Editing Metal-halide lamp (section)

{{Short description|Type of lamp}}
{{More citations needed|date=September 2018}}
{{Distinguish|Halogen lamp}}
[[File:Metaalhalidelamp.JPG|thumb|Metal halide lamp bulb (type /O with arc tube shield)]]
[[File:Metal Halide Rainbow.png|thumb|A common [[spectrum]] of metal halide lamps in North America]]
[[File:Mhlightsbaseball.JPG|thumb|Metal halide floodlights at a baseball field]]
[[File:Picture of Charles Proteus Steinmetz.jpg|thumb|Metal halide lamps were invented by [[Charles Proteus Steinmetz]] in 1912 and are now used in almost every city in the world.]]
A '''metal-halide lamp''' is an electrical lamp that produces light by an [[electric arc]] through a gaseous mixture of vaporized [[mercury (element)|mercury]] and [[metal halides]]<ref name="Hordeski">{{cite book|last = Hordeski| first = Michael F.| title = Dictionary of energy efficiency technologies| publisher = [[CRC Press]]| year = 2005| location = USA| pages = 175–176|isbn = 978-0-8247-4810-4}}</ref><ref name="Grondzik">{{cite book|last=Grondzik| first = Walter T.|author2=Alison G. Kwok |author3=Benjamin Stein |author4=John S. Reynolds
|title = Mechanical and Electrical Equipment for Buildings, 11th Ed.| publisher=[[John Wiley & Sons]]|year=2009| location = USA| pages = 555–556|url=https://books.google.com/books?id=EL4nt2VFTZIC&q=%22metal+halide+lamp%22&pg=PA555|isbn = 978-0-470-57778-3}}</ref> (compounds of metals with [[bromine]] or [[iodine]]). It is a type of [[high-intensity discharge]] (HID) [[gas discharge lamp]].<ref name="Hordeski" /> Developed in the 1960s, they are similar to [[mercury vapor lamp]]s,<ref name="Hordeski" /> but contain additional metal halide compounds in the [[quartz]] arc tube, which improve the efficiency and [[color rendering index|color rendition]] of the light.
The most common metal halide compound used is [[sodium iodide]]. Once the arc tube reaches its running temperature, the sodium dissociates from the iodine, adding orange and reds to the lamp's spectrum from the sodium D line as the metal ionizes.
As a result, metal-halide lamps have high [[luminous efficacy]] of around 75–100 lumens per watt,<ref name="Grondzik" /> which is about twice that of mercury vapor lights and 3 to 5 times that of [[incandescent light]]s<ref name="Hordeski" /> and produce an intense white light.  Lamp life is 6,000 to 15,000 hours.<ref name="Grondzik" /><ref name="TERI">{{cite book   
  | title = Light Right: A practising engineer's manual on energy-efficient lighting
  | publisher = TERI Press
  | year = 2004
  | pages = 19–20
  | url = https://books.google.com/books?id=ZoLC0vgtewwC&q=%22metal+halide+lamp%22+gas+discharge+mercury&pg=PA19
  | isbn = 978-81-7993-044-1}}</ref>  As one of the most efficient sources of high [[Color rendering index|CRI]] white light, metal halides {{As of|2005|alt=as of 2005}} were the fastest growing segment of the lighting industry.<ref name="Hordeski" />  They are used for wide area overhead lighting<ref name="Grondzik" /> of commercial, industrial, and public places, such as parking lots, sports arenas, factories, and retail stores,<ref name="Hordeski" /> as well as residential [[security lighting]], [[automotive headlamp]]s (Often [[Generic trademark|generically]] known as "[[Xenon HID headlamp|xenon headlights]]") and indoor cannabis grow operations.

The lamps consist of a small [[fused quartz]] or [[ceramic]] [[arc tube]] which contains the gases and the arc, enclosed inside a larger glass bulb (Or quartz bulb with a coating to filter out the [[ultraviolet light]] produced in the case of compact lamps).<ref name="Hordeski" /><ref name="TERI" /> They operate at a pressure between 4 and 20 atmospheres, and require special fixtures to operate safely, as well as an electrical [[ballast (electrical)|ballast]]. Metal atoms produce most of the light output.<ref name="Hordeski" /> They require a warm-up period of several minutes to reach full light output.<ref name="Grondzik" />