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An electric light is a device that produces visible 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. Before electric lighting became common in the early 20th century, people used candles, gas lights, oil lamps, and fires.〔 The two main categories of electric lights are ''incandescent lamps'', which produce light by a filament heated white-hot by electric current, and ''gas-discharge lamps'', which produce light by means of an electric arc through a gas. Once the voltaic pile, created in 1800 by Alessandro Volta, became available as a power source, Humphry Davy developed the first incandescent light in 1802, followed by the first practical electric arc light in 1806. By the 1870s, Davy's arc lamp had been successfully commercialized, and was used to light many public spaces. The development of a steadily glowing filament suitable for interior lighting took longer, but by the early twentieth century Thomas Edison and others had successfully developed options, replacing the arc light with incandescents. 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. Most modern 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 word "lamp" can refer either to a light source or an or the appliance that holds the source. ==Types== Types of electric lighting include: *incandescent light bulbs *arc lamps *gas-discharge lamps, e.g., fluorescent lights and compact fluorescent lamps, neon lamps, flood lamps, modern photographic flashes *lasers *light-emitting diodes, including OLEDs *sulfur lamps Different types of lights have vastly differing efficiencies and color of light. () *Color temperature is defined as the temperature of a black body emitting 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, 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「electric light」の詳細全文を読む スポンサード リンク
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