I’m not too familiar with the Zebralight/cpfselfbuilt lumen scale.
DB Custom, Robo819, Richard at MTN and Tom E use the Manxbuggy1’s lumen tubes which I think are only 10% to 15% higher than Maukka’s readings. (certain throwy lights might be a bit higher due to no diffusers in the design)
Texas_Ace’s personal lumen tube did read a bit higher than the ones above. About 30% higher than Maukka’s. After getting some reference lights shipped to Maukka to test, he has adjusted his tube down to match. All of the Texas_Ace Lumen Tubes he sold have also been adjusted down to match. Officially he still states about a plus or minus 7% range on them.
Maukka has also decided to sell a small batch of carefully measured and documented lights for anyone who wishes to calibrate their own integrating sphere/lumen tube.
I think the bottom line is if you want exact lumen numbers your gonna have to buy a $10,000 professional integrating sphere.
If you don’t want to spend that much money, you can ship a certain light to be tested by someone who does have one. This is slow and can get very expensive the more lights that need to be sent.
The next cheapest method is to just build your own device then calibrate it with a certified light from someone like Maukka.
The cheapest and probably best way is to just buy a Texas_Ace Lumen tube. It’s already calibrated plus is very well thought out. Plus you get lumen readings right off the lux meter with no math involved.
The two homemade options are always going to have bigger tolerances, but they are much more practical and cheaper.