A light-emitting diode (LED) is a semiconductor device that produces light from electricity. LEDs last a long time and do not break easily (compared to incandescent lightbulbs). They can produce many different colors. They are efficient - most of the energy makes light, not heat.
An LED is a type of diode that makes one color of light when electricity is sent through it in the expected direction (electrically biased in the forward direction). This effect is a kind of electroluminescence.
The color of the light depends on the chemical composition of the semiconducting material used, and can be near-ultraviolet, visible or infrared. The color affects how much electricity is used by the LED. 
LEDs are used in many places. They are the green power lights on many electronic devices, they can be used to make bright advertising signs, brake lights on a car, and more recently, light bulbs for the home. LEDs bright enough to illuminate rooms are usually more expensive the regular lightbulbs.
LEDs, which make their own light, should not be confused with LCDs, which block light.
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