I expect that most paint pigments affect more than one region of the visible spectrum so that it is impossible to create a combination that produces a tailormade absorption spectrum. It is probably why good luxmeters are so expensive: it takes exotic materials to produce a filter with an exact absorption spectrum.
Texas_Ace BLF Calibrated Lumen tube / Sphere No math skills needed - Several spheres still available
I was going to say basically the same. While a good idea on paper I have a feeling it would be quite difficult to make it work in practice and would net you other oddities. Such as I foresee different tint lights having the lumen skewed due to the paint absorbing more from one LED then another.
Putting us right back in the situation of having to round the number up or down to account for it.
Don’t get me wrong, it is a good idea and would be cool to test but we are talking dozens of hours of testing with some expensive equipment that most of us do not have at the minimum. That is a lot of time for what amounts to an almost unnoticeable to the human eye change.
Fair enough. 
I started a new thread about using the Texas_Ace Lumen tube to post measurements in reply to BLF member requests for specific flashlights.
Here:
Thanks to T_A and all who put in so much work making the “Tube” a thing.
All the Best,
Jeff
If this is already being done some place. Let me know and I’ll edit my POSTs to fix it.
Spamming is not allowed in this forum.
This is not spam, I just recommend what I think is good seller
You signed up to this forum and your very first post was a bunch of links to this company?
How did you even find this topic? It is 6 months old. Are you a flashlight person or did you just search online for people talking about PVC pipe? You realize this looks highly suspicious, right? This is the exact same behavior that a lot of spammers use. I just want you to be aware of that.
JasonWW, just go to one of the links and on top of the page click on "about" the company. That company's name looks very similar to the poster's.
Coincidence?
I am going to start building my own rudimentary lumen tube based on ideas from this and Matt smith , and others.
I was hoping to find out what material was used for the diffuser sheet in the junctions of Texas Ace’s version? Or what could be used in place of his diffuser sheets if the material he used is difficult to source?
Thank you in advance
Technically you can use a lot of diffusing sheets but the readings might not be as consistent. This is ok if you know to adjust for it but was not good enough for me to sell to others naturally.
The sheets I used were from a local shop, I think that they were used as lighting covers but I could not find the same thing at home depot. I tried a few of the ones I did find at home depot/lowes first but they did not diffuse the light enough and that led to inconsistent readings between floody and throwy lights.
You might get lucky and have a better selection at your local store though as I only had 1 option from home depot and another from lowes when I was testing (looked like they had places for more but were out of stock).
All that said, cutting these sheets without a laser cutter will be a real pain, they shatter with most cutting methods I tried so it is real hard to make them seal, they can still work but be prepared for some hassle.
Another option might be to use some DC fix film and apply it to some form of plexiglass, assuming you can get a circle cut out of it.
There is no way I would of tried to make these without access to a laser cutter that is for sure.
TA - thank you for this info! As i got halfway through reading your response i had the thought “what about dc fix on 1/8” plexiglass?” LOL, so i’m glad you mentioned that. That is probably what i will try for multiple reasons -
1. I do not have access to laser cutting or if i do it is too much legwork. unless i absolutely have to, in the event dc fix doesn’t work well enough.
2. I can cut plexiglass with my bandsaw (keeping the wrapper on it or cover it in painters tape to avoid scratching it on the saw’s table).
I had just assumed it was some diffuser material you had someone specifically engineer for the measurements of the tube. If that is not the case, and it doesn’t sound like it is, it seems that whatever gives the most consistent results is the best option. I feel dc fix and plexiglass will work fine for my needs.
Next question (since i have your attention lol) - Do you know where i can find calibrated lights like Maukka was selling?
Yeah, since you will be calibrating the whole sphere as a unit, the exact diffusing sheet you use is not super important as long as it does the job and does not cause anymore tint shift in the light then necessary. Most important thing is the calibration step.
DC fix should work fine, you will just have to play with how many layers to use. I ended up using 3 layers of the diffusion sheet I had to find I would not get any noticeable difference in readings when using different reflectors with the same LED. A sphere is better for this of course but a lot bulkier and expensive.
Maukka is the only source for calibrated lights that I know of, if he has some they are highly recommended.
Thanks TA!
Some types of the inflatable air pillow material used for filling voids in boxes when shipping packages is just slightly opaque / diffuse. This stuff is sold in rolls. Stack layer on layer to get just the right amount of blockage to fine tune the calibration to read 1:1. This may work best at the sensor side.
I used this method to calibrate a different lux meter for use with my TA tube and got it to read 1:1 to a Maukka light.
You might take a look at the photography world for diffusion material. You can find stuff that is uber consistent and easy to cut.
This stuff for instance. I got it from BH photovideo. Kind of expensive compared to the hardware store goodies. But so easy to work with.
, 
And when TA says it took months to get the first calibration - believe it!
When I did my version, when I finally got in the ballpark, well the heavens opened and angelic choirs began to sing…
My version.
Want one? Get it from TA unless you like to fuss (and fuss (and fuss)) with stuff.
Important tip, if you do this - record every change, no matter how small, or you will go nuts trying to get repeatable results.
All the Best,
Jeff
Wow, Hoop and Jeff thank you for this info. Jeff - that thing looks like it belongs in Marty’s workshop in back to the future lol. I dont think i am capable of doing that setup, i mean i cant even understand your notes! boy… I may need to. They make it look so easy online. If i am not trying to go for a 1:1 with the calibrations lights, and im OK using a formula and with about 90% accuracy (to start), i wonder if i can just use some of the Photography diffusion stuff. I dont want to spend months doing it…
Oh, also, TA or anyone else - do you sand down the sheen of the inside? or paint it? or treat it with anything? or does the diffusion film help alleviate the need for that?
Thanks!
And even then, the meter will still have a +–10% deviation unless you spend hunderds of dollars for a professional calibrated meter.
As said, every change will impact the reading, even inserting a larger or smaller light affects the reading.
So the real question is, how accurate you want your readings to be?
Question 2 is how large you want your setup to be?
Question 3 is how much effort you want to spend for your readings?
Etc. Etc…
If the diffusing sheets do their job and you spread them out over the length of the tube, there should not be any need for sanding the insides. This is part of why I hunted for the perfect diffusion material so long to save a ton of work on each sphere.
Even without that extra work I still get flashbacks to the weeks we spent building these spheres way back, learning as we went. Tubes all over the house in various states of completeness. Calibrations seeming to change just because someone else was testing it. Good times lol. Luckily I figured out most of the issues and got them consistent enough for our uses after a LOT of trial and error.
Without a proper sphere the real key was diffusing the light repeatedly, this removed most of the variance from light to light and made things much more consistent.
After that it was getting a proper calibration light to base the calibration off of. My home grown setup was WAY off and I had to send everyone some correction discs to fix it once I got Maukkas lights to do a real calibration.
Wow, thank you for sharing this hard won experience openly with us, and me! I bet it was a nightmare I. A way getting those setup properly in the beginning. This also makes me realize I really need to try and get the calibrated lights from Maukka …
I have always tried to be transparent about what I do and how I did it, at most waiting to release the full details until after I sold out of whatever it was I made.
My philosophy has always been that if someone wants to put the work in to do it themselves, more power to them, they are also the kind of people that would not consider paying for it pre-made from someone like me anyways. And if they did they would not be happy about it. So might as well help them out whenever possible.
I never want to be someone that forces people to buy something from me. I will build or DIY most things before even considering buying it pre-made, it would be wrong for me to not grant others that same choice.
The TA drives being a good example, I naturally could of kept those closed source and only available from me but instead I decided to release them publicly for those that wanted to DIY it and offered some for sale pre-made from me. Making them the most used modded light drivers ever as far as I know even years after I stopping making them.
That said one thing I have learned over the years is that sometimes, it is better to just buy something pre-made and be done with it unless the journey is something I want to experience lol.