Spectral hemispherical transmittance in frequency and spectral hemispherical transmittance in wavelength of a surface, denoted T and T respectively, are defined as
where
*Φ is the spectral radiant flux in frequency transmitted by that surface;
*Φ is the spectral radiant flux in frequency received by that surface;
*Φ is the spectral radiant flux in wavelength transmitted by that surface;
*Φ is the spectral radiant flux in wavelength received by that surface.