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light-emitting diode (LED)
Semiconductor diode that produces visible or infrared light when subjected to an electric current, as a result of electroluminescence. Visible-light LEDs are used in many electronic devices as indicator lamps (e.g., an on/off indicator) and, when arranged in a matrix, to spell out letters or numbers on alphanumeric displays. Infrared LEDs are used in optoelectronics (e.g., in auto-focus cameras and television remote controls) and as light sources in some long-range fibre-optic communications systems. LEDs are formed by the so-called III-V compound semiconductors related to gallium arsenide. They consume little power and are long-lasting and inexpensive.
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In the early 1970s, red LEDs were used in the first digital watches, but were superseded by lower-power LCDs within a few years.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.
Several Colors
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.
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| An LED Unit |
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| 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. |
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| LED Vs. LCD |
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| 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. |
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| The First LED Watch |
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| 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.) |
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| Change the Mood |
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| 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) |
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| Rockin' Stairs |
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| 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) |
LED
| (electronics) | LED - Light-Emitting Diode. |
Led’
a river in Arkhangel’sk Oblast, RSFSR, a left tributary of the Vaga (Severnaia Dvina basin). Length, 184 km; basin area, 2,690 sq km. It originates from a lake, Letozero, and is very meandering. The Led’ is fed primarily by snow. The mean flow rate 42 km from the mouth is 16.7 cu m per sec. The Led’ freezes in late October or in November, thawing in late April or May. It is used for floating timber. Fish are abundant.
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