LED Lighting is based on Light Emitting Diode (LED) technology, which results in lamps with significantly reduced energy consumption, but with lifespan and luminous efficacy several times better than that of both incandescent and CFL lamp types.
The Basics
LEDs use what is known as a semiconductor to produce light when an electric current is applied to it. It produces light because the electric current causes electrons within the semiconductor to move around, which releases energy in the form of photons (light). The colour of the light released is dependent on the material used as the semiconductor.
Because most semicondutors produce coloured light, to produce 'white' light that we can use for domestic lighting, a mixture of colours or a phosphor coating (similar to CFLs) is used to create light that appears white.
The Science
The main component of an LED is a 'chip' of semiconducting material, a semiconductor has the electrical conductivity between that of a conductor (e.g. copper wiring) and that of an insulator (e.g. rubber). This semiconductor is doped (intentionally introduced) with impurities, which modify the electrical properties of the semiconductor, in this case creating what is knows as a p-n junction. This p-n junction consists of a p-type (positively charged) side, and an n-type (negatively charged) side, with the negative side having a high concentration of free electrons, and the positive side having a high concentration of electron holes (the conceptual opposite to an electron, or the lack of an electron where one could exist).
When an electronic current is introduced, electrons and holes flow into the junction, and when an electron meets a hole it releases energy in the form of a photon. The wavelength of the light emitted is reliant on the band gap of the semiconductor used. The band gap is equivalent to the energy required to free an outer shell electron from its orbit about its current atom nucleus, to become a mobile charge carrier, and hence join with an electron hole.