50cm is about 20 inches. So not huge. I’m sure it’s expensive, though. Plus he’s got all that spectral analysis equipment. I assumed he worked in a lab or something and used their equipment in his off time. 
Texas_Ace BLF Calibrated Lumen tube / Sphere No math skills needed - Several spheres still available
I heard those sphere cost about $10000…
My 4” light tube wasn’t that far off but I did have to make an adjustment, now its reading pretty much spot on to my stock Surefire and Malkoff lights with known out put. Tested 10 Surefire and 10 Malkoff’s all lights have Constant current drivers and the spec’s are easy enough to check online. The repeatability is amazing
A couple of examples… a Malkoff Hound Dog NW 1000 ansi lumens…
Malkoff Hound Dog CW 1100-1200 ansi lumens
All it took was a piece of Walmart white plastic bag stretched over the light meter :+1:
I tested a few of Randy Brogden’s PFlexPro lights that he tested… pretty much Spot On!
Yes, the repeatability was the key reason I spent 6 months perfecting this design. Without the diffusing sheets the numbers would vary by large amounts even with just a few mm of movement and throwers got a large advantage as well.
Glad to see with minor adjustments the results fall in line, I am thinking that the idea of putting something on the sensor end could be a fairly simple fix for everyone and would be possible for me to ship to everyone without a large expenditure on my end.
I will gladly pay to help defray what ever cost you may incur to deliver a fix that makes all the tubes more accurate and consistent with each other
I will most likely take you up on that. When I get to a point of having a fix figured out feel free to message me. It will most likely be a few weeks so I will have lost this post by then I am sure lol.
hi kiwi, can you tell us what adjustment do you make on your 4” tube ? Thanks.
What is the red indictator by the tube?? What does it do?
It’s his lighted mouse wheel
Thanks… kiwi is bitter !
He stretched a white plastic bag from a local store over the sensor. Very similar to what I did using some wax tissue paper.
I put brand new batteries in the Meter ( I have had low/crappy batteries give me High Lux readings before) and after many hours of trying different materials ……I tried the Walmart white plastic bag…. 1 layer stretched over meter shoved into the end of the tube 
Just curious, is the hole in the centering ring just perfectly sized for this light so only the very edge of the bezel is resting on it? (not blocking any of the reflector area)
I thought we had to hold the light through the hole, starting at roughly flush then move it up and down.
In most cases you have to hold it but some lights will rest on it. If you hold the ring up to the light you can see if it will block any of the reflector easily. If not then you can simply rest it on top of the ring.
It completely depends on the light you are using.
It is all pretty intuitive once you get it I think.
I see thanks for explaining.
How much smaller than the hole can the head of the light be without having too much light escaping around the open edges?
No it didn’t make any major difference, I tried all different scenario’s, light just thru the bigger cut out, a little lower, moved it around, nothing major a couple lumens, but if you go too low/too high then you see the lux drop like a rock… I even turned the centering rings over to the silver painted side and measured.
I’m not worried about 20-40 lumens I don’t build many pocket fondling EDC lights to care about it.
Your asking a ton of questions, but you should just wait until your tube arrives. It’s super difficult to put the answers into words. All your questions will be answered once you try it out.
It is one of those case by case basis type of deals. After you play with it you will see pretty quick the effects of using differnt sized rings or moving the light up or down.
As was said, pushing the light in too far or pulling it out too far can have big effects, the ring size is less important within reason.
You can make your own rings out of cardboard as well if you have an odd sized light. These are just some general sized rings that work with most lights.
Do you think lumen tube will melt if i test 15 minutes continually of flashlights that are 1000-17000 lumen ??