Light-Emitting Diode (LED), device that emits visible light or infrared radiation when an electric current passes through it (see Diode; Electromagnetic Radiation). LEDs are made of semiconductors, or electrical conductors, mixed with phosphors, substances that absorb electromagnetic radiation and reemit it as visible light (see Luminescence). When electrical current passes through the diode the semiconductor emits infrared radiation, which the phosphors in the diode absorb and reemit as visible light. The visible emission is useful for indicator lamps and alphanumeric displays in various electronic devices and appliances. Devices such as remote controls and cameras that focus automatically use infrared LEDs, which emit infrared radiation instead of visible light.
Light-emitting diodes use the properties of electroluminescence, in which certain substances emit electromagnetic radiation when excited by the flow of an electric current, and fluorescence, in which some substances absorb wavelengths of electromagnetic radiation other than visible light and reemit the radiation as visible light. When charged particles such as electrons pass through certain semiconductors, they boost to higher orbits one or more electrons in some of the atoms in the semiconductor. When these electrons fall back to lower orbits, the atom emits infrared radiation. When this radiation strikes a phosphor atom, electrons in the phosphor atom jump to higher orbits. The phosphor atom emits visible light when the electrons fall back to a lower orbit.
LEDs are made of a combination of elements from column III of the periodic table, such as aluminum, gallium, and indium, and column V of the periodic table, such as phosphorus, arsenic, and antimony. LEDs are made of semiconductors called III-V compound semiconductors. By changing the elements that compose the semiconductor and the ratio of column III elements to column V elements, LED manufacturers change the characteristics of the LED, including color, amount of visible versus infrared radiation, and brightness.
The organic light-emitting diode (OLED) is made of carbon-based polymers that use green, red, and blue fluorescent and phosphorescent dyes to produce a brilliant white light when connected to a source of electricity. Research reported in 2006 suggested a breakthrough in OLED technology in which an OLED device could be 100 percent efficient—that is, all of the electricity could be converted to light without giving off heat as incandescent lamps do. The breakthrough could have a significant impact on energy conservation. About 22 percent of the electricity used in buildings in the United States is used for lighting, and of that, 40 percent is consumed by energy-inefficient incandescent lamps.
Izvor Microsoft ® Encarta ® 2007.
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