What is an LED?

It's a Light Emitting Diode.

It's more energy efficient than a bulb because it produces less heat than a bulb. I read that some researches had created an LED that was as bright as a bulb. Maybe we'll see them in the shops in a few years time.

LED: Light Emitting Diode. This is a very simple semiconductor device, however, decades of research and developement has improved the LED from a mere novelty to a highly practical device now used in many thousands of applications throughout the world.

Brief history: In the year 1907 the first observations of light coming from a carborundum (SiC) diode was discovered. The light was produced by touching the SiC crystal with electrodes so that a rectifying Schottky contact was formed.

In 1928, Lossev detailed investigations of the luminescence phenomenon observed with SiC metal-semiconductor rectifiers used in radio detection circuits.

Prior to the 1950's, SiC semiconductors had been a well-known material which occurs in nature. The very first LEDs had been made using SiC, however, one publication by Destreiau in 1936 reported LEDs had been made using zincblende (ZnS).

In the early 1960's tremendous growth of the gallium arsenide (GaAs) compound had commenced. Large, single-crystal boules of GaAs were pulled from the melt, then the sliced and polished wafers were used as substrates for the epitaxial growth of P-N junction diode structures. Laser quality light was generated using this method by researchers at RCA, GE, IBM and MIT as early as 1962. However, the diode had to be operated at extremely cold temperatures to keep it from burning out.

The first commercial GaAS (Gallium Arsenide) LED was offered by Texas Instruments Corp. in the early 1960's, it emitted infra-red light around 870 nanometers at a price of $130 each.

The begining of visible light LEDs dates back to the year 1962 when Holonyak and Bevacqua reported on the emission of coherent visible light from a GaAsP (gallium arsenide phophide) junction. This marked the beginning of practical P-N junction LEDs capable of emitting visible light.

The first commercial GaAsP LED was offered by General Electric Corp in the early 1960's. The LED emitted visible red light at room temperature and the cost was $260 each.

Recent advances of the LED have given us new colors (true green, violet, ultra-violet and even "white" (sort of), with amazing brightness that can be clearly seen in direct sunlight and some are used instead of incandescent lamp bulbs in flashlights, automotive signal fixtures, traffic signals, flat panel video displays, etc...

The light output of LEDs does diminish as they are used. It does, however, take a long time for this to happen. Today's new LEDs are fantastic devices, but like everything else in this world, they don't work forever.

Previous answers are correct. LED's are made from a semiconductor in which the current flow raises electrons from the ground state to a higher state; they fall back to the ground state, emitting photons in the process.

Light-Emitting Diode.

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