I ask generally for lumen tubes what stock lights for cheapest money invested are best for calibrating a tube.
Zebralight or Fenix are too much expensive, the idea was if someone tested some cheaper light and know that exactly some number of lumens light have to recommend it.
No such light exists. No two lights put out exactly the same. Sorry.
If you are in the Europe area you can probably find an existing light of yours that has stable output and send it to Maukka to be measured in his sphere. If in the USA you can send it to Texas_Ace to be measured in his lumen tube. Then you will have your own reference light.
Since Cree has a 14% tolerance range for all of their LED’s, that is the minimum tolerance you will get for any light. This is why DIY spheres vary so widely.
I personally tested hundreds of lights in my sphere but never found one that I would recommend that someone uses to single handedly calibrate a sphere. Adding more lights should make things better but it is like adding more watches, it just makes you more confused when they don’t agree.
Not being able to measure low lumens in the tube is not a problem. Since lux and lumen are linear when the beam stays constant, just measure a higher mode in the tube and then measure the lux on the lowest and the one you did in the tube. The factor stays the same. Just clamp the light and meter so they don’t move at all between changing modes.
For example, in the tube you get 1000 lumens on the high mode. Then you take a normal lux reading from 50 cm (or close enough to have enough resolution on the low mode) and get 4000 lx on high and 40 lx on low. Therefore the lumen on low is 40/4000*1000=10 lm.
Good info!
I added the TA Lumen Tube info to my signature. Hopefully this will clear up any questions people might have on other threads about how I’m measuring lumens.
Maybe all owners of TA’s Tube could do this? We could be a little team. 
Yeep i’m in 
Tested my sphere with the new disks with an HDS, it was within 2 lumens which is good enough for me, kudos. I plan on testing some other beam shapes but I’m happy so far.
It’s pricey but HDS should be a perfect calibration light considering Henry claims he calibrates each light to the claimed output.
Great! Yes, it is looking like the HDS lights might indeed be a good calibration light, they seem to be lining up very close.
Nice description on that Lumen tube. I noticed you still list the tolerance as plus or minus 7%. Using the reference lights you got from Maukka aren’t you able to get the tolerances a little better?
I always under-rate things 
The highest deviance I actually saw from the stock spheres with disc installs was an outlier with just over 5% before I corrected it (with 2-3% being average).
If I ever make more of them I should indeed be able to get things closer.
For now though 7% gives a windows for any outliers in this batch that I was not able to recalibrate here and it lines up with the official Cree tolerance ratings.
As a side benefit it might help people realize that even these spheres are not accurate to a single digits.
All of that said, I could technically rate them at 5% and still be over-rating them on the ones I have here if I don’t include the spheres already in the wild. Just not sure if that is fair since they would all be compared equally. I can’t know for 100% sure there are no spheres I sold previously that fall outside 5% once the Correction discs are installed.
Cool. Thanks.
Has anyone with a TA Lumen tube measured a Rofis MR70?
I’ve seen a lot of varying tailcap amp draws so there’s not much consistency. I need to know what High actually is. It’s probably less than 1500, but I’m not sure how much less.
Thanks
Just FYI, maukka is now offering a calibrated light kit as well as light testing service.
Very nice, glad to see he is offering that. Worth every penny.
Ace are the larger tubes you make 4” or 4.5”? I see in the OP it says 4.5 but elsewhere I saw 4 mentioned. Either way can I buy a set of those diffuses and some of the white plastic rings?
TA, just out of curiosity… how much would the 3.5” tube cost without the lux meter?
I have the exact same meter already.
Tried my tube today, every light is about 20-40% off, they read way too low, wonder if I have a dodgy light meter.
They are 4” PVC but the opening is 4.5”, so kinda both.
I might have a few scrap diffusers left but pretty sure I used almost all the good ones, I would have to buy another sheet to cut out more. I suppose I could do this if you wanted enough of them.
I do have a few complete spheres left here.
It would be best to use the meter it comes with since that is what it was calibrated with.
Far as savings, I suppose I could knock off the $16 that the meter cost me from the price if you rally wanted to do it that way. Although the accuracy would be unknown at that point.