Stands for Light Emitting Diode. L.E.D.s are tiny light bulbs that fit easily into an electrical circuit. But unlike ordinary incandescent bulbs, 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 semiconductor material, and they last just as long as a standard transistor. L.E.D. lights don't force your eyes to re-adjust every time you use them. That makes getting around in the dark much easier.