The material is called a semiconductor because it is a poor conductor of electricity in its pure form. To make it a better conductor, impurities are added to create “holes” through which the electricity can flow. This process is called doping. When electricity then flows through the material, light is given off. The device is called a diode because it made of two layers of material that force the electricity to flow in one direction from one layer to the other.
LEDs at first could produce only very low levels of light, which meant they could be used only for things like indicator lamps in laboratory and electronic test equipment. Later they were used in TVs, radios, telephones, and calculators. As development continued, the LEDs became bright enough to be used in relatively low-level illumination devices like traffic signals, exit signs, and other specialty purposes. LED lights bulb are now finding applications in automobiles for taillights and in airplanes for interior lighting. Since LED light bulbs are small, to make a larger light source, it is necessary to assemble a number of LEDs into an array.
LED light bulbs are not yet broadly used for general lighting purposes because they generally cannot compete with more traditional light sources like incandescent or fluorescent bulbs on the basis of either performance or cost. The Department of Energy says that while recent research has increased the output of LEDs to produce as much light as 50 to 150 watt incandescent bulbs, the cost of the LED light itself is much higher. For comparison, the cost of an LED light itself is much higher. For comparison, the cost of an LED light in 2006 was about $50 for a 1,000 lumen bulb (about the illumination of an incandescent 75 watt bulb), while the cost of an incandescent bulb of the same illumination was about $1.
