Editing Headlamp (section)

=== {{Anchor|High-intensity discharge|HID|Xenon}} High-intensity discharge (HID) ===
{{unreferenced section|date=November 2012}}
[[File:Lincoln xenon headlamp.jpg|thumb|right|HID projector low beam headlamp illuminated on a [[Lincoln MKS]]]]

[[High-intensity discharge lamp]]s (HID) produce light with an [[electric arc]] rather than a glowing filament. The high intensity of the arc comes from metallic salts that are vaporized within the arc chamber. These lamps have a higher efficacy than tungsten lamps. Because of the increased amounts of light available from HID lamps relative to halogen bulbs, HID headlamps producing a given beam pattern can be made smaller than halogen headlamps producing a comparable beam pattern. Alternatively, the larger size can be retained, in which case the HID headlamp can produce a more robust beam pattern.{{original research inline|date=November 2012}}

Automotive HID may be generically called "xenon headlamps", though they are actually [[metal-halide lamp]]s that contain [[xenon]] gas. The xenon gas allows the lamps to produce minimally adequate light immediately upon start, and shortens the run-up time. The usage of [[argon]], as is commonly done in street lights and other stationary metal-halide lamp applications, causes lamps to take several minutes to reach their full output.

The light from HID headlamps can exhibit a distinct bluish tint when compared with tungsten-filament headlamps.

==== Retrofitment ====
When a halogen headlamp is retrofitted with an HID bulb, light distribution and output are altered.<ref name="NHTSAR">{{cite web|url= http://www.nhtsa.gov/cars/rules/rulings/glare.html|title= Glare from Headlamps and other Front Mounted Lamps Federal Motor Vehicle Safety Standard No. 108; Lamps, Reflective Devices, and Associated Equipment|access-date= 4 November 2012|archive-date= 27 September 2011|archive-url= https://web.archive.org/web/20110927155258/http://www.nhtsa.gov/cars/rules/rulings/glare.html|url-status= dead}}</ref> In the United States, vehicle lighting that does not conform to FMVSS 108 is not street legal.<ref name="NHTSAR"/> Glare will be produced and the headlamp's type approval or certification becomes invalid with the altered light distribution, so the headlamp is no longer street-legal in some locales.<ref name="hella">{{cite web |url=http://dsl.torque.net/images/techdocs/Hella_No_Retrofit.jpg |title=Be Careful: Dangerous Products! HID kits and the law |publisher=Hella |access-date=29 May 2014 |url-status=dead |archive-url=https://web.archive.org/web/20110514023838/http://dsl.torque.net/images/techdocs/Hella_No_Retrofit.jpg |archive-date=14 May 2011 }}</ref> In the US, suppliers, importers and vendors that offer non-compliant kits are subject to civil fines. By October 2004, the [[National Highway Traffic Safety Administration|NHTSA]] had investigated 24 suppliers and all resulted in termination of sale or recalls.<ref>{{cite web |url=http://www.nhtsa.gov/About+NHTSA/Press+Releases/2004/ci.NHTSA+Illegal+Lighting+Crackdown+Continues.print |title=Nhtsa Illegal Lighting Crackdown Continues |website=Nhtsa.gov |date=19 October 2004 |access-date=29 May 2014 |archive-date=29 May 2014 |archive-url=https://web.archive.org/web/20140529232440/http://www.nhtsa.gov/About+NHTSA/Press+Releases/2004/ci.NHTSA+Illegal+Lighting+Crackdown+Continues.print |url-status=dead }}</ref>

In Europe and the many non-European countries applying [[United Nations Economic Commission for Europe#Inland Transport Committee|ECE]] Regulations, even HID headlamps designed as such must be equipped with lens cleaning and automatic self-leveling systems, except on motorcycles.<ref name="hella"/> These systems are usually absent on vehicles not originally equipped with HID lamps.

==== History ====
In 1992 the first production low beam HID headlamps were manufactured by [[Hella (company)|Hella]] and [[Robert Bosch GmbH|Bosch]] beginning in 1992 for optional availability on the [[BMW 7 Series (E32)|BMW 7 Series]].<ref name="100Hella">{{cite book |last1=Behrend |first1=Jürgen |title=Hella 1899-1999 |page=97}}</ref><ref name="Litronic">{{cite journal |title=Litronic – New Automotive Headlamp Technology with Gas Discharge lamp |journal=Automotive Design Engineering |year=1993 |last1=Neumann |first1=Rainer |last2=Woerner |first2=B. |pages=152–156}}</ref> This first system uses a built-in, non-replaceable bulb without a UV-blocking glass shield or touch-sensitive electrical safety cutout, designated D1<ref>{{cite report |chapter=Improved Projector Headlamps Using HID (Litronic) and Incandescent Bulbs |publisher=SAE International |year=1994 |last=Neumann |first=Rainer |title=SAE Technical Paper Series |volume=1 |chapter-url=http://papers.sae.org/940636/ |access-date=2014-12-13 |doi=10.4271/940636}}</ref> – a designation that would be recycled years later for a wholly different type of lamp. The AC ballast is about the size of a building brick.
In 1996 the first American-made effort at HID headlamps was on the 1996–98 [[Lincoln Mark VIII]], which uses reflector headlamps with an unmasked, integral-ignitor lamp made by [[Osram Sylvania|Sylvania]] and designated ''Type 9500''. This was the only system to operate on [[Direct current|DC]], since reliability proved inferior to the AC systems.{{citation needed|date=November 2012}} The Type 9500 system was not used on any other models, and was discontinued after [[Osram]]'s takeover of Sylvania in 1997.{{Citation needed|date=April 2012}} All HID headlamps worldwide presently use the standardized AC-operated bulbs and ballasts.
In 1999 the first worldwide HID headlights for both low and high beam were introduced on the [[Mercedes-Benz CL-Class (C215)]].<ref>http://media.daimler.com/dcmedia/0-921-614233-1-820664-1-0-0-0-0-1-11702-854934-0-1-0-0-0-0-0.html {{Webarchive|url=https://archive.today/20141230100212/http://media.daimler.com/dcmedia/0-921-614233-1-820664-1-0-0-0-0-1-11702-854934-0-1-0-0-0-0-0.html |date=30 December 2014 }} The history of the headlamp: From the candle lamp to motorway mode</ref><ref>{{Cite web|url=https://www.carsome.my/news/item/piercing-the-dark-mercedes-benzs-vehicle-lightings-have-come-a-long-way-part-1-of-2|title=Piercing the dark: Mercedes-Benz's vehicle lightings have come a long way – Part 1 of 2|access-date=28 November 2023|website=carsome.my|date=23 January 2020 }}</ref>

==== Operation ====
HID headlamp bulbs do not run on low-voltage DC current, so they require a [[ballast (electrical)|ballast]] with either an internal or external ''ignitor''. The ignitor is integrated into the bulb in D1 and D3 systems, and is either a separate unit or part of the ballast in D2 and D4 systems. The ballast controls the current to the bulb. The ignition and ballast operation proceeds in three stages:
# Ignition: a [[high voltage]] pulse is used to produce an [[electrical arc]] – in a manner similar to a [[spark plug]] – which ionizes the xenon gas, creating a conducting channel between the tungsten electrodes. Electrical resistance is reduced within the channel, and current flows between the electrodes.
# Initial phase: the bulb is driven with controlled overload. Because the arc is operated at high power, the temperature in the capsule rises quickly. The metallic salts vaporize, and the arc is intensified and made [[spectral power distribution|spectrally]] more complete. The resistance between the electrodes also falls; the electronic ballast control gear registers this and automatically switches to continuous operation.
# Continuous operation: all metal salts are in the vapor phase, the arc has attained its stable shape, and the [[luminous efficacy]] has attained its nominal value. The ballast now supplies stable electrical power so the arc will not flicker. Stable operating voltage is 85 [[volt]]s [[alternating current|AC]] in D1 and D2 systems, 42 volts AC in D3 and D4 systems. The frequency of the square-wave alternating current is typically 400 [[hertz]] or higher.
[[File:High Beam Indicator.svg|alt=high beam indicator example|thumb|Headlight indicator example]]
The command is often near the steering wheel and a specific indicator is shown on the dashboard.

==== Bulb types ====
[[File:2014 Toyota Avalon Quadrabeam Headlamp.jpg|thumb|2014 [[Toyota Avalon]] headlamp with "Quadrabeam"-styled HID low beams, halogen high beams, and [[Light-emitting diode|LED]] [[daytime running light]]s that also illuminate at a lower intensity to provide the [[Automotive lighting#Front position lights|front position light]] function]]

HID headlamps produce between 2,800 and 3,500 lumens from between 35 and 38 watts of electrical power, while halogen filament headlamp bulbs produce between 700 and 2,100 lumens from between 40 and 72 watts at 12.8&nbsp;V.<ref name=R37>{{cite web|url= http://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/R037r7e.pdf |title=ECE Regulation 37 for motor vehicle filament bulbs }}&nbsp;{{small|(1.78&nbsp;MB)}}</ref><ref>{{cite web|url= https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/2015/R099r3e.pdf |title=ECE Regulation 99 for motor vehicle HID bulbs }}&nbsp;{{small|(268&nbsp;KB)}}</ref><ref>{{cite web|url=http://fmvss108.tripod.com/light_source_list.htm |title=49CFR564 Replaceable Bulb Headlamp Light Source List |website=Fmvss108.tripod.com |access-date=2010-12-29}}</ref>

Current-production bulb categories are D1S, D1R, D2S, D2R, D3S, D3R, D4S, and D4R. The ''D'' stands for ''discharge'', and the number is the type designator. The final letter describes the outer shield. The arc within an HID headlamp bulb generates considerable short-wave [[ultraviolet]] (UV) light, but none of it escapes the bulb, for a UV-absorbing hard glass shield is incorporated around the bulb's arc tube. This is important to prevent degradation of UV-sensitive components and materials in headlamps, such as [[polycarbonate]] lenses and reflector hardcoats. "S" lamps – D1S, D2S, D3S, and D4S – have a plain glass shield and are primarily used in projector-type optics. "R" lamps – D1R, D2R, D3R, and D4R – are designed for use in reflector-type headlamp optics. They have an opaque mask covering specific portions of the shield, which facilitates the optical creation of the light-dark boundary (cutoff) near the top of a low-beam light distribution. Automotive HID lamps emit considerable near-UV light, despite the shield.

[[File:2014 Toyota Corolla LED Headlight.jpg|thumb|2014 [[Toyota Corolla]] The low beam features LED lighting, halogen high beams, and [[Light-emitting diode|LED]] [[daytime running light]]s that also illuminate at a lower intensity to provide the [[Automotive lighting#Front position lights|front position light]] function]]

==== Color ====
The [[correlated color temperature]] of factory installed automotive HID headlamps is between 4200K while tungsten-halogen lamps are at 3000K to 3550K. The [[spectral density#Applications|spectral power distribution]] (SPD) of an automotive HID headlamp is discontinuous and spikey while the SPD of a filament lamp, like that of the sun, is a continuous curve. Moreover, the [[color rendering index]] (CRI) of tungsten-halogen headlamps (98) is much closer than that of HID headlamps (~75) to standardized sunlight (100). Studies have shown no significant safety effect of this degree of CRI variation in headlighting.<ref>{{cite journal|title=Mercury-free HID headlamps: glare and color rendering|journal=University of Michigan Transportation Research Institute|year=2006 |first1=M. |last1=Sivak |first2=Michael J. |last2=Flannagan |first3=B. |last3=Schoettle |url= http://deepblue.lib.umich.edu/bitstream/2027.42/55201/1/UMTRI-2004-37.pdf|access-date=2009-08-03 }}</ref><ref>{{cite journal |title=Ranges of stop sign chromaticity under tungsten-halogen and high-intensity discharge illumination |journal=University of Michigan Transportation Research Institute |year=1992 |first1=Michael J. |last1=Flannagan |first2=Juha |last2=Luoma |first3=A.W. |last3=Gellatly |first4=M. |last4=Sivak |url=http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005511681&local_base=UMTRI_PUB |access-date=2009-08-03 |archive-date=19 October 2015 |archive-url=https://web.archive.org/web/20151019013407/http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005511681&local_base=UMTRI_PUB |url-status=dead }}</ref><ref>{{cite journal |title=Colors of retroreflective traffic sign materials when illuminated by high-intensity-discharge headlights |journal=University of Michigan Transportation Research Institute |year=1989 |first1=Michael J. |last1=Flannagan |first2=M. |last2=Sivak |url=http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005505889&local_base=UMTRI_PUB |access-date=2009-08-03 |archive-date=19 October 2015 |archive-url=https://web.archive.org/web/20151019013407/http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005505889&local_base=UMTRI_PUB |url-status=dead }}</ref><ref>{{cite journal |title=In-traffic evaluations of high-intensity discharge headlamps: overall performance and color appearance of objects |journal=University of Michigan Transportation Research Institute |year=1993 |first1=M. |last1=Sivak |first2=T. |last2=Sato |first3=D.S. |last3=Battle |first4=E.C. |last4=Traube |first5=Michael J. |last5=Flannagan |url=http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005512803&local_base=UMTRI_PUB |access-date=2009-08-03 |archive-date=19 October 2015 |archive-url=https://web.archive.org/web/20151019013407/http://mirlyn-classic.lib.umich.edu/F/?func=direct&doc_number=005512803&local_base=UMTRI_PUB |url-status=dead }}</ref>

==== Advantages ====

===== Increased safety =====
Automotive HID lamps offer about 3000 [[lumen (unit)|lumen]]s and 90 [[Candela|Mcd]]/m<sup>2</sup> versus 1400 lumens and 30 Mcd/m<sup>2</sup>{{disputed inline|date=November 2012}} offered by halogen lamps. In a headlamp optic designed for use with an HID lamp, it produces more usable light. Studies have demonstrated drivers react faster and more accurately to roadway obstacles with good HID headlamps compared to halogen ones.<ref>{{cite web|url= http://www.lrc.rpi.edu/programs/transportation/pdf/PAL/PAL2001-vanderlofske.pdf |title=Evaluation of High Intensity Discharge Automotive Forward Lighting |access-date=2010-12-29}}</ref> Hence, good HID headlamps contribute to driving safety.<ref>{{cite web|url= http://www.drivingvisionnews.com/index.php?option=com_content&view=article&id=index.php?option=com_content&view=article&id=947 |title=VISION Congress report |website=Drivingvisionnews.com |date=2008-09-02 |access-date=2010-12-29}}</ref> The contrary argument is that glare from HID headlamps can reduce traffic safety by interfering with other drivers' vision.

===== Efficacy and output =====
[[Luminous efficacy]] is the measure of how much light is produced versus how much energy is consumed. HID lamps give higher efficacy than halogen lamps. The highest-intensity halogen lamps, H9 and HIR1, produce 2100 to 2530 lumens from approximately 70 watts at 13.2 volts. A D2S HID bulb produces 3200 lumens from approximately 42 watts during stable operation.<ref name=R37/> The reduced power consumption means less fuel consumption, with resultant less {{CO2}} emission per vehicle fitted with HID lighting (1.3 g/km assuming that 30% of an engine running time is with the lights on).

===== Longevity =====
The average service life of an HID bulb is 2000 hours, compared to between 450 and 1000 hours for a halogen lamp.<ref>{{cite web |url=http://www.friarsmarketing.com/Resources/Lighting%20Programme%20Autom%2367.pdf |title=Osram Automotive Lamps Lighting Programme 2005–06 |website=Friarsmarketing.com |access-date=2010-12-29 |url-status=dead |archive-url= https://web.archive.org/web/20080612073847/http://www.friarsmarketing.com/Resources/Lighting%20Programme%20Autom |archive-date=12 June 2008}}</ref>

==== Disadvantages ====

===== Glare =====
Vehicles equipped with HID headlamps (except motorcycles) are required by [[World Forum for Harmonization of Vehicle Regulations|ECE regulation 48]] also to be equipped with [[headlamp lens cleaning system]]s and automatic beam leveling control. Both of these measures are intended to reduce the tendency for high-output headlamps to cause high levels of [[Glare (vision)|glare]] to other road users. In North America, ECE R48 does not apply and while lens cleaners and beam levelers are permitted, they are not required;<ref>{{cite web |url=http://www.motivemag.com/pub/feature/tech/Motive_Tech_The_Difference_Between_US_and_European_Lights.shtml |title=The Difference Between US and European Lights |website=Motivemag.com |access-date=2010-12-29 |url-status=dead |archive-url=https://web.archive.org/web/20090501102913/http://www.motivemag.com/pub/feature/tech/Motive_Tech_The_Difference_Between_US_and_European_Lights.shtml |archive-date=1 May 2009 }}</ref> HID headlamps are markedly less prevalent in the US, where they have produced significant glare complaints.<ref name="NHTSA_8885"/> Scientific study of headlamp glare has shown that for any given intensity level, the light from HID headlamps is 40% more glaring than the light from tungsten-halogen headlamps.<ref name=Vanderlofske>{{cite web |url=http://www.nhtsa.gov/DOT/NHTSA/NVS/Public%20Meetings/Presentations/2004%20Meetings/VanDerlofske.pdf |title=What Is Glare? p. 24 |website=Webcitation.org |access-date=2012-01-31 |url-status=dead |archive-url= https://web.archive.org/web/20111021132641/http://www.nhtsa.gov/DOT/NHTSA/NVS/Public%20Meetings/Presentations/2004%20Meetings/VanDerlofske.pdf |archive-date=21 October 2011}}</ref>

===== Mercury content =====
HID headlamp bulb types D1R, D1S, D2R, D2S and 9500 contain the toxic [[heavy metals|heavy metal]] [[mercury (element)|mercury]]. The disposal of mercury-containing vehicle parts is increasingly regulated throughout the world, for example under [https://web.archive.org/web/20101229225232/http://www.epa.gov/epawaste/hazard/wastetypes/universal/lamps/index.htm US EPA regulations]. Newer HID bulb designs D3R, D3S, D4R, and D4S which are in production since 2004 contain no mercury,<ref>{{cite web |url=http://www2.prnewswire.com/cgi-bin/stories.pl?ACCT=105&STORY=/www/story/07-27-2004/0002218858 |title=KOITO and DENSO Develop World's First Mercury-Free High-Intensity Discharge Headlamp System |website=Prnewswire.com |access-date=2010-12-29 |url-status=dead |archive-url=https://web.archive.org/web/20210308004434/http://www2.prnewswire.com/cgi-bin/stories.pl?ACCT=105&STORY=%2Fwww%2Fstory%2F07-27-2004%2F0002218858 |archive-date=8 March 2021 }}</ref><ref>{{cite web |url= http://goliath.ecnext.com/coms2/gi_0199-538206/KOITO-and-DENSO-Develop-World.html |title=HID headlamp system has a newly developed mercury-free discharge bulb |website=Goliath.ecnext.com |date=2004-07-27 |access-date=2010-12-29 |url-status=dead |archive-url= https://web.archive.org/web/20090528162933/http://goliath.ecnext.com/coms2/gi_0199-538206/KOITO-and-DENSO-Develop-World.html |archive-date=28 May 2009}}</ref> but are not electrically or physically compatible with headlamps designed for previous bulb types.

===== Cost =====
HID headlamps are significantly more costly to produce, install, purchase, and repair. The extra cost of the HID lights may exceed the fuel cost savings through their reduced power consumption, though some of this cost disadvantage is offset by the longer lifespan of the HID bulb relative to halogen bulbs.