Editing Electric light (section)

=== Carbon arc ===
{{Main|Arc lamp}}
[[File:Xenon short arc 1.jpg|thumb|The 15 kW [[Xenon arc lamp|xenon short-arc lamp]] used in the [[IMAX]] projection system.]]
[[File:Microscope MercuryArcBulb Detail.jpg|thumb|right|A [[mercury (element)|mercury]] arc lamp from a [[fluorescence microscope]].]]
Carbon arc lamps consist of two carbon rod [[electrode]]s in open air, supplied by a current-limiting [[Electrical ballast|ballast]]. The [[electric arc]] is struck by touching the rod tips then separating them. The ensuing arc produces a white-hot [[Plasma (physics)|plasma]] between the rod tips. These lamps have higher efficacy than filament lamps, but the carbon rods are short-lived and require constant adjustment in use, as the intense heat of the arc erodes them.<ref name=edison >{{Cite web|url=http://www.edisontechcenter.org/ArcLamps.html |title=Arc Lamps – How They Work & History |last=Center|first=Edison Tech |website=www.edisontechcenter.org|access-date=2018-01-13|url-status = live|archive-url=https://web.archive.org/web/20170617231552/http://www.edisontechcenter.org/ArcLamps.html |archive-date=2017-06-17}}</ref> The lamps produce significant [[ultraviolet]] output, they require ventilation when used indoors, and due to their intensity they need protection from direct sight.

Invented by [[Humphry Davy]] around 1805, the carbon arc was the first practical electric light.<ref name="Whelan">{{cite web |last=Whelan |first=M. |date=2013 |title=Arc Lamps |url=http://www.edisontechcenter.org/ArcLamps.html |url-status=live |archive-url=https://web.archive.org/web/20141110140158/http://www.edisontechcenter.org/ArcLamps.html |archive-date=November 10, 2014 |access-date=November 22, 2014 |work=Resources |publisher=[[Edison Tech Center]]}}</ref><ref name="Sussman">{{cite book |last1=Sussman |first1=Herbert L. |url=https://books.google.com/books?id=sTbPkEXsA5QC&dq=%22arc+lamp%22&pg=PA124 |title=Victorian Technology: Invention, Innovation, and the Rise of the Machine |date=2009 |publisher=ABC-CLIO |isbn=978-0275991692 |pages=124 |doi= |id=}}</ref> It was used commercially beginning in the 1870s for large building and street lighting until it was superseded in the early 20th century by the incandescent light.<ref name="Whelan" /> Carbon arc lamps operate at high power and produce high intensity white light. They also are a point source of light. They remained in use in limited applications that required these properties, such as [[movie projector]]s, [[stage lighting]], and [[searchlight]]s, until after World War II.<ref name=edison />