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10: LED (Light Emitting Diodes)

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    Most forward biased diodes give off heat when electrons "fall" into the lower energy hole of the PN junction as a result of the conservation of energy.  In the case of an LED light is emitted, and this light is of a specific energy (frequency) that is related to the bandgap energy of the PN junction.  So LEDs can be of specific wavelengths


    Single Color LEDs

    Since LEDs are diodes they are polar and must be hooked up correctly.  Figure \(\(PageIndex{1}\) shows a typical LED and you can note that one lead is longer than the other.  The longer lead is the Anode, which you hook to the positive terminal, and the shorter lead is the cathode, which you hook to the negative terminal

    clipboard_ee2a582ea8feff12254ce9817349adb4c.pngFigure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)

    the electronic symbol of an LED is that of a diode with two arrows leaving, to indicate that light is being emitted

    clipboard_e3bb5660a8ad097c8b73087b050c42875.pngFigure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)

    The following shows a Fritzing of a circuit set up on a breadboard for and LED diode.  Note, the long lead is indicated by a bend, so they can line up with the breadboard pin holes. In this circuit it does not matter where the resister is (either before or after the diode).

    clipboard_e014d54f84ebb20b0b85c34adbcfcab47.pngFigure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)









    Red Green and Blue can be combined to form different colors and you should go to this RGB calculator at W3 Schools. to see the different colors that can  be created by mixing various quantities of Red, Green and Blue.  In a RGB LED you have three close LEDS (RG&B) and by varying the amount of current through each you can change the output colore. The following Fritzing has a GRB LED that is set to 1 by default (values vary from 0 to 1), and you can adjust each color by double clicking on it and choosting edit component.  Try changing the green to 0.5 and the blue to 0.2, or make any two of them zero and the third 1.  I coding 8 bits are often used to define the values, and so you can have values from 0 to 255.

    Common Cathode and Andoe RGB LEDs

    An RGB diode has 4 leads, and there are two types. 

    • Common anode you hook the long lead to the hot,
    • Common cathode you hook the long lead to the ground.  
    clipboard_e9db4f3baa632f68da0df75c38832c0ee.pngFigure \(\PageIndex{1}\): Copy and Paste Caption here. (Copyright; author via source)





    This page titled 10: LED (Light Emitting Diodes) is shared under a not declared license and was authored, remixed, and/or curated by Robert Belford.

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