no interest then. Probably if I had posted later DIY IS with it...

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Snip
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I tried for some time to find a paint with a low carbonate load, in order to get a less dense mix when adding the BS. I didnt found it but recently I discovered a patented paint technology, called Lumitec (By Azko Nobel, different brand on each country) which seems to use BS as main load instead of carbonates. Just a guess, as manufacturer dont offer any detail on composition (protected info), but the fact is absolute white achieves a minimum reflection of 92% and (maybe thick layer may be close to 99%) with a lambertian reflection. Ivent tried it yet, although I plan to do it on next DIY IS, trying first it alone and adding a layer mixed with BS if reflectivity is not enough. That way should allow to spray the paint and get a uniform and flat finish. For those just trying to improve the lambertian reflection of their DIY IS, that paint could be a good way of getting it.

The name of the company is actually spelled Akzo Nobel. In the US, the brand is Glidden Pro. The specific formulation is Diamond 450. The tint is Titanium White. I would post the link, but I am new to CPF and I got branded as a "spammer" the last time I did that :-(.

Just look up Glidden Professional and find the closest dealer.

I'll post a link later (after I am out of probation) to a review that a guy on AVS did. He was comparing 4 different paints he used to make movie screens.

I have also found a relatively cheap source for hollow foam balls (Link when I am out of probation).
 

Papa Bear

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I'm out of probation!!!

Here is the link for the AVS Forum post (teaser quote below):

The first number is cd/m2 with the sensor adjusted for maximum reading. The second number is cd/m2 with the meter lowered about 25 - 30 degrees. the third fourth and fifth numbers are the RGB values. The last number is deltaE from perfect neutral. A deltaE of less than 1.0 is considered perfect. Less than 3.0 is considered to be so close as to be indistinguishable from neutral by the human eye, at least according to what I've read.


Glidden Diamond 450 Titanium White:
36.35 31.6 245,246,243 1.43

Sherwin-Williams ProClassic Smooth Enamel Satin Extra White:
31.25 29.5 240,241,236 2.58

Carrada Brilliant White 1.4 Gain:
36.1 30.8 242,242,236 3.22

Behr 1850 UPW:
35.3 32.05 249,249,246 1.95

The Glidden Professional dealer locator is at this link.

16 in outer diameter styrene balls with 7/8 thick walls are available for $35.60 + $6.95 shipping here. They also have 24" and 30" OD balls, but I suspect the shipping costs are much higher (you have to call them for more information).
 

abuck

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hey guys,

could you share with us how you are mounting the led to the sphere? I'm on my way to build my own and i'm just not sure how to mount the led to the sphere...

anyway, pictures would be appreciated!
 

vestureofblood

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Hi all,

When you guys do your lumen testing in the spheres do you prefer to use the foot candle setting or the lux setting, and why?
 
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