LEDs differ from traditional light sources in the way they produce light. In an incandescent lamp, a tungsten filament is heated by electric current until it glows, emitting light. In a fluorescent lamp, an electric current causes the gas inside the tube to emit ultraviolet (UV) radiation, which strikes the phosphor coating on the inside of the glass, causing it to emit visible light.

An LED, on the other hand, is a semiconductor diode, a device that allows current to flow in only one direction. It's made of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. The positive side contains excess positive charge ("holes," indicating the absence of electrons) while the negative side contains excess negative charge (electrons).

When current is applied, the negatively-charged electrons move toward the positive side, and the positively-charged “holes” move toward the negative side. At the junction, the electrons and holes combine. As this occurs, energy is released in the form of light that is emitted by the LED.

Depending on the alloy used to make the semiconductor, the light emitted by the LED can range through the colors of the rainbow: red, orange, yellow, green, and blue. "White" light is created by combining the light from red, green, and blue (RGB) LEDs, or by coating a blue LED with yellow phosphor.

Source: UF/IFAS Energy Efficient Homes: Introduction to LED Lighting, Barbara Haldeman, Wendell A. Porter, Kathleen C. Ruppert, 2008.

Additional Resources

UF IFAS Energy Efficient Homes: Introduction to LED Lighting - http://edis.ifas.ufl.edu/FY1049

Using LEDs for General Illumination http://www1.eere.energy.gov/buildings/ssl/using_leds.html

Solid State Lighting Luminaires http://www.energystar.gov/index.cfm?c=new_specs.ssl_luminaires

LEDs http://www.lrc.rpi.edu/researchAreas/leds.asp

LED Lighting http://www.toolbase.org/Building-Systems/Electrical-Electronics/white-LED-lighting

Introduction to LED Lighting - http://lightingdesignlab.com/articles/LED_fund/intro_ledfund.htm