Today's featured picture

Light-emitting diode

A light-emitting diode (LED) is a semiconductor light source that emits light when an electric current flows through it. When a current passes through the diode, which is formed of two different semiconductor materials, electrons are able to recombine with electron holes, releasing energy in the form of photons. This effect is called electroluminescence. The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device. The earliest practical LEDs, which appeared in 1962, emitted low-intensity infrared and red light. Modern LEDs are available with high output in a range of visible, ultraviolet, and infrared wavelengths.

This picture shows three different views of an 11×44 LED matrix lapel name tag display. The top image is of a little over half of the display, the center image is a close-up of the LEDs in ambient light, and the bottom image is the LEDs in their own red light.

Photograph: Janke

Other areas of Wikipedia

  • Community portal – Bulletin board, projects, resources and activities covering a wide range of Wikipedia areas.
  • Help desk – Ask questions about using Wikipedia.
  • Local embassy – For Wikipedia-related communication in languages other than English.
  • Reference desk – Serving as virtual librarians, Wikipedia volunteers tackle your questions on a wide range of subjects.
  • Site news – Announcements, updates, articles and press releases on Wikipedia and the Wikimedia Foundation.
  • Village pump – For discussions about Wikipedia itself, including areas for technical issues and policies.

Wikipedia's sister projects

Wikipedia is hosted by the Wikimedia Foundation, a non-profit organization that also hosts a range of other projects:

Wikipedia languages

Other Languages
bosanski:
català: Portada
čeština: Hlavní_strana
dansk: Forside
eesti: Esileht
Ελληνικά: Πύλη:Κύρια
euskara: Azala
galego: Portada
hrvatski: Glavna_stranica
Bahasa Indonesia: Halaman_Utama
עברית: עמוד_ראשי
latviešu:
magyar: Kezdőlap
Bahasa Melayu: Laman_Utama
Nederlands: Hoofdpagina
norsk nynorsk: Hovudside
Simple English: Main_Page
slovenčina: Hlavná_stránka
slovenščina: Glavna_stran
српски / srpski: Главна_страна
srpskohrvatski / српскохрватски: Glavna_stranica
Türkçe: Ana_Sayfa
українська: Головна_сторінка
Tiếng Việt: Trang_Chính