Editing Headlamp (section)

=== Construction, performance, and aim ===
There are two different beam pattern and headlamp construction standards in use in the world: The [[World Forum for Harmonization of Vehicle Regulations|ECE]] standard, which is allowed or required in virtually all industrialized countries except the United States, and the [[Society of Automotive Engineers|SAE]] [[Federal Motor Vehicle Safety Standard 108|standard]] that is mandatory only in the US. Japan formerly had bespoke lighting regulations similar to the US standards, but for the left side of the road. However, Japan now adheres to the ECE standard. The differences between the SAE and ECE headlamp standards are primarily in the amount of glare permitted toward other drivers on low beam (SAE permits much more glare), the minimum amount of light required to be thrown straight down the road (SAE requires more), and the specific locations within the beam at which minimum and maximum light levels are specified.

ECE low beams are characterized by a distinct horizontal "cutoff" line at the top of the beam. Below the line is bright, and above is dark. On the side of the beam facing away from oncoming traffic (right in right-traffic countries, left in left-traffic countries), this cutoff sweeps or steps upward to direct light to road signs and pedestrians. SAE low beams may or may not have a cutoff, and if a cutoff is present, it may be of two different general types: ''VOL'', which is conceptually similar to the ECE beam in that the cutoff is located at the top of the left side of the beam and aimed slightly below horizontal, or ''VOR'', which has the cutoff at the top of the right side of the beam and aimed at the horizon.<ref name="WDTGCF">{{cite web |url= http://dmses.dot.gov/docimages/pdf82/176157_web.pdf |title= "Where Does The Glare Come From?" (NHTSA glare response + white paper on headlamp performance, glare, and regulation) |url-status= dead |archive-url= https://web.archive.org/web/20030803104147/http://dmses.dot.gov/docimages/pdf82/176157_web.pdf |archive-date= 3 August 2003}}&nbsp;{{small|(463&nbsp;KB)}}</ref>

Proponents of each headlamp system decry the other as inadequate and unsafe: US proponents of the SAE system claim that the ECE low beam cutoff gives short seeing distances and inadequate illumination for overhead road signs, while international proponents of the ECE system claim that the SAE system produces too much glare.<ref>{{cite web |last=Grueninger |first=Wes |title=Prometheus, Bound: The Difference Between American and European Car Lighting |website=MotiveMag.com |date=5 March 2008 |url= http://www.motivemag.com/pub/feature/tech/Motive_Tech_The_Difference_Between_US_and_European_Lights.shtml |access-date=29 May 2014 |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> Comparative studies have repeatedly shown that there is little or no overall safety advantage to either SAE or ECE beams; the two systems' acceptance and rejection by various countries is based primarily on which system is already in use.<ref name="WDTGCF"/><ref name="Dayton">{{Cite web|url=https://www.regulations.gov/document/NHTSA-2001-8885-1508|title=Regulations.gov|website=www.regulations.gov}}</ref>

In North America, the design, performance, and installation of all [[Automotive lighting|motor vehicle lighting]] devices are regulated by [[Federal Motor Vehicle Safety Standard 108|Federal and Canada Motor Vehicle Safety Standard 108]], which incorporates [[Society of Automotive Engineers|SAE]] technical standards. Elsewhere in the world, ECE [[World Forum for Harmonization of Vehicle Regulations|internationalized regulations]] are in force either by reference or by incorporation in individual countries' vehicular codes.

US laws required [[sealed beam]] headlamps on all vehicles between 1940 and 1983, and other countries such as Japan, United Kingdom, and Australia also made extensive use of sealed beams.{{when|date=January 2014}} In most other countries, and in the US since 1984, replaceable-bulb headlamps predominate.

Headlamps must be kept in proper aim.<ref>{{cite web|url=http://www.searchautoparts.com/aftermarket-business/newsmaker/international-newsmaker-q-daniel-stern |first=James E. |last=Guyette |title=International Newsmaker Q&A: Daniel Stern |website=Searchautoparts.com |date=19 October 2012 |access-date=29 May 2014}}</ref> Regulations for aim vary from country to country and from beam specification to beam specification. In the US, SAE standard headlamps are aimed without regard to headlamp mounting height. This gives vehicles with high-mounted headlamps a seeing distance advantage, at the cost of increased glare to drivers in lower vehicles. By contrast, ECE headlamp aim angle is linked to headlamp mounting height, to give all vehicles roughly equal seeing distance and all drivers roughly equal glare.<ref name="aim">{{cite web|url= http://www.danielsternlighting.com/tech/aim/aim.html |title=Headlamp aiming specifications & procedures |website=Danielsternlighting.com |date=October 2012 |access-date=29 May 2014}}</ref>

==== Light colour ====
=====White=====
Headlamps are generally required to produce white light, according to both ECE and SAE standards. ECE Regulation 48 currently requires new vehicles to be equipped with headlamps emitting white light.<ref name="R48"/> Different headlamp technologies produce different characteristic types of white light; the white specification is quite large and permits a wide range of apparent colour from warm white (with a brown-orange-amber-yellow cast) to cold white (with a blue-violet cast).

===== Selective yellow =====
[[File:Kerkrade 2CV Front.jpg|thumb|upright|1957 [[Citroën 2CV]] with [[selective yellow]] headlamps and auxiliary lamp]]Previous ECE regulations also permitted [[selective yellow]] light. A research experiment done in the UK in 1968 using tungsten (non-halogen) lamps found that visual acuity is about 3% better with selective yellow headlamps than with white ones of equal intensity.<ref name=LR156>{{cite report |last1=Christie |first1=A.W. |last2=Ashwood |first2=J.E. |last3=Symons |first3=R.D.H. |year=1968 |title=Visual Acuity in Yellow Headlights |publisher=UK Ministry of Transport Road Research Laboratory |id=LR 156 |url=https://trl.co.uk/sites/default/files/LR156.pdf |archive-url=https://web.archive.org/web/20180729230449/https://trl.co.uk/sites/default/files/LR156.pdf |archive-date=2018-07-29 |access-date=29 July 2018}}</ref> Research done in the Netherlands in 1976 concluded that yellow and white headlamps are equivalent as regards traffic safety, though yellow light causes less discomfort glare than white light.<ref name=SWOV1976>{{cite report |year=1976 |title=White or Yellow Light for Vehicle Head-Lamps? |publisher=SWOV Institute for Road Safety Research |id=1976-2E |url=https://www.swov.nl/publicatie/white-or-yellow-light-vehicle-head-lamps |access-date=29 July 2018}}</ref> Researchers note that tungsten filament lamps emit only a small amount of the blue light blocked by a selective-yellow filter,<ref name=LR156/> so such filtration makes only a small difference in the characteristics of the light output,<ref name=Snow>{{cite journal|title=Driving in Snow: Effect of Headlamp Color at Mesopic and Photopic Light Levels|journal=SAE Technical Paper Series|year=2001|first1=John|last1=Bullough |first2=Mark S. |last2=Rea |volume=1 |doi=10.4271/2001-01-0320 |url= http://www.lightingresearch.org/programs/transportation/pdf/SAE/2001-01-0320.pdf|archive-url= https://web.archive.org/web/20060223111121/http://www.lightingresearch.org/programs/transportation/pdf/SAE/2001-01-0320.pdf|url-status=dead|archive-date=2006-02-23|access-date=2010-01-27}}</ref> and suggest that headlamps using newer kinds of sources such as metal halide (HID) bulbs may, through filtration, give off less visually distracting light while still having greater light output than halogen ones.<ref name=Snow/>

Selective yellow headlamps are no longer common, but are permitted in various countries throughout Europe{{vague|date=November 2014}} as well as in non-European locales such as South Korea, Japan<ref>[http://retail.ihs.com/abstracts/jsa/jis-d-5500.jsp Japanese Industrial Standard JIS D-5500] {{webarchive|url=https://web.archive.org/web/20070815142229/http://retail.ihs.com/abstracts/jsa/jis-d-5500.jsp |date=15 August 2007 }} ''Automobile Parts--Lighting and Light Signaling Devices'' p. 5, sec. 4.4.2, table #4</ref> and New Zealand.<ref>{{cite web|url=http://landtransport.govt.nz/certifiers/virm-in-service/general-v3.pdf |title=New Zealand Vehicle Inspection Requirement Manual p. 4.1.2 |website=Landtransport.govt.nz |access-date=2012-01-31}}</ref> In [[Iceland]], yellow headlamps are allowed<ref>[http://ww2.us.is/sw_documents/421 Icelandic Transport Authority US.321 Information on permitted headlight equipment on vehicles in Iceland.(46 KB)] {{webarchive|url=https://web.archive.org/web/20131203001807/http://ww2.us.is/sw_documents/421 |date=3 December 2013 }}''Information on allowed headlight equipment.'' Umferðastofa Íslands {{cite web |url=http://ww2.us.is/ |title=Umferðarstofa |access-date=2013-11-25 |url-status=dead |archive-url=https://web.archive.org/web/20131122103926/http://ww2.us.is/ |archive-date=22 November 2013}} Retrieved 2013-11-25.</ref> and the vehicle regulations in [[Monaco]] still officially require selective yellow light from all vehicles' low beam<ref>{{Cite web|url=http://www.legimonaco.mc/305/legismclois.nsf/Code/8F0D3ABE9EA3E9C6C125773F002D89D7!OpenDocument|title=LégiMonaco - Code De La Route - Article 76|date=3 March 2016|archive-url=https://web.archive.org/web/20160303220436/http://www.legimonaco.mc/305/legismclois.nsf/Code/8F0D3ABE9EA3E9C6C125773F002D89D7!OpenDocument |archive-date=3 March 2016 }}</ref> and high beam<ref>{{Cite web|url=http://www.legimonaco.mc/305/legismclois.nsf/Code/8D3FC42532ACB529C125773F002D89B2!OpenDocument|title=LégiMonaco - Code De La Route - Article 75|date=3 March 2016|archive-url=https://web.archive.org/web/20160303214939/http://www.legimonaco.mc/305/legismclois.nsf/Code/8D3FC42532ACB529C125773F002D89B2!OpenDocument |archive-date=3 March 2016 }}</ref> headlamps, and fog lamps if present.<ref>{{Cite web|url=https://www.legimonaco.mc/305/legismclois.nsf/Code/E048DCA0A9119957C125773F002D8B5E!OpenDocument|title=LégiMonaco - Code De La Route - Article 84|date=20 January 2021|archive-url=https://web.archive.org/web/20210120031600/https://www.legimonaco.mc/305/legismclois.nsf/Code/E048DCA0A9119957C125773F002D8B5E!OpenDocument |archive-date=20 January 2021 }}</ref>

In France, a statute passed in November 1936 based on advice from the Central Commission for Automobiles and for Traffic in General, required selective yellow headlights to be fitted.<ref>{{Cite web|url=https://gallica.bnf.fr/ark:/12148/bpt6k65489960|title=Journal officiel de la République française. Lois et décrets|date=5 November 1936|website=Gallica}}</ref> The mandate for yellow headlamps was enacted to reduce driver fatigue from [[Glare (vision)|discomfort glare]].<ref>{{cite journal |last1=Nelson |first1=J. H. |title=Automobile Headlamps |journal=Lighting Research and Technology |date=1 June 1957 |volume=22 |issue=6 IEStrans |pages=141–163 |doi=10.1177/147715355702200601 |bibcode=2014LR&T...46...20S |s2cid=112037485 }}</ref> The requirement initially applied to vehicles registered for road use after April 1937, but was intended to extend to all vehicles through retrofitting of selective yellow lights on older vehicles, from the start of 1939. Later stages of the implementation were disrupted in September 1939 by the outbreak of [[World War II|war]].{{Citation needed|date=November 2014}}

The French yellow-light mandate was based on observations by the [[French Academy of Sciences]] in 1934, when the academy recorded that the selective yellow light was less dazzling than white light and that the light diffused less in fog than green or blue lights.{{Citation needed|date=November 2014}} Yellow light was obtained by dint of yellow glass for the headlight bulb or lens, a yellow coating on a colourless bulb, lens, or reflector, or a yellow filter between the bulb and the lens.<ref>{{cite report |last1=Moore |first1=David W. |title=Headlamp History and Harmonization |publisher=Transportation Research Institute |date=June 1998|hdl=2027.42/49367 |hdl-access=free}}</ref> Filtration losses reduced the emitted light intensity by about 18 percent, which might have contributed to the reduced glare.<ref>{{cite journal|last=Jehu |first=V. J. |title=A comparison of yellow and white headlamp beams |journal=Light and Lighting |volume=47 |pages=287–291 |year=1954}}</ref>

The mandate was in effect until December 1992,<ref name="hearings-1993">{{cite book |author=United States Congress Senate Committee on Appropriations Subcommittee on Transportation and Related Agencies |title=Department of Transportation and Related Agencies Appropriations for Fiscal Year 1993: Hearings Before a Subcommittee of the Committee on Appropriations, United States Senate, One Hundred Second Congress, Second Session, on H.R. 5518 |year=1992 |publisher=U.S. Government Printing Office |isbn=9780160390456 |page=516 |url= https://books.google.com/books?id=HSoW4KdPMB4C&q=Headlamps+in+France+must+provide+yellow+light+while+white+is+required+in+every+other+country+in+Europe.+The+latter+situation+will+change+in+January+1993,+when+white+will+be+allowed+in+France+as+a+result+of+the+integration+of+the+European+Community |access-date=7 August 2018}}</ref> so for many years yellow headlights visually marked French-registered cars wherever they were seen,<ref name="CountryLife">{{cite journal |title=Rallying to the Call |journal=Country Life |date=May 1992 |page=98 |url= https://books.google.com/books?id=tD08AAAAMAAJ&q=Yellow+headlights,+for+many+years+the+sure+sign+of+a+French-registered+car,+are+to+be+phased+out,+following+a+decision+to+standardise+regulations+for+cars+sold+in+the+EC |access-date=7 August 2018}}</ref> though some French drivers are said to have switched to white headlamps despite the requirement for yellow ones.<ref>{{cite book |title=Official Journal of the European Communities: Information and notices, Volume 27 |year=1984 |publisher=Office for Official Publications of the European Communities |url= https://books.google.com/books?id=aGYNAQAAMAAJ&q=The+car+was+equipped+with+the+obligatory+yellow+headlights,+although+more+and+more+French+drivers+are+switching+to+clear+lights,+in+breach+of+the+regulations |access-date=7 August 2018}}</ref>

The requirement was criticised as a [[trade barrier]] in the automobile sector;<ref>{{cite book |last1=Maloney |first1=William A. |last2=McLaughlin |first2=Andrew |title=The European Automobile Industry: Multi Level Governance, Policy and Politics |year=2005 |publisher=Routledge |isbn=9781134829262 |page=183 |url= https://books.google.com/books?id=VKuIAgAAQBAJ&q=French+trade+yellow+headlamps&pg=PA183 |access-date=7 August 2018}}</ref> French politician [[Jean-Claude Martinez]] described it as a [[Protectionism|protectionist law]].<ref>{{cite journal |title=Europe |journal=International Trade Reporter |year=2008 |volume=25 |issue=9 |page=302 |url= https://books.google.com/books?id=U8FEAQAAIAAJ&q=French+lawmaker+Jean-+Claude+Martinez+cited+his+country%27s+long-held+protectionist+rule+that+automobile+headlamps+must+project+a+yellow+beam |access-date=6 August 2018}}</ref>

Formal research found, at best, a small improvement in visual acuity with yellow rather than white headlights,<ref name="LR156"/><ref name="SWOV1976"/> and French automaker [[Peugeot]] estimated that white headlamps produce 20 to 30 percent more light—though without explaining why this estimate was larger than the 15% to 18% value measured in formal research—and wanted drivers of their cars to get the benefits of extra illumination.<ref>{{cite news |title=Science and Technology |newspaper=The Economist |year=1992 |volume=322 |page=86 |url= https://books.google.com/books?id=6_LtAAAAMAAJ&q=French+car+maker,+thinks+that+white+ones+produce+20-30%25+more+light,+and+wants+its+drivers+to+get+the+benefits+that |access-date=7 August 2018}}</ref> More generally, country-specific vehicle technical regulations in Europe were regarded as a costly nuisance. In a survey published in 1988, automakers gave a range of responses when asked what it cost to supply a car with yellow headlamps for France. [[General Motors]] and [[Lotus Cars|Lotus]] said there was no additional cost, [[Rover Company|Rover]] said the additional cost was marginal, and [[Volkswagen]] said yellow headlamps added 28 [[Deutsche Mark]]s to the cost of vehicle production.<ref>{{cite book |title=Research on the "Cost of Non-Europe": The EC 92 automobile sector |volume=11 |year=1988 |publisher=Office for Official Publications of the European Communities |pages=12, 54, 310–333 |author=Ludvigsen Associates |url= http://aei.pitt.edu/47981/1/A9319.pdf |access-date=8 August 2018}}</ref> Addressing the French requirement for yellow lights (among other country-specific lighting requirements) was undertaken as part of an effort toward common vehicle technical standards throughout the [[European Communities|European Community]].<ref name="hearings-1993"/><ref name="CountryLife"/> A provision in [[Council of the European Union|EU Council]] [[Directive (European Union)|Directive]] 91/663, issued on 10 December 1991, specified white headlamps for all new vehicle type-approvals granted by the EC after 1 January 1993 and stipulated that from that date EC (later EU) member states would not be permitted to refuse entry of a vehicle meeting the lighting standards contained in the amended document<ref name="EC91663">{{cite book |title=Commission Directive of 10 December 1991 adapting to technical progress Council Directive 76/756/EEC relating to the installation of lighting and light-signalling devices on motor vehicles and their trailers |year=1991 |url= https://eur-lex.europa.eu/legal-content/EN/TXT/PDF/?uri=CELEX:31991L0663&from=en |access-date=8 August 2018}}</ref>—so France would no longer be able to refuse entry to a vehicle with white headlights. The directive was adopted unanimously by the council, and hence with France's vote.<ref name="Schoutheete">{{cite book |last=Schoutheete |first=Philippe de |title=The Case for Europe: Unity, Diversity, and Democracy in the European Union |year=2000 |publisher=Lynne Rienner Publishers |isbn=9781555879006 |page=47 |url= https://books.google.com/books?id=1XyHxCCcZ-YC&q=White+headlamps+compulsory+for+vehicles+first+registered+1993+at+request+of+French+car+manufacturers&pg=PA47 |access-date=19 July 2018}}</ref>

Though no longer required in France, selective yellow headlamps remain legal there; the current regulation stipulates that "every motor vehicle must be equipped, at the front, with two or four lights, creating in a forward direction selective yellow or white light permitting efficient illumination of the road at night for a distance, in clear conditions, of 100 metres".<ref>{{cite web |title=Section 1: Eclairage et signalisation des véhicules |url= https://www.legifrance.gouv.fr/affichCode.do;jsessionid=D751DF10CDEFA64A4B3DF1EB08E113FE.tpdjo06v_3?idSectionTA=LEGISCTA000006177087&cidTexte=LEGITEXT000006074228&dateTexte=20150101 |website=legifrance.gouv.fr |publisher=Code de la route. Legifrance |language=fr |access-date=7 August 2018}}</ref>