Absorptance


Absorptance of the surface of a material is its effectiveness in absorbing radiant energy. It is the ratio of the absorbed to the incident radiant power. This should not be confused with absorbance and absorption coefficient.

Mathematical definitions

Hemispherical absorptance

Hemispherical absorptance of a surface, denoted A, is defined as
where
Spectral hemispherical absorptance in frequency and spectral hemispherical absorptance in wavelength of a surface, denoted Aν and Aλ respectively, are defined as
where
Directional absorptance of a surface, denoted AΩ, is defined as
where
Spectral directional absorptance in frequency and spectral directional absorptance in wavelength of a surface, denoted Aν,Ω and Aλ,Ω respectively, are defined as
where