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. There are two ways to create a white LED. The first is 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 second and most common kind of white LED is that which is typically used in LED flashlights and other cheap enectronics: 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.
LEDs offer several advantages over their rivals. Fundamentally, they provide a more efficient conversion of electricity (electrons) into light (photons) than their current competitors. Incandescent lights must consume energy heating the filament to the point that it will glow white-hot. This heat is typically wasted, since only the light is needed from this fixture. Fluorescent lights offer a more efficient conversion, but come with their problems as well. In ideal situations, they are able to last longer and produce less wasted heat. However, they have several functional issues such as poor operation at low temperatures. Compact Fluorescent Lights (CFLs) come with even more issues, since they must have a base which generates the electrical pulses which flash through the tube and produce light. The base tends to overheat itself, especially when it is mounted upside-down or in an enclosure. They also take time to warm up if they are used in cold environments. Another concern with these lights is that they contain mercury gas, which is believed to be toxic and must be disposed of carefully.
LEDs, however, are not significantly sensitive to low temperatures. They produce more light with less electricity, and if designed properly, will outlast incandescent bulbs significantly. However, LEDs do still suffer from heat sensitivity, and will burn out if they are operated at high temperatures. This is known as LED meltdown. They also do not offer true white light by themselves. As described above, they must either be made in groups of three to produce a simulated full-spectrum of color, or be made to produce blue or yellow tinted light. Lastly, LED chips themselves are relatively inexpensive, but consumer bulbs can be fairly expensive.
Incandescent: A 60-watt incandescent light bulb draws over $300 worth of electricity per year and provides about 800 lumens.
Fluorescent: An equivalent compact fluorescent uses less than 15 watts and costs only about $75 of electricity per year.
LED: Offering an equivalent output, LED bulbs draw less than 8 watts of power, costing about $30 per year, and lasting about 50,000 hours