LED light-emitting diode In electronics terms, a diode is a semiconductor device through which current can go in only one direction. As a side effect, light-emitting diodes produce either visible or infrared light. LEDs require very little power and are often used as indicator lights, including (most likely) the drive access lights on your computer. LEDs are also found in some "laser-quality" printers. See also: diode, laser printer, semiconductor