Lumens (lm) to millicandela (mcd) 計算機 and how to 計算.
Enter the luminous flux in lumens, apex angle in degrees and press the 計算 button
to get the luminous intensity in millicandela:
For uniform, isotropic light source, the luminous intensity Iv in millicandela (mcd) is equal to 1000 times the luminous flux Φv in lumens (lm),
divided by the solid angle Ω in steradians (sr):
Iv(mcd) = 1000 × Φv(lm) / Ω(sr)
The solid angle Ω in steradians (sr) is equal to 2 times pi times 1 minus cosine of half the apex angle θ in degrees (°):
Ω(sr) = 2π(1 - cos(θ/2))
The luminous intensity Iv in millicandela (mcd) is equal to 1000 times the luminous flux Φv in lumens (lm),
divided by 2 times pi times 1 minus cosine of half the apex angle θ in degrees (°):
Iv(mcd) = 1000 × Φv(lm) / ( 2π(1 - cos(θ/2)) )
So
millicandela = 1000 × lumens / ( 2π(1 - cos(degrees/2)) )
Or
mcd = 1000 × lm / ( 2π(1 - cos(°/2)) )
