Lumens (lm) to candela (cd) calculator and how to calculate.

Enter the luminous flux in lumens, apex angle in degrees and press the *Calculate* button to get the luminous intensity in candela:

For uniform, isotropic light source, the luminous intensity *I*_{v} in candela (cd) is equal to the luminous flux Φ_{v} in lumens (lm),

divided by the solid angle *Ω* in steradians (sr):

*I*_{v(cd)} = *Φ*_{v(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 *I*_{v} in candela (cd) is equal to the luminous flux Φ_{v} in lumens (lm),

divided by 2 times pi times 1 minus cosine of half the apex angle *θ* in degrees (º):

*I*_{v(cd)} = *Φ*_{v(lm)} / ( 2π(1 - cos(*θ*/2)) )

So

candela = lumens / ( 2π(1 - cos(degrees/2)) )

Or

cd = lm / ( 2π(1 - cos(º/2)) )

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