- Electric light
Most of the industrialized world is lit by electric lights, which are used both at night and to provide additional
lightduring the daytime. These lights are normally powered by the electric grid, but some run on local generators, and emergency generators serve as backups in hospitals and other locations where a loss of power could be catastrophic. Battery-powered lights, usually called " flashlights" or "torches", are used for portability and as backups when the main lights fail.
Types of electric lighting include:
incandescent light bulbs
gas discharge lamps, e.g., fluorescent lights and Compact fluorescent lamps, neon lamps, flood lamps, modern photographic flashes
light-emitting diodes, including OLEDs
Different types of lights have vastly differing efficiencies. [http://www.parliament.the-stationery-office.co.uk/pa/cm200203/cmselect/cmsctech/747/747we81.htm]
*Color temperature is defined as the temperature of a
black bodyemitting a similar spectrum; these spectra are quite different from those of black bodies.
The most efficient source of electric light is the low-pressure sodium lamp. It produces an almost
monochromaticorange light, which severely distorts color perception. 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 pollutionthat they generate can be easily filtered, contrary to broadband or continuous spectra.
The total amount of artificial light (especially from
street light) is sufficient for cities to be easily visible at night from the air, and from space. This wasted light is the source of light pollutionthat burdens astronomers and others.
Human-made lights highlight particularly developed or populated areas of the Earth's surface, including the seaboards of Europe, the eastern United States, and Japan.
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