The Solid-state Lamp, Convenient Uses And Ambitious Plans
A LED (light-emitting diode) converts electrical energy to light by means of a semiconductor, made of a solid material, such as silicon, whose electrical conductivity when hot is as great as that of metals and very low when cold. LEDs were commonly referred to early in their history as solid-state lamps. The light produced by LEDs is known as electroluminescence, distinguishing it from incandescence, which is characteristic of light bulbs.
Semiconductors for LEDs are made from slices of crystal so thin that their lattice, or most basic physical structure, can be easily traversed. This crystal is alloyed with materials of opposing charges, one on each side. The negative side of the semiconductor is electron rich, and the positive side is electron poor. The positive-negative junction formed by the alloyed crystal is known as a depletion layer, which is relatively inactive. The crystal is then subjected to doping, a process of destabilizing
negativity and positivity of the alloys in order to affect their conductivity, so that electrons move in one direction when the semiconductor is held between two electrodes and charged with a current. The electrons shed the energy they pick up from the current in the form of photons, emitting visible light, in order to return to their normal low-energy positions. The color of the emission is determined by its spectral composition. High energy means a short wavelength, which tends toward the blue end of the spectrum. However, while a green diode peaks at green, it can be made to emit an extended range from yellow and orange into red, depending on current flow. It appears red at low current, green at high.