 Spectral radiosity in frequency of a "surface", denoted "J"e,ν, is defined as
where "ν" is the frequency.Spectral radiosity in wavelength of a "surface", denoted "J"e,λ, is defined as
where "λ" is the wavelength.The radiosity of an "opaque", gray and diffuse surface is given by
where

Normally, "E"e is the unknown variable and will depend on the surrounding surfaces.