Gas discharge lamps are a family of artificial light sources that generate light by sending an
electrical discharge through an
ionized gas, i.e. a
plasma. The character of the gas discharge critically depends on the frequency or modulation of the current: see the entry on a
frequency classification of plasmas. Typically, such lamps use a
noble gas (
argon,
neon,
krypton and
xenon) or a mixture of these gases. Most lamps are filled with additional materials, like
mercury,
sodium, and/or
metal halides. In operation the gas is ionized, and free electrons, accelerated by the
electrical field in the tube, collide with gas and metal atoms. Some electrons circling around the gas and metal atoms are
excited by these collisions, bringing them to a higher energy state. When the electron falls back to its original state, it emits a
photon, resulting in visible light or
ultraviolet radiation. Ultraviolet radiation is converted to visible light by a
fluorescent coating on the inside of the lamp's glass surface for some lamp types. The
fluorescent lamp is perhaps the best known gas discharge lamp.
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