(Light Emitting Diode) A display and lighting technology used in almost every electrical and electronic product on the market, from a tiny on/off light to digital readouts, flashlights, traffic lights and perimeter lighting. LEDs are also used as the light source in multimode fibers, optical mice and laser-class printers. See LED lightbulb.|
LEDs Vs. LCDs
In the early 1970s, red LEDs were used in the first digital watches, but were superseded by lower-power LCDs within a few years. LEDs still use more power than LCDs, but less power than incandescent bulbs. They also last for decades and are virtually indestructible.
LEDs and LCDs coexist on countless devices where the LEDs provide the status lights, and the LCDs display data. In addition, white or red, green and blue LEDs are used as the backlight source on many LCD TV sets. See LCD, LED TV and flat panel TV.
LEDs are semiconductor diodes that typically emit a single wavelength of light when charged with electricity. Originally red, today, several colors can be generated based on the material used for the tips of the probes. Aluminum indium gallium phosphide (AlInGaP) is used for red and yellow. Indium gallium nitride (InGaN) is used for green and blue, and with the addition of phosphor, for white light as well. See OLED, IRED, LED printer, fiber optics glossary and Nixie tube.
The LED is the semiconductor die itself, which sits in a reflective cup that acts as a heat sink and reflector. When voltage is applied to the LED, electrons and holes in the two semiconductor layers are attracted to each other at the junction. When they combine, they create photons.
LEDs and liquid crystal displays (LCDs) are widely used in combination as in this printer control panel. Alphanumeric readouts can be LED or LCD, but the billions of on/off indicators found on countless products such as this green Ready light are LEDs.
This Synchronar 2100 was the first solar powered watch. It also has the distinction of being the first LED watch. Models were already working prior to the announcement of Hamilton's famous Pulsar LED watch in 1970. (Image courtesy of the private collection of Peter Wenzig.)
LEDs provide much more flexibility than ordinary lights; witness this Los Angeles bedroom with illumination by Color Kinetics. With a flick of a switch, you can change the ambience. (Image courtesy of Color Kinetics, Inc.; Design and photo by Steven Cordrey)
This staircase in the Westin Hotel in Shanghai is illuminated by LEDs from Color Kinetics. It can cycle through a rainbow of colors or become a light show synchronized with music. (Image courtesy of Color Kinetics, Inc.; Design by Light Directions Hong Kong; Photo by Friendly Light)