A light emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly
used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness.
The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with 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 gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output.
They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology.
Practical use Red, yellow and green (unlit) LEDs used in a traffic signal.
The first commercial LEDs were commonly used as replacements for incandescent indicators, and in seven segment displays,first in expensive equipment such as laboratory and electronics test equipment, then later in such appliances as TVs, radios, telephones, calculators, and even watches (see list of signal applications). These red LEDs were bright enough only for use as indicators, as the light output was not enough to illuminate an area. Later, other colors became widely available and also appeared in appliances and equipment. As the LED materials technology became more advanced, the light output was increased, while maintaining the efficiency and the reliability to an acceptable level. The invention and development of the high power white light LED led to use for illumination(see list of illumination applications). Most LEDs were made in the very common 5 mm T1¾ and 3 mm T1 packages, but with increasing power output, it has become increasingly necessary to shed excess heat in order to maintain reliability[20], so more complex packages have been adapted for efficient heat dissipation. Packages for state of the art high power LEDs bear little resemblance to early LEDs.
Analysts say that after 2010, LED lighting will gain a larger market share in the interior lighting market and its broad prospects are not in doubt.
LEDs brightness and adjustable VIS colours help interior lighting meet the requirements of any desired atmosphere or colour. In the developing designer lighting market, traditional light sources can not match LEDs advantages.
Dynamic control of LEDs is easy; they can be designed according to the specific needs of users, and in some occasions can accommodate programmability demands. LED products can provide a range of intelligent solutions, providing convenient, intelligent management interior lighting.
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