Luminescence is the generic term used for the emission of light which is not an effect of high temperature. So luminescence can be determined as an appearance of cold body radiation. This radiation can either be part of a chemical reaction or a result of subatomic motions or stress on a crystal. Another way to generate emission is incandescence where light is emitted by a substance as the result of heat. Luminescence is an umbrella term for those kinds of events where light emission is not the result of high temperatures. Luminescence is obtained under variety of excitation sources. The wavelength of emitted light is characteristic of the luminescent substance and not of the incident radiation.