Integrating sphere #3 (portable and overly stuffed with features)

I think that match did the same as you do but he wrote it up the wrong way around.

The ‘obscure method’ takes a careful performance to do it accurate, but a drawback is that to get the correct number, it is essential that your luxmeter is correctly calibrated, if the luxmeter is off, the multiplier will be off. Your current method does not care about the calibration of your luxmeter, the calibration comes from the reference flashlights.

I’m interested in the coating stuff from Sphereoptics, my own DIY BaSO4 coatings did not have that high reflectivivty that this stuff claims. The website does not mention a price or retailer. If you are able to obtain it, would you mind letting me know where, how and how much?

Ya, I will report back once I hear from them. If I don’t get a response via email soon I will try to reach out to one of our German speaking members and see if they will give em a call…

We may be out of lux on that premix even if they do contact me back. I just found this on another site $500-$1200?
http://www.labspherestore.com/SearchResults.asp?Search=6080&Search.x=8&Search.y=15

I am thinking if that is the case I may try to make some. Here is where I found out that it was made from.

PVA is not that expensive, and Bariumsulfate is not that expensive, so I guess they just tack on an extra $450 buck for adding the word “Labsphere”

Maybe, thanks for finding that abstract. I have some BaSO4 leftover and just ordered some PVA. Experiments are to come :slight_smile:

Teamwork makes the dream work. :+1:

‘obscure’ ?? (my finger hovering over the ‘RUDE’ button :wink: )
I would rather call my method ‘scientific’. It uses one fundamental formula:
LUMENS = LUX x AREA[m2] and is valid for a uniform bunch of light.

Never mind, I will issue a WARNING that this method cannot be used for a styrofoam ball because light will leak through besides the hole during the procedure and offset the calibration.
The wall has to be solid (metal in my project).
For styrofoam balls I think the best way is the ‘statistical’ way (guesswork with ‘known’ lights).

Put your styrofoam ball in a cardboard box with a hole and off you go :slight_smile:

Sometimes the most scientific method is not the most practical one, in this case for most people the accuracy is totally dependent on the least accurate measuring device on the planet:the dubiously calibrated chinese luxmeter. But if your luxmeter has a trusty calibration the method is really useful.

btw djozz, did you eventually get your CCT measuring device ( I guess you went after a i1Display Pro). And if so, I would like to know the price and the vendor, please. :+1:

Perhaps I should have bought an i1Display Pro…

Instead I have bougnt a very simple device, a homebrand product from Lumitronics named ColorSense. I hoped that it would work straight out of the box, but while playing with it, the reading went all over the place, could not get a grip on it. So I gave up on it for the moment. A thing to try is placing a white diffusor in front of the sensor, like luxmeters have. So I will have to make a little project of it.

http://www.leds.de/LED-Zubehoer/Steuerungstechnik/ColorSense.html

I’m with ya. I’ve got nothin’ but love for your project sixty :blush: I wasn’t meaning to imply that what you were doing was unscientific. I just got a little freaked out when I saw that post by match and then yours. I was like, “have I really been doing wrong for all these years??”

I made a video log on my build of one of the lumen tubes and on my old measuring setup last week. DIY lumen measuring device. Integrating shpere, and lumen tube.
I thought it might interest some people who want to build a cheap easy setup who are not as concerned with the level of precision discussed here. However I did want to make sure I wasn’t just spreading grotesque misinformation before posting, hence my badgering in this thread. Any misinformation in this vid will be mildly odorous at worst :student:

@vestureofblood:
No offence taken! I did’nt really consider using the new button :wink:
Great video of yours btw!
(fyi footcandles and lux are related by a factor just as inches/centimeters).

That’s what I found too, using a PublicLab spectrometer to try to measure color temperature and CRI. I could probably get it to a usable state with some effort and experimentation, but so far it hasn’t been very useful at all.

It’s at least good enough to confirm that color LEDs are the color they’re supposed to be, but that’s easy enough just by looking. For example:

Mind having a look at this at tell me what you think? Open Source DIY Spectrometer $45

If I stick with this “Hobby” for a longer stint than last time, I’ve considered buying this…Lighting Passport Smart Spectrometer. I’ve seen them listed for as little as $1295, a bargain for all they do. Measures CCT CRI CQS Illuminance Foot Candle CIE 1931 CIE 1976 Spectrum Diagram C78.377-2008 IEC-SDCM λp. The bluetooth connection is pretty sweet, and I think they would work well in our DIY integrating spheres.

-Michael

Should have read further before I hit reply to djozz’s post, sorry TK.

I referenced that same spectrometer above, what’s your opinion of it after using it?

-Michael

I think it has potential, but getting it to work well is nowhere near as simple as the site would suggest. When I’ve tried to measure flashlights with it, the readings go all over the place, making dramatic changes in response to very small changes in angle or positioning. The software for it is also pretty limited, so if you want to actually do CRI or CCT measurements you’ll probably have to write the tools yourself.

So far it’s kind of a neat toy, but not really a useful tool unless you put a lot of effort into it.

I hope the software has gotten better, but I haven’t looked in at least a year. They have released a new version of the hardware kit, at least, which looks like it might work a bit better, and provided better instructions on building it.

Sorry to hear that!
The instrument I made during my time at Philips also had problems with repeatability. The team that made the separate measuring head (with suction cup) started with placing the three sensors at an angle so that they pointed at the same pixels on the CRT screen to measure but they soon found out that a rotation of the head gave a different result. Eventually they ended up using a piece of milky, acrylic plastic in front of the sensors, just as you have in mind. The calibration took care of the slight miscoloring from the plastic. I hope that a piece of plastic will solve it for you.

I should probably try that too. :slight_smile:

I had been thinking of trying to attach a really white piece of paper or something at a 45 degree angle and bounce light in, but it’d be physically a lot easier to just stick a translucent sheet of something on the front of the measurement device.

Ok, thanks for the honest evaluation!

Guess its time to start trying to convince myself I could actually get a decent ROI on the Passport.

Thanks Again,
Michael

I have some stuff packed away somewhere that might work well. It’s a diffusion filter used in iPhone touchscreen/LCDs. Helps to equally disperse the light from the 4 or 5 LED’s mounted on the perimeter. Works really well at diffusion, will turn almost any light, even those with fairly tight beam, into more of a mule style beam pattern, all spread.

If you think that might help I’ll try to dig through my packed away stuff at storage and find you some.

-Michael

Ok, I bought a bottle of PVA (it is sold as a mould release agent for polyester and epoxy) and did a first experiment: I made a mixture of 20ml PVA and 15 grams of BaSO4, which appeared a good thickness to apply with a brush (about the thickness of latex wall paint), and applied two layers on a flat test-piece of styrofoam, drying the first layer in the sun before applying the second layer.

Observations:
-it applies really easy in a thick layer, much better than the BaSO4-latexpaint mixture that I used before. The second layer applies well too without disturbing the first layer.
-the result feels very durable, it does not scratch off at all with my finger nails.
-it is even somewhat flexible, does not crack when the styrofoam is bended a little.
-the two layers do not let much light through: compared to the bare styrofoam (2cm thick), the light through the styrofoam+2layers is reduced by 80-90% (estimation by eye).
-the coating looks really matt, like you want it to be for an integrating sphere coating.
-for an actual integrating sphere coating I would use 3 layers, also to get a smooth finish.
-a very rough first estimate is that when applied like I did, for a 30cm inner diameter styrofoam sphere, you need about 500gram BaSO4 and 650ml PVA.

I have not measured the big questions yet: if this coating improves the reflectivity of a sphere (my former latexpaint/BaSO4 coating even reduced reflectivity compared to bare styrofoam), I have to test that in an actual sphere, but when shining a flashlight at various angles suggests that reflectivity may just improve a bit.

So far so good! :slight_smile: