A so-called grey body is a body for which the spectral emissivity is independent of wavelength, so that the total emissivity, ε ε , is a constant. In the more general (and realistic) case, the spectral emissivity depends on wavelength. The total emissivity, as applicable to the Stefan–Boltzmann law, may be calculated as a weighted average of the spectral emissivity, with the blackbody emission spectrum serving as the weighting function. It follows that if the spectral emissivity depends on wavelength then the total emissivity depends on the temperature, i.e., ε ε = ε ε ( T ) . However, if the dependence on wavelength is small, then the dependence on temperature will be small as well.