We have known for a hundred years how to get certain inorganic materials to emit light when a current is passed through them, and LEDs themselves have existed for some fifty years. These colorful indicator lamps that have no filament or gas filling have been gradually refined and have become available in more varied and vivid colors. In recent years their efficiency has improved to the point that LED technology is replacing even fluorescent lighting. The most recent developments include LEDs that can replace LCDs.