Secondary emission sources
Radiometry and non-coherent sources

A body's own, or thermal, emission is dictated only by its temperature and the absorption/emission factor of the material of which it is made. While this is the only source of radiation from a black body, it is, in many cases, only one of several contributions to the radiation from the objects around us. Indeed, for the majority of sources, the proportion of thermal emission in their overall radiation can be reduced by the phenomena of reflection, transmission or scattering of ambient illumination. In spectral ranges where the material's reflection and/or transmission factor is non-zero, any body is the source of so-called secondary radiation, since it reflects or transmits a fraction of the flux it receives from its environment.

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