Texas_Ace BLF Calibrated Lumen tube / Sphere No math skills needed - Several spheres still available See if he has any left… If you want lumens.
If you want candela (throw), the meter above fits the bill well. But throw will only measure the hottest part of the hot spot, not the overall output.
A sphere will measure overall output by integrating all the light to the meter. (more fair for floody lights)
I measure “rings” with a yardstick on my “beamshot wall”. At 10’ it gives an idea what area it’ll cover in the real world. The oslon white flat gives a little 4” square, and a nice op-reflectored s2+ gives a nice big, soft hotspot bigger than the yardstick. But the diameter gives you the focus of the light, not brightness. This is more of a subjective measure of preference. I have measured lights with a larger ring that are way less powerful than others. Some with a smaller spot are way more powerful than others. It’s not really accurate to use your judgement to compare lights this way.
Be sure to measure what you want to measure. TBH there is either throw or lumens. Each has a very specific, measurable number that can be translated universally. Hot spot diameter, not so much, but you are on the right track.
I built a 17” “spherical” sphere to measure lights. Followed the “match’s mod” and tweaked a little. I have tubes, but wanted to fit the GT in the opening (sphere is a little more flexible on inlet diameter) and also be a little more orthodox in my methodology. The tubes are considerably more simple to construct and/or buy and do 99% of the same thing and with less math (multipliers and such).
edit: other two posts deleted, ??, but I use a dr. meter lx1330b in my sphere and a hs1010a for throw measured at a specific distance from the emitter. Both are decent meters under $50, but a sphere (or tube) is needed for lumen readings.