An
electric light is a device that produces light by the flow of electric current.
It is the most common form of artificial lighting and is essential to modern
society, providing interior lighting for buildings and exterior light for
evening and nighttime activities. Most electric lighting is powered by
centrally generated electric power, but lighting may also be powered by mobile
or standby electric generators or battery systems. Battery-powered lights,
usually called "flashlights" or "torches", are used for
portability and as backups when the main lights fail. The two main families of
electric light are incandescent lamps, which produce light by a filament heated
white-hot by electric current, and gas-discharge lamps, which produce light by
an electric arc through a gas. The energy efficiency of electric lighting has
increased radically since the first demonstration of arc lamps and the
incandescent light bulb of the 19th century. Modern electric light sources come
in a profusion of types and sizes adapted to a myriad of applications.
The most efficient source of electric light is the low-pressure sodium lamp. It produces, for all practical purposes, a monochromatic orange/yellow light, which gives a similarly monochromatic perceprtion of any illuminated scene. For this reason, it is generally reserved for outdoor public lighting usages. Low-pressure sodium lights are favoured for public lighting by astronomers, since the light pollution that they generate can be easily filtered, contrary to broadband or continuous spectra.
A discharge lamp has a glass or silica envelope containing two metal electrodes separated by a gas. Gases used include, neon, argon, xenon, sodium, metal halide, and mercury
With some discharge lamps, very high voltage is used to strike the arc. This requires an electrical circuit called an igniter, which is part of the ballast circuitry. After the arc is struck, the internal resistance of the lamp drops to a low level, and the ballast limits the current to the operating current. Without a ballast, excess current would flow, causing rapid destruction of the lamp.
The most efficient source of electric light is the low-pressure sodium lamp. It produces, for all practical purposes, a monochromatic orange/yellow light, which gives a similarly monochromatic perceprtion of any illuminated scene. For this reason, it is generally reserved for outdoor public lighting usages. Low-pressure sodium lights are favoured for public lighting by astronomers, since the light pollution that they generate can be easily filtered, contrary to broadband or continuous spectra.
A discharge lamp has a glass or silica envelope containing two metal electrodes separated by a gas. Gases used include, neon, argon, xenon, sodium, metal halide, and mercury
With some discharge lamps, very high voltage is used to strike the arc. This requires an electrical circuit called an igniter, which is part of the ballast circuitry. After the arc is struck, the internal resistance of the lamp drops to a low level, and the ballast limits the current to the operating current. Without a ballast, excess current would flow, causing rapid destruction of the lamp.
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