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general term applied to all forms of cool light, i.e., light emitted by
sources other than a hot, incandescent body, such as a black body
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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RachelWingfield - 09 Dec 2003
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