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LED
(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.
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but were superseded by lower-power LCDs within a few years.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 LEDs can provide
the backlight for LCD screens. See LCD.
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 |
| 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 |
| 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 |
| 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 |
| 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 |
| 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) |
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