A light-emitting diode (LED) is a two-lead semiconductor light source. It is a pn junction diode, which emits light when activated.[4]hen a suita!le voltage is applied to the leads, electrons are a!le to recom!ine with electron holes within the device, releasing energ" in the #orm o# photons. $his e##ect is called electroluminescence, and the color o# the light (corresponding to the energ" o# the photon) is determined !" the energ" !and gap o# the semiconductor.An %&' is o#ten small in area (less than ( mm)) and integrated optical components ma" !e used to shape its radiation pattern.[*]Appearing as practical electronic components in (+,),[,] the earliest %&'s emitted low-intensit" in#rared light. In#rared %&'s are still #re-uentl" used as transmitting elements in remote-control circuits, such as those in remote controls #or a wide variet" o# consumer electronics. $he #irst visi!le-light %&'s were also o# low intensit", and limited to red. .odern %&'s are availa!le across the visi!le,ultraviolet, and in#rared wavelengths, with ver" high !rightness.&arl" %&'s were o#ten used as indicator lamps #or electronic devices, replacing small incandescent !ul!s. $he" were soon pac/aged into numeric readouts in the #orm o# seven-segment displa"s, and were commonl" seen in digital cloc/s.0ecent developments in %&'s permit them to !e used in environmental and tas/ lighting. %&'s haveman" advantages over incandescent light sources including lower energ" consumption, longer li#etime, improved ph"sical ro!ustness, smaller si1e, and #aster switching. %ight-emitting diodes are now used in applications as diverse as aviation lighting, automotive headlamps, advertising,general lighting, tra##ic signals, camera #lashes and even %&' wallpaper. 2owever, %&'s power#ul enough #or room lighting are still relativel" e3pensive, and re-uire more precise current and heat management than compact #luorescent lamp sources o# compara!le output.Discoveries and early devices[edit]4reen electroluminescence #rom a point contact on a cr"stal o# 5i6recreates 2. 7. 0ound8s original e3periment #rom (+9:.&lectroluminescence as a phenomenon was discovered in (+9: !" the ;ritish e3perimenter 2. 7. 0ound o# .arconi %a!s, using a cr"stal o#silicon car!ide and a cat8s-whis/er detector.[:][