A light-emitting diode (LED) is a semiconductor device that creates light using solid-state electronics. A diode is composed of a layer of electron rich material separated by a layer of electron deficient material which forms a junction. Power applied to this junction excites the electrons in the electron rich material leading to photon emission and the creation of light. Depending on the chemical composition of the semiconductor layers, the color of light emission will vary within the electromagnetic spectrum.
The individual diodes are grouped together to form a traffic signal where depending on the individual LED size up to several hundred “lamps” are packaged into an array to form a traffic signal head. Two styles of LED traffic signals known as the diffused and pixilated style are commonly used. In the pixilated style the actual LED array is visible within the traffic signal head while the diffused lens provides a uniform appearance similar to an incandescent signal.
LED’s are much more energy efficient than their incandescent counterparts for several reasons. LED’s produce uniform light dispersion and light output is dispersed evenly over the lens which make them brighter than incandescent lamps. LED’s are very energy efficient producing up to 90 percent light output with very little heat while incandescent bulbs use up to 90 percent of their energy generating heat. Incandescent lamps only produce white light which must be filtered for traffic signal use, and this leads to an additional loss in energy. LEDs, on the other hand, produce colored light that does not need to be filtered out – all of the energy is concentrated around one color band and none is “wasted” on undesired colors.
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