- A light-emitting
diode (LED) is a semiconductor diode that emits incoherent
narrow-spectrum light when electrically biased in the forward
direction of the p-n junction. This effect is a form of
- An LED is
usually a small area source, often with extra optics added to the chip
that shapes its radiation pattern. The color of the emitted light
depends on the composition and condition of the semi conducting
material used, and can be infrared, visible, or near-ultraviolet.
- LED lamps
(also called LED bars or Illuminators) come in different shapes, among
them the light bulb shape with a large Edison screw and MR16 shape with
a bi-pin base. Other models might have a small Edison fitting, (Bipin
cap) or (bayonet socket). This includes low voltage
varieties and replacements for regular AC mains (120-240VAC) lighting.
Currently the latter are less widely available but this is changing
- First, a
semiconductor wafer is made. The crystalline semiconductor is grown in
a high temperature, high pressure chamber. Gallium, arsenic, and/or
phosphor are purified and mixed together in the chamber. The heat and
pressure liquify and press the components together so that they are
forced into a solution.
- To keep
them from escaping into the pressurized gas in the chamber, they are
often covered with a layer of liquid boron oxide, which seals them off
so that they must "stick together." This is known as liquid
encapsulation, or the Czochralski crystal growth method. After
the elements are mixed in a uniform solution, a rod is dipped into the
solution and pulled out slowly.
- 2 The
boule is then sliced into very thin wafers of semiconductor,
approximately 10 mils thick, or about as thick as a garbage bag. The
wafers are polished until the surfaces are very smooth, so that they
will readily accept more layers of semiconductor on their surface. The
principle is similar to sanding a table before painting it. Each wafer
should be a single crystal of material of uniform composition.
Allied Vision Technologies’
booth at VISION 2007 can experience the future of digital machine
vision with the premiere of a brand new AVT camera family as well as
fun demos of new vision applications.
Organic Light Emitting Diode
technology and it promises to revolutionize almost everything that
uses displays from cell phones, PDAs and keyboards, to computer
monitors and HDTVs.
Breakthroughs in this field
have made available high intensity LEDs in Red, Green, Blue, and
Amber. These LEDs have made it possible to produce displays bright
enough for outdoor use with viewing angles that are equal to or better
than other technologies currently available.
Beyond 2005, the LED market
will expand at single-digit rates for a few years, predicts, while new
applications for ultra-high brightness (UHB) LEDs is partially offset
by reduced demand for high-brightness (HB) LEDs, and increased
competition with more suppliers for the HB market
The market for displays has
increased steadily during the Information Age. Its past growth was
closely linked to the personal-computer market, but now many other
types of electronic gadgets are requiring more sophisticated display
systems. As the pundits accurately predicted, PCs are no longer the
exclusive tools of scientists and engineers, and have taken their
place among other common household appliances. Some analysts forecast
that PC sales may not continue to grow at the current rate
Light-emitting diode (LED)
chip makers hope to make big inroads within the next decade into the
$12 billion conventional lighting market, now served by incandescent
and fluorescent bulbs. But in the meantime, they are doing very well
supplying lights for cell phones, autos and traffic signals.
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