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How does an LED work

We see LEDs every day. They’re in lotsa stuff. A light-emitting diode (LED) is a semiconductor diode that radiates light (electoluminescence) when current passes through it in the forward direction. Electrons move though semiconductor medium and “fall into” other energy levels during their transit of the p-n junction. When these electrons make a transition to a lower energy level, they give off a photon of light. This photon may be in the infrared region, or just about anywhere across the visible spectrum up to and into ultraviolet – but we have to pick a color when we make them. That means we can get an infrared LED to work in our remote controls, and get other ones of different colors to make indicators or, in large arrays, displays – even color ones.

LEDs uaually are made to emit one color of light, though bicolor ones and more can be fabricated. Intensity is being improved as well. That broadens the applications considerably (think vehicular tail lights). The device has a pair of leads, and a (usually) plastic body moulded around the leads and the semiconductor crystal itself. That way the light can get out through the plastic. There is frequently a “round dome” at the top of the LED which serves to focus the light headed out through it. Remember that it is the material of the semiconductor crystal that determines the light given off by the device. A normal LED isn’t really voltage dependent. When obtaining the LEDs, a manufacturer or hobbiest specifies the color. Red, green and blue are most popular, and, though there are other colors, it might be tough(er) to find them. Note that the big LED color displays use a three-LED pixel, and by driving it (the 3-LED assembly) appropriately, a wide range of colors can be obtained.

This in an introduction to the LED. An electronics student will review semiconductor fundamentals and then more closely examine the chemisty and physics of the particular p-n junction that is fabricated to exhibit electroluminesce. A link is provided to the Wikipedia article on the light-emitting diode.

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