(Emissivity) 1 = εR + εT + εA, where εR is the energy reflected, ET is the energy transmitted through the material and EA is the energy absorbed by the material which is reemitted. The ability to reemit the energy is the emissivity. The common emissivity (ε) of a material is equal to 1– εR. This is an indicator of the property of a material to absorb radiation such as white light or infrared radiation and a perfect absorber of energy is a black body where ε = 1. (Driggers RC, Cox P, Edwards T (1998) Introduction to infrared and electro-optical systems. Artech House, Aylesford, UK, January; Handbook of infrared materials. Klocek P (ed). Marcel Dekker, New York, 1991).