How to 转换 luminous flux in lumens (lm) to luminous intensity in candela (cd).
You can 计算 but not 转换 lumens to candela, since candela and lumens do not represent the same quantity.
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 apex angle θ in degrees (°):
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 (°):
Iv(cd) = Φv(lm) / ( 2π(1 - cos(θ/2)) )
So
candela = lumens / ( 2π(1 - cos(degrees/2)) )
Or
cd = lm / ( 2π(1 - cos(°/2)) )
Find the luminous intensity Iv in candela (cd) when the luminous flux Φv in lumens (lm) is 337lm and the apex angle is 60°:
Iv(cd) = 337 lm / ( 2π(1 - cos(60°/2)) ) = 400.3 cd
