Electric lights are a convenient and economic form of artificial lighting which provide increased comfort, safety and efficiency. 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 energy efficiency of electric lighting has increased radically since the first demonstration arc lamps and the incandescent light bulb of the the 19th century. Modern electric light sources come in a profusion of types and sizes adapted to a myriad of applications.
source:http://en.wikipedia.org/wiki/Electric_light
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