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

I’ve found Zebralights make a good constant output source for calibration purposes, as long as they’re only on a medium setting and have reasonably full batteries. I’m using selfbuilt’s data to choose reference lights though, since he has such nice runtime output graphs.

Here’s a Zebralight on two medium modes:

TK,

That helps in ways you cant imagine. I’ve had a Zebralight sc52 since like last year. Mine is the XM-L version. I love the light because its AA and Type III HA natural. But I was never able to get anywhere near a factory rating on output with it. Worse still there was no change to the turbo mode even using a 14500. Max output was like 154 lumens. Seriously I thought it was broke until just now. When I saw that M2 thing, my hopes are what lit up. I picked mine up second had so it never occurred to me to look at the instructions. Fortunately the new version has the same UI… :slight_smile:

I keep my D40A as new, and solely for checking my multiplier, keep it in its holster so not to damage the anti-reflection coating (which would alter the OTF output), it only comes out when a reference source is needed. When using it, I keep the batteries more than half full, switch it to turbo (~900lm) for 10 seconds to warm the light up, then switch back to high (~550 lumen according to the manual) which is then very nicely constant (in my integrating sphere #II it measures the same everytime within 0.5%, which maintains my confidence in both my D40A and my integrating sphere :slight_smile: ) . My ‘djozz-lumen’ is based on this high setting of my D40A, assuming that the 550 lumen is correct. It is not really important for what I do that this is really 550 lumen or a bit off (although I want to have it really measured sometime), what is important to me that it is exactly the same output every time, so that all my light measurements can be compared to each other.

I’m nowhere near that careful. :stuck_out_tongue_winking_eye:

I’d like to be, but I haven’t been doing much where accurate consistent measurements are very important. So, take my ideas with a grain of salt. Djozz knows what he’s doing. :slight_smile:

Right now I am leaning toward djs 2 ball design. I am also considering doing a coat of barium sulfate on the inside. I noticed that pro grade sphere use this so I assume there must be some benefit. I found a place that sells it premixed in polyvinyl alcohol.

I am hoping it can be applied directly to the foam using a sprayer. Still waiting for them to contact me back.

Vestureofblood, you know I'm a big fan of yours. Is this a project you are going to possibly bring to life? If so I would like to know more about it. I'm assuming it will do large flashlights too?

Thanks jhalb. I would like to make a new setup. I have been using a pretty rough light box for years. The other day I made one of those lumen tubes just for fun, but am not all that impressed with it. I was thinking for the new sphere I will probly cut the hole for the size of a maglite head since I work with them a lot. I will keep the lumen tube for measuring larger lights as it was made from 4” pipe.

I have another question for the pros… What method are you guys using to derive your multiplier?

I have always done it like this.

1. Take know source ( in my case 875 lumen maglite measured by another member).
2. Divide lumen output by lux reading.

Example 875 lumen light produces 2550 lux. So 875 divided by 2550= 0.343

So from hence forth all measurements from other lights are multiplied by .343

However just now reading posts by others I see that Match appears to be doing the opposite.

A quote from his post.

but the most accurate one I tried was to simply take a light of known value, test it to get the lux reading, and then divide that reading by it’s alleged lumen rating.

Then here I looked and found yet an even more obscure method. Something about measuring the hole??

How are you doing it?

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