How does a light emitting diode work?

Answer 1

Light Emitting Diodes, commonly called LED's, do dozens of different jobs and are found in all kinds of devices. Among other things, they form the numbers on digital clocks, transmit information from remote controls, light up watches and tell you when your appliances are turned on. Collected together, they can form images on a jumbo TV screen or illuminate a traffic light. :)

Basically, LEDs are just tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescents, they don't have a filament that will burn out, and they don't get especially hot. They are illuminated solely by the movement of electrons in a material, and they last just as long as a standard transistor. Hope this helped.

That talks only about usage, which is all well and good but totally fails to answer the original question of how. Also incandescents operate "solely by the movement of electrons in a material", so that is not really a difference; the difference is in the way those electrons move.

LEDs are ordinary semiconductor diodes, except that they are made of different semiconductors than silicon or germanium. Semiconductors composed of multiple elements that by themselves are not semiconductors (e.g. Aluminum gallium indium phosphide = AlGaInP for red, Indium gallium nitride/Gallium(III) nitride = InGaN/GaN for green, Indium gallium nitride = InGaN for blue). Such semiconductors are different from silicon and germanium in 2 ways:

1. larger bandgap between conduction and valence energy bands
2. transparency to visible light; both silicon and germanium are opaque

The larger bandgap of these semiconductors means that when electrons and holes combine at the junction they release enough energy to produce photons of light, not just phonons which only vibrate the crystal atoms and cause heating as in silicon and germanium with their smaller bandgap. This larger bandgap also means that the forward bias voltage is larger (between ~1V to ~5V depending on material vs. 0.7V for silicon or 0.2V for germanium).

The transparency of these semiconductors allows the photons once generated to escape from the material and be seen, instead of being immediately absorbed as they would in an opaque material and cause heating only.

Going back to the difference in operation between incandescents and LEDs:

• the movement of electrons through the filament of an incandescent light bulb is a phenomenon explained in classical physics, this movement is continuous and causes resistance heating making the filament hot enough to glow
• the movement of electrons (and holes) at the junction in an LED is a phenomenon explained in quantum mechanics, this movement is a sudden jump between energy levels in atoms and directly produces light photons