Originally Posted by cjwood555

The relationship between Lumens and Candelas depends on how the lense/reflector system works and how it was measured.

An isotropic (equal light in all directions) 1Mcd lamp would emit 4*pi*1M lumens = roughly 12M lumens.
An isotropic 4000 lumen lamp would emit 4000/(4pi) cd = roughly 333 cd.


However, torches are not isotropic. If they measure the brightness in a 2-degree hot spot then:

1Mcd * (2*pi*(1-cos(2degress/2))) = 1Mcd * ~0.001 = 956 lumens.

Whereas if the 4000 lumens torch were equivalently focused:

4000lm / (2*pi*(1-cos(2degrees/2))) = 4000lm / ~0.001 = 4.2Mcd