Thanks Jeff for sharing your experiences. 
For a long time I felt alone working on the tubes. Trial and error and a never give up approach can give someone a heart attack.
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In the 8” tube, my Diffusers are rattle can sprayed with Matte White, 4 coats on the top Diffuser, 2 coats on the one 6” below it. They are 2 inside glued in place with no leakage around the edge. Using all the data on the MT09R, it was possible to adjust the tube to that light. An additional Diffuser is required for throwers. Both thrower and flooder lights have a slightly different number for calculations. I’m guessing about +/- 500 lumens at 6000 to 30,000 lumens, best I could do guessing.
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The 6” x 4” tube was more difficult than the 8” to tune, worked on it for the better part of a year, off and on. Same problem you stated about getting close to 1.0 then .760, then 1.192. Not to mention light meter additional calculations. I used ‘maukka’ Calibrated Light set on this tube. Give up a while, then back at it. Not sure it was worth the trouble after checking and documenting the few lights I have, LOL. 
Texas_Ace BLF Calibrated Lumen tube / Sphere No math skills needed - Several spheres still available
lol, no worries no offense taken. More felt bad you had to struggle through that alone, it is never fun doing that from scratch.
Yeah, people would ask a lot at first how accturate these tubes would be and kept being surprised when I would say not to treat them as an accurate lumen reading and more use them to compare readings between lights and between others with the same style tube.
All my tubes should be pretty comparable as they were all calibrated to within a ~2-3% of each other. That will grow over time though as things are moved around etc.
Yeah, I can build another 3.5”, PM me and we can go over the details if you want to go that way.
I have used this stuff to control brightness in the setup I use for run-times.
The thin white closed cell foam used to package some of our lights or other electronics works also.
The semi-transparent frosted plastic from gallon milk jugs (and the like) can be used as well.
And the best part is they are free. But don’t expect consistency from different sources of the material or even across a sheet of it.
Stuff designed to be used as a diffusion material is better choice if you want to go that route.
The biggest hurdle I had was getting the setup to work with throwers and floodies. Other than getting the readings close to some sane value…
Getting the beam diffused early and lining the tubes to prevent escape prone photons did it for me.
I suspect there are many ways to approach the build. Just have at it - and keep repeating:
It’s only a hobby - It’s only a hobby…
All the Best,
Jeff
But before you know it, you’re deep into it and it will drive you crazy sometimes.
I’ve had days i only could think of it and how to improve it.
I found out a white sheet of cotton cloth between the elbows works well, also used dicarded jugs as you mentioned.
When you have a reference light you don’t even need exact lumen readout, just correct it with the reference number to get the correct Lm output.
Yes, returning is no problem :+1:
So I’m building a Lumen tube and man oh man I never thought it’s such a chore just to get the parts! I had to go to two big name hardware chains just to get the parts, and mostly they were sold out. Seems there’s a plastics shortage according to the sales guy. I ended up with this…
4 inch to 3 inch 90-deg. closet elbow
Two 3 inch street 90’s
3 inch end cap for the luxmeter sensor. However the cap DOESN’T fit into the flange end of the street 90 (sold out of those) so I had to sand flush the end of the flange and cap and glued them together with white acrylic adhesive caulk.
This all cost me $30. When I checked 2 years ago to make it with 4 inch parts, it was $20. If I went with 4 inch, it was almost $50. Covid strikes again…
I’m interested in one please
Hi,
Also interested in acquiring one, 3,5” please with international shipping
Just wanted to let everyone know, someone wanted several of these tubes so I ordered some of the parts but they ended up changing their mind (had legit reasons).
So I am left with a bunch of parts taking up room (and could use the money to be frank).
If anyone wants one (or you know someone that does) let me know and I can build several mores tubes. Can do both 3.5” and 4.5”. Prices would be the same as the OP.
Well that’s very annoying. If you were to make more in the future I’d recommend charging a non refundable deposit for the cost of the parts.
I’ll share this around and see if there’s interest. I wish someone would make me a sphere, but the shipping to NZ wouldn’t be cheap
He had something unavoidable come up that caused him to cancel, I do not blame him at all, I would of done the same thing. I would of refunded any deposit under the circumstances anyways lol.
Mostly trying to clean some stuff up and tax time just hit me harder then expected, so could use some extra cash.
I’ll take one!
How often does it need to be recalibrated? Is there data logging capability with the meter?
Basically never IF you don’t change anything. I purchased calibration lights from maukka and it was only out by 4 ish lumens from memory.
You’d need to purchase another meter for data logging or just use a phone app like me
You can use a phone, but if you can swing roughly $100 to $150 for a used data logger, get that. Much easier to use and if you get a calibrated one it will be more accurate.
Make sure you calibrate it with lights with honest factory ratings (Nightwatch, thrunite, Olight, Rovyvon, Fenix, Speras are pretty trustworthy).
I’m interested in the 3.5”. Can you tell me if the 3.5 version work with the Noctigon K1? The head measures 2.84”.
Affirmative, it’ll fit up to 89mm, but you’ll need to make your own discs. I just use cardboard and reflective tape
Excellent, thanks. I’ll PM TexasAce.
Actually, the largest disc is 76mm, so you won’t need to make one for the K1 at only 72mm.