LED

LEDs show an immunity to electromagnetic interference, power surge hazards, and changes in temperature. Red LEDs are sturdy, bright enough without being too hot, and cheap enough to be conveniently used in place of more common white light sources. Green ones are used to light up phone keypads, for instance. As circuit board indicators on personal computers, they can withstand the heat stress of active integrated circuitry. LEDs also show up on electronic newscasters, are used on a large scale on building exteriors but are also available in portable forms. Laptop computers use LEDs to create the equivalent of a 12-inch monitor on a much smaller scale. Long distance phone service is renewed at switchers and loop circuits, and cable TV transmissions are aided at relay stations with a combination of lasers and LEDs known as optical coupling. LEDs provide the stimulated emission of radiation required for onset of laser action in these fiber-optics applications. AT&T/Bell Labs has produced the basic LEDs for full-color reproduction-red, green and blue (RGB)-from the same material. An array of LED-supported colored lasers might produce a new kind of television set in the future.