Emittance

The capacity of a material to emit radiant energy. The ratio of the radiant flux emitted by a physical surface to that emitted by a blackbody at the same temperature and under the same conditions. It can be expressed as 1-(long-wave infrared absorptance) for materials that are not transparent in the long-wave infrared spectrum. Emittance is a surface property; values range from 0.05 for brightly polished metals to 0.96 for flat black paint. The emittance for most materials is 0.9.