In the study of heat transfer, 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.
Mathematical definitions Hemispherical absorptance Hemispherical absorptance of a surface, denoted is defined as
where is the radiant flux absorbed by that surface; is the radiant flux received by that surface.
Spectral hemispherical absorptance Spectral hemispherical absorptance in frequency and spectral hemispherical absorptance in wavelength of a surface, denoted and respectively, are defined as
where is the spectral radiant flux in frequency absorbed by that surface; is the spectral radiant flux in frequency received by that surface; is the spectral radiant flux in wavelength absorbed by that surface; is the spectral radiant flux in wavelength received by that surface.
Directional absorptance Directional absorptance of a surface, denoted , is defined as
where is the radiance absorbed by that surface; is the radiance received by that surface.
Spectral directional absorptance Spectral directional absorptance in frequency and spectral directional absorptance in wavelength of a surface, denoted and respectively, are defined as
where is the spectral radiance in frequency absorbed by that surface; is the spectral radiance received by that surface; is the spectral radiance in wavelength absorbed by that surface; is the spectral radiance in wavelength received by that surface.
Other radiometric coefficients
References