One of the more revolutionary innovations in lighting is the Light Emitting Diode, or LED. This cutting edge technology was first discovered 103 years ago! However, only comparatively recently have LEDs been either efficient or cheap enough for wide use.
LEDs operate just like any other diode, allowing an electric current to pass, for the most part, in only one direction. They are built by placing into contact a P-type (positive) and an N-type (negative) semiconductor and passing a current from the N to the P materials. In the case of LEDs, when the electrons and holes recombine, light is emitted. In most diodes, heat is emitted. Actually, LEDs do produce some heat as well and this becomes important for reasons to be discussed later.