Comparing LED flashlights using lumens

The meter is a good idea, but making an integrating sphere... is hard. I've seen 'em carved from solid MgO (by machining hemispherical cavities), because it's SO hard to trust the whiteness of finishes.

Well, that's mighty whit of ya.

On Jan 25, 2018, whit3rd wrote (in article):

We are overthinking this. I?ve built perfectly servicable integrating ?spheres? using a large cardboard box painted white inside with a painted cardboard diagonal baffle inside that blocked all direct optical paths from light source (a big xenon flash) to light meter (a Quantum flash meter). Flash and meter are on opposite sides of the baffle. The error over a true sphere is of order 0.1 stops (~7%), which is quite adequate for photographic purposes.

There is one thing to know - for ultraviolet emitters (like xenon flash tubes), don?t use outside paints, because many of them are fluorescent (so they will be whiter than white in the sun). Use at least two coats of some kind of interior flat white enamel. I used a rattle can paint, but brushing is better. Use BIN alcohol (not water) white primer first, or the cardboard will drink too much paint, and never dry. Joe Gwinn

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Oh, the fancy MgO integrating sphere was for Cerenkov radiation, that includes a fairly large spectrum (infrared on up), maybe for visible light some paints ARE white.

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I've heard of people making integrating sphere's from ping pong balls.

George H.