" If every American home replaced just one light bulb with one that has
earned the ENERGY STAR, we would save enough energy to light 2 million
homes for a year, save about $460 million in annual energy costs, and
prevent 6 billion pounds of greenhouse gas emissions per year,
equivalent to the emissions from about 550,000 cars "... www.energystar.gov
A Light Emitting Diode (LED) is a two-lead semiconductor light source. It is a basic pn-junction diode, which emits light when activated. When a suitable voltage is applied to the leads, electrons are able to recombine with electron holes within the device, releasing energy in the form of photons. This effect is called electroluminescence, and the color of the light (corresponding to the energy of the photon) is determined by the energy band gap of the semiconductor. An LED is often small in area (less than 1 mm2) and integrated optical components may be used to shape its radiation pattern.
Appearing as practical electronic components in 1962,[8]
the earliest LEDs emitted low-intensity infrared light. Infrared LEDs
are still frequently used as transmitting elements in remote-control
circuits, such as those in remote controls for a wide variety of
consumer electronics. The first visible-light LEDs were also of low
intensity, and limited to red. Modern LEDs are available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.
Early LEDs were often used as indicator lamps for electronic devices,
replacing small incandescent bulbs. They were soon packaged into
numeric readouts in the form of seven-segment displays, and were commonly seen in digital clocks. Recent developments in LEDs permit them to be used in environmental
and task lighting. LEDs have many advantages over incandescent light
sources including lower energy consumption, longer lifetime, improved
physical robustness, smaller size, and faster switching. Light-emitting
diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals,
and camera flashes. However, LEDs powerful enough for room lighting are
still relatively expensive, and require more precise current and heat
management than compact fluorescent lamp sources of comparable output.
LEDs have allowed new text, video displays, and sensors to be
developed, while their high switching rates are also useful in advanced
communications technology. On October 7, 2014, the Nobel Prize in Physics was awarded to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura
for "the invention of efficient blue light-emitting diodes which has
enabled bright and energy-saving white light sources" or, less formally,
LED lamps.
Text Source: WikiPedia
A normal light bulb is made
up of a fairly large, thin, frosted glass envelope. Inside the glass is a
gas such as argon and/or nitrogen. At the center of the lamp is a
tungsten filament. Electricity heats this filament up to about 4,500
degrees F (2,500 degrees Celsius). Just like any hot metal, the tungsten
gets "white hot" at that heat and emits a great deal of visible light in a process called incandescence.
A
normal light bulb is not very efficient, and it only lasts about 750 to
1,000 hours in normal use. It's not very efficient because, in the
process of radiating light, it also radiates a huge amount of infrared
heat -- far more heat than light. Since the purpose of a light bulb is
to generate light, the heat is wasted energy. It doesn't last very long
because the tungsten in the filament evaporates and deposits on the
glass. Eventually, a thin spot in the filament causes the filament to
break, and the bulb "burns out."
A halogen lamp also uses a tungsten filament, but it is encased inside a much smaller quartz envelope.
Because the envelope is so close to the filament, it would melt if it
were made from glass. The gas inside the envelope is also different --
it consists of a gas from the halogen group.
These gases have a very interesting property: They combine with
tungsten vapor. If the temperature is high enough, the halogen gas will
combine with tungsten atoms as they evaporate and redeposit them on the filament. This recycling
process lets the filament last a lot longer. In addition, it is now
possible to run the filament hotter, meaning you get more light per unit
of energy. You still get a lot of heat, though; and because the quartz
envelope is so close to the filament, it is extremely hot compared to a normal light bulb.
See How Gas Lanterns Work for more information on incandescence ...
