Lumens (lm) to candela (cd) 计算器 and how to 计算.
输入 the luminous flux in lumens, apex angle in degrees and press the 计算 button to get the luminous intensity in candela:
For uniform, isotropic 光照 source, the luminous intensity Iv in candela (cd) is equal to the luminous flux Φv in lumens (lm),
divided by the solid angle Ω in steradians (sr):
Iv(cd) = Φv(lm) / Ω(sr)
The solid angle Ω in steradians (sr) is equal to 2 times pi times 1 minus cosine of half the cone apex angle θ in degrees (º):
Ω(sr) = 2π(1 - cos(θ/2))
The luminous intensity Iv in candela (cd) is equal to the luminous flux Φv in lumens (lm),
divided by 2 times pi times 1 minus cosine of half the apex angle θ in degrees (º):
Iv(cd) = Φv(lm) / ( 2π(1 - cos(θ/2)) )
So
candela = lumens / ( 2π(1 - cos(degrees/2)) )
Or
cd = lm / ( 2π(1 - cos(º/2)) )
