Light emitting diode
A Light emitting diode (LED) is a type of semiconductor (a diode) that emits light when an electric current is passed through it. It is made with many different specialized semiconductor materials so it can give off light when current flows forward through it. Depending on the different types of chemical elements used in making the diode, different colors of light can be produced. Unlike simple semiconductors which usually contain silicon and germanium, the complex semiconductors required to generate light contain more unusual compounds. Although composition varies, gallium arsenide, gallium phosphide and indium phosphide are commonly used in LEDs.
Light emitting diodes at the basic level create only a single color of light. Thus, to create a "white LED" it actually takes more complicated construction. The two ways to create a white LED are to build an LED module that actually has 3 primary color LED chips inside it (red, green, and blue.) This kind of LED can produce many colors by mixing various quantities of each of the 3 primary colors. The most common kind of white LED is that which is used in LED flashlights: It is actually an ultraviolet LED chip covered with phosphor - just like the inside of a fluorescent tube light: The UV light hits the phosphor which in turn gives off yellow-white light which mixes with the blue tint of the UV led to produce a nearly white color.