How are lumens measured

Maybe someone already asked this, here goes

When you have two torches of similar rating yet they vary in overall brightness (as much as 50%) then I have wondered how lumens really are measured, is it at quite a close distance because the real measure of a torch is how effective it is at say 1, 5 or 10 metres (IMHO).

My rule of thumb is to go outside after dark and shine two torches up into the sky and compare the result, this gives me a lot of info about how bright they really are.

In this case:
X-Glow ALC-0713D is probably about half as bright as Ray-Bow XS-9509 even though they have similar lumen ratings (around 150) and are of similar design and construction.

Lumens measure total luminous flux (human perception adjusted total light output), not luminous intensity (luminous flux per unit of solid angle, measured by candela). The only way to measure lumen output accurately is an integrating sphere. It is very, very difficult to impossible to even grossly compare lumen output by eye. What you are comparing by eye is candela.

Quite expensive...not even sure where you can get one. Many have made their own...see here

Lego995743 said:

where can you get an integrating sphere?

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