Light excited in a body by some form of electromagnetic radiation in the ultraviolet, visible, or infrared regions of the electromagnetic spectrum. See electroluminescence, LED, and luminescence.
Photoluminescence is a process in which a chemical compound absorbs a photon (electromagnetic radiation), thus transitioning to a higher electronic energy state, and then radiates a photon back out, returning to a lower energy state. The period between absorption and emission is typically extremely short, on the order of 10 nanoseconds. Under special circumstances, however, this period can be extended into minutes or hours.