Wikipedia has a very good introduction to LEDs.
What is an LED?
A very basic introduction to how a light-emitting diode works.
Benefits and drawbacks of LEDs
LEDs offer a huge variety of benefits but at the same time they cannot be viewed as the optimum solution for every lighting-related application. Here, in no particular order, we list some of the main advantages of LEDs, together with some of the challenges faced by these devices.
Terminology: LED efficiency
Explaining terms such as external quantum efficiency, extraction efficiency and wall-plug efficiency.
Radiometric and Photometric terms
Explaining terms and units such as radiant flux, luminous efficacy, lumens and candelas.
APPLICATIONS & MARKETS
Please contact the editor, Tim Whitaker, to suggest suitable subject areas for inclusion.