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 or emits light. In a fluorescent lamp, an electric arc excites mercury atoms, which emit ultraviolet (UV) radiation. After striking the phosphor coating on the inside of glass tubes, the UV radiation is converted and emitted as visible light.

An LED, in contrast, is a semiconductor diode. It consists of a chip of semiconducting material treated to create a structure called a p-n (positive-negative) junction. When connected to a power source, current flows from the p-side or anode to the n-side, or cathode, but not in the reverse direction. Charge-carriers (electrons and electron holes) flow into the junction from electrodes. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon (light).

Color Quality

Color quality has been one of the key challenges facing white light-emitting diodes (LEDs) as a general light source. This section reviews the basics regarding light and color and summarizes the most important color issues related to white light LEDs, including recent advances. Click on the links below for more information.

• Light and Color Basics
• Correlated Color Temperature - CCT
• Color Rendering Index - CRI
• Making White Light with LED
• Luminous Efficacy and Color Characteristics
  

Lifetime of White LEDs

One of the main "selling points" of LEDs is their potentially very long life. Do they really last 50,000 hours or even 100,000 hours? It depends on LED quality, system design, operating environment, and other factors. This section provides information on lumen depreciation and life measurement for LEDs compared to other light sources.

• Lumen Depreciation
• Defining LED Useful Life
• Measuring Light Source Life

Termal Management of White Light LEDs

LEDs won’t burn your hand like some light sources, but they do produce heat. In fact, thermal management is arguably the most important aspect of successful LED system design. This section reviews the role of heat in LED performance and methods for managing it.

• Comparison of Power Conversion of White Light Sources
• Why Does Thermal Management Matter?
• What Determines Junction Temperature?

For more information, please click on the 'Reference' tab above.