Radiance is defined by
where
the approximation holds for small A and Ω,
L is the radiance (W·m-2·sr-1),
Φ is the radiant flux or power (W),
θ is the angle between the surface normal and the specified direction,
A is the area of the source (m2), and
Ω is the solid angle (sr).
The spectral radiance (radiance per unit wavelength) is written Lλ and the radiance per unit freq ...
Luminance is defined by
where
L is the luminance (cd/m2),
F is the luminous flux or luminous power (lm),
θ is the angle between the surface normal and the specified direction,
A is the area of the source (m2), and
Ω is the solid angle (sr).
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