A student of mine has asked this question from looking at the photometric data of the Source4 19 degree.
published numbers are: candelas = 243520, Field angle = 19 degrees, field lumens = 11,180
however, if you use the standard formula for calculating lumens,
F = Iv × 2π × (1 - cos(A/2))
you get F = 243520 x 2π x (1 -cos (19/2)) = 20,984 lumens.
Well, I couldn't give a good answer so I'm asking here....ANYONE??
