Light Emitting Diode
Light Emitting Diodes (LEDs) are semiconductor light sources. They operate on the principle of electroluminescence in which a material emits light in response to the passage of electric current or applied electric fields. The light emitted can be of various colors depending upon the bandgap in the semiconducting material used to create the diode. This operating principle is different than thermoluminescence where a material emits light due to its elevated temperatures. This small LED was removed from a USB Memory Stick. At the top of the LED is one of the two electrical connections, the other attaches to the bottom of the device and is hidden from view. Compare this to the filament of an incandescent light bulb.