Captain Henry Joseph Round was an English engineer and one of the early pioneers of radio. He was the first to report the observation of electroluminescence from a solid state diode, leading to the discovery of the light-emitting diode. He was a personal assistant to Guglielmo Marconi.
Henry Joseph Round
Recreation of the 1907 experiment by H. J. Round on the observation of electroluminescence from a point contact with a carborundum (silicon carbide) crystal
A light-emitting diode (LED) is a semiconductor device that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.
LED in white. The LEDs in this picture are housed in "regular" cases, but there are many variants of LEDs.
A bulb-shaped modern retrofit LED lamp with aluminum heat sink, a light diffusing dome and E27 screw base, using a built-in power supply working on mains voltage
Green electroluminescence from a point contact on a crystal of SiC recreates Round's original experiment from 1907.
Close-up of a 1 watt red power led
