LEDs are Semiconductor (solid-state) Devices. Like Transistors, and other Diodes, LEDs are made out of Silicon. An LED emits Light, because there are the SMALL amounts of Chemical Impurities, that are added to the Silicon, such as Gallium, Arsenide, Indium, and Nitride. When Current passes through the LED, it emits Photons as a Byproduct. NORMAL Light Bulbs produce Light by heating a Metal Filament, until it's White HOT. Because LEDs produce Photons directly and NOT via Heat, they are FAR MORE EFFICIENT than Incandescant Bulbs.