More about Light Emitting Diodes (LEDs)
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Light emitting diodes are small lighting elements used in a wide range of electronic devices, such as digital clocks, audio receivers, VCRs and DVD players. Typically, a light emitting diode is made from an aluminum-gallium-arsenide that is doped with another material to allow for partial conduction of electrons. When an electric current is directed to the diode, it generates light.
The color of the light depends on the makeup of the diode. Aluminum-gallium-arsenide LEDs typically produce a red or infrared light, but other colors are easily generated. For example, blue LEDs can be produced by gallium nitride, silicon carbide substrates and zinc selenide. Green, yellow, orange and even ultraviolet LEDs are also available, and are now manufactured regularly, whereas originally only red and infrared lights were produced.
The main key to understanding how LEDs function is the p-n junction. This is a structure within the diode that allows for the flow of current in a single direction. Simply put, the p-n junction is the location between two sections of the diode, one with extra negatively charged particles (the n-type material) and one with extra holes for these particles (essentially a positively charged side; the p-type material). Electrodes are connected to both ends of the diode; when these electrodes do not induce voltage, the diode acts as an insulator, because particle holes in the p-type material are filled by free electrons. However, when current is introduced to the diode in the right direction, the electrons begin to move across it. This causes the electrons to drop from a higher orbital to a lower one, thereby generating energy, which we perceive as light. Larger shifts create different colors of light.
Although more expensive than most bulbs, LEDs are far more efficient, as they lose little energy as heat. While their cost originally limited them to specific electronic applications, the advances in semiconductors have greatly expanded the possibilities of their use.