floating lumens! my integrating sphere project

Very impressive and ingenious , sir .

I am hoisting a beer in your honor !

I really want to do this, it seems like an awesome project, the only thing holding me back is my meter is to expensive (especially considering the additional $120 I just paid to have it calibrated) to take it apart and mount the sensor inside a sphere like is required.

Your work looks really good. That soldering is amazing too. Congrats, I imagine your pretty proud of it, I know I would be.

thanks for the replies, guys.

This was the fun part of the report, estimating the real performance (how precise it is and what calibration I should use) of this (or any other) integrating spheres I find really difficult, but I made a start with that, it will be in the second post.

I will be proud whenever I have exactly figured out the ins and outs of this thing, how precise it is, or how not precise.

Nice build. Any reason for using Oslon instead of regular CREE? Their binning is tighter?

Wonderful! I did a lot of research, but I never ended up doing a sphere. I liked this pdf file on the subject and I was going to use Anatase Ti02 and Varathane interior gloss diamond water based polyurethane. I decided it was just too much money, since I wanted a 24 inch sphere and the foam sphere was way out of the price range. BaSO4 is also a real good idea for a sphere.

Great to see you doing it and looking for all the results!

No particular reason at all. It is about as efficient as a xpg2, so the output was good, and this one was not going into a flashlight anyway, it is 5700K, too cool for my taste.

It is indeed a waste to disassemble a perfectly working and even calibrated luxmeter (I'm jealous btw), but that is not at all necessary, you can clamp the intact sensor to a sphere as well (it just occupies a bit more surface). In fact that is the way all others that made an IS have done it, as far as I have seen.

mineetje!

Thanks for the pdf-link, I had not seen that source. I like the abrasion set-up with the vacuumcleaner, actual science often looks like that . In the article they said that they did not use BaSO4 because it formed cracks in the paint, but the way I used it mixed with latex paint does not produce any cracking, the coating is even slightly flexible, it survives light deformations of the styrofoam.

24 inch is a nice size, and over here a 24 inch styrofoam sphere is not that expensive: 18 dollars. If you ever decide to go ahead with the sphere, please let BLF know (I'm sure you will :-) ).

This is such a nice project. And I am just envious of your dogged determination to make the best IS in a budget friendly style. Love it.

And thank you for the reflow porn. Would you believe me that I was feeling just as impatient when I was waiting for that final little wiggle/slide the emitter does when the solder melts in your video as I am when I do it myself. I don´t think flashlight pron is good for my heart! LOL

Such a nice project so far. Really looking forward to your findings regarding corrections and accuracy. Keep it up :-)

(Sorry, only makes scense if you have seen "Breaking Bad TV-series".)

Nice project! :)

Nice work as well as read. Thanks for sharing and all the best for the rest.

!!

[quote=Illuminaria]
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LOL, I was wondering already if anyone noticed that I stopped working on it. I still have to do some tests on it before I start using it but started doing other things. Thanks for trying to keep me on the job :-)

Light leaking through the wall of the sphere is not of much concern… your calibration constant for converting lux to lumens will take care of that. And the same goes for external light getting into the sphere. Just subtract the “LED off” reading from the “LED on” reading. Even less of a concern with your sphere-in-a-box that blocks external light.

In fact the Sphere-o-Many-Mysteries has a ultra-bright light testing mode where I mount the lux sensor to the outer wall of the sphere and use the styrofoam wall as a light filter. It can handle around 600,000 lumens that way. Normally the lux sensor (a Taos TCS3210 color sensor green channel) looks into the sphere through a 1/8” diameter hole in the sphere wall. The sphere wall can act as the baffle, but I do have a piece of white cardstock as a baffle. The sensor is mounted around 45 degrees from the light port.

I saw some tests that showed the just sanding the gloss off the inner surface of a styrofoam sphere performed pretty much as well as a barium coating.

Any updates? I really like seeing these projects. It's a kick in the butt for me to finally getting around to making one. I really should build one since I don't have a convenient space to measure throwers with my lux meters. I even went to the hardware store to buy the parts to build an integrating plumbing pipe, but they didn't have the parts that other folks here have been using. It looks like I can get 30cm styrofoam hollow spheres online though, so I'll go that way. That part is easy though. It's calibration that I'm not looking forward to.

I have precious little time for the hobby at the moment (writing posts is a bit easier than actual hobbying, I can only really work on things when the family has gone to bed and in the last couple of weeks I have been too tired to go hobbying late at night)

Concerning the integrating sphere, I'm still measuring/troubleshooting to get within the 1% accuracy that I aim for. The latest problem is that the output readings of the same flashlights and leds are slowly declining over the last couple of weeks. I already found out that it is not a battery problem of the luxmeter. Leftover is 1) declining reflectivity (yellowing?) of the coating on the inside of the sphere, which would be disastrous but I do not consider this likely, and 2) slowly peeling off of the piece of tape with the hole in it that I used to decrease the sensitivity of the sensor. So next step is to dismantle the IS and have a look at the piece of tape, I really hope that that is the problem because that makes for a relatively easy fix (not use tape but something that stays in place better).

By the way, if I would make another sphere I may not bother with a coating (just stick with careful sanding of the styrofoam inside of the sphere with fine grit paper to decrease direct reflections), the integrating properties and angle insensitivity of the sphere without coating appear to be ok already without one. Also I would perhaps start with a bigger ball, in my sphere I really need the adjustment light to compensate for the with every different flashlight varying reflectivity of the hole area of the sphere, but with a considerable bigger sphere (like: bigger than 50cm diameter), the effect of the hole may be more negligable.

Real calibration will still be a problem, also for me. The only way for me is measuring as many known lightsources as I can, and make a sort of 'average best conversion factor'. I already found that the ceiling bounce lumens that I collected for the several lights relative to each other do not exactly match with the integrating sphere readings, the reason may be that the ceiling bounce method is more or less sensitive to the detection angle of the luxmeter (in other words: the beam profile of the light source), in the IS the angle is obviously not supposed to matter.

Nice build! Can get barium sulphate on Ebay. I will try to use some if I make a sphere, though I’d like to see before and after figures.

Was the meter really overwhelmed at 200000 range without the duct tape?

I will post some before and after coating figures, worrying is that I actually measured a bit less after doing the coating. I like to think that is because before coating the reflection was less 'lambertian' and relatively much of the first reflected light reached the sensor (dream on, djozz), but unfortunately the easiest explanation is that the reflectivity of my coating is worse than that of the bare styrofoam :-( (but hopefully at least more equal across the wavelength spectrum)

Before the piece of tape the maximum measurable amount of light was about 720 lumens. I was able to do some awfully precise moonlight measurements before taping the sensor :-)

the various posts, the large variations on calibration methods and results is suspect. A common BLF calibration LED or source would help make the various lumen claims a more accurate.

A known common binned LED at an agreed exact voltage or using the port size method for an across the forum calibration method if you will.