Phosphorescence is a type of LUMINESCENCE, which is the emission of light from a material without heat. It is distinct from fluorescence, which is the emission of light from a material when exposed to ultraviolet radiation. Phosphorescence is a type of GLOW that is caused by the absorption of energy from some other source, such as visible light or ultraviolet radiation. The light emitted by phosphorescence is usually of a lower intensity than that of fluorescence and can last for several minutes or even hours after the source of energy has been removed.