luminescence, general term applied to all forms of cool light, i.e., light emitted by sources other than a hot, incandescent body, such as a blackbody radiator. Luminescence is caused by the movement of electrons within a substance from more energetic states to less energetic states. There are many types of luminescence, including chemiluminescence, produced by certain chemical reactions, chiefly oxidations, at low temperatures; electroluminescence, produced by electric discharges, which may appear when silk or fur is stroked or when adhesive surfaces are separated; and triboluminescence, produced by rubbing or crushing crystals. Bioluminescence is luminescence produced by living organisms and is thought to be a type of chemiluminescence. The luminescence observed in the sea is produced by living organisms, many of them microscopic, that collect at the surface. Other examples of bioluminescence include glowworms, fireflies, and various fungi and bacteria found on rotting wood or decomposing flesh. If the luminescence is caused by absorption of some form of radiant energy, such as ultraviolet radiation or X rays (or by some other form of energy, such as mechanical pressure), and ceases as soon as (or very shortly after) the radiation causing it ceases, then it is known as fluorescence. If the luminescence continues after the radiation causing it has stopped, then it is known as phosphorescence. The term phosphorescence is often incorrectly considered synonymous with luminescence.

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