Editing Headlamp (section)

=== Design and style ===
Beyond the engineering, performance, and regulatory-compliance aspects of headlamps, there is the consideration of the various ways they are designed and arranged on a motor vehicle. Headlamps were round for many years because that is the native shape of a [[parabolic reflector]]. Using principles of reflection, the simple symmetric round reflective surface projects light and helps focus the beam.<ref>{{cite web |title=Content - The reflection property of the parabola |url= https://amsi.org.au/ESA_Senior_Years/SeniorTopic2/2a/2a_2content_13.html |website=amsi.org.au |access-date=6 October 2019}}</ref>

==== Headlamp styling outside the United States, pre-1983 ====
[[File:Citroen Headlamps - Euro vs US.jpg|thumb|upright|European (top) and US (bottom) headlamp configurations on a [[Citroën DS]]]]
[[File:Phare ami.jpg|thumb|left|Rectangular headlamp with [[Selective yellow]] bulb on [[Citroën Ami|Citroën Ami 6]]]]

There was no requirement in Europe for headlamps of standardized size or shape, and lamps could be designed in any shape and size, as long as the lamps met the engineering and performance requirements contained in the applicable European [[ECE Regulations|safety standards]]. Rectangular headlamps were first used in 1960, developed by [[Hella (company)|Hella]] for the German [[Ford Taunus P3]] and by [[Cibié]] for the [[Citroën Ami|Citroën Ami 6]]. They were [[Trade restriction|prohibited]] in the United States where round lamps were required until 1975.<ref name="HeadlampHist"/> Another early headlamp styling concept involved conventional round lamps faired into the car's bodywork with aerodynamic glass covers, such as those on the 1961 [[Jaguar E-Type]], and on pre-1967 [[VW Beetle]]s.<ref name="ridelust.com">{{cite web |url= http://www.ridelust.com/illuminating-a-brief-history-of-the-headlight/ |title=Illuminating! A Brief History of the Headlight |access-date=25 January 2019 |archive-url= https://web.archive.org/web/20171201192155/http://www.ridelust.com/illuminating-a-brief-history-of-the-headlight/ |archive-date=1 December 2017 |url-status=dead}}</ref>

==== Headlamp styling in the United States, 1940&ndash;1983 ====
[[File:1949 Nash 600 Super two-door Airflyte at 2015 Macungie show 01 (cropped)left headlamp and turning signal.jpg|thumb|upright|U.S. standard 7-inch headlamp combining low and high beam with turn signal lights below on a 1949 [[Nash 600]]]]
[[File:1965 Chrysler 300 (14754183459).jpg|thumb|Glass-covered 5¾" sealed beam headlamps on a 1965 [[Chrysler 300 non-letter series|Chrysler 300]]]]
[[File:1979 AMC Concord DL coupe silver 2021 AMO at Rambler Ranch 3of6.jpg|thumb|Rectangular sealed-beam headlamps with turn signal light below on a 1979 [[AMC Concord]]]]

Headlight design in the U.S. changed very little from 1940 to 1983.<ref name="HeadlampHist"/><ref name="ridelust.com"/>

In 1940, a consortium of state motor vehicle administrators standardized upon a system of two {{convert|7|in|mm|0|abbr=on}} round [[sealed beam]] headlamps on all vehicles—the only system allowed for 17 years. This requirement eliminated problems of tarnished reflectors by sealing them together with the bulbs.<ref name="Rosenberg">{{cite web |last1=Rosenberg |first1=Diego |title=These 5 cars had quad headlights before they were in vogue |url= https://www.hagerty.com/media/lists/5-cars-had-quad-headlights-before-in-vogue/ |publisher=Hagerty |access-date=27 July 2021 |date=1 May 2020}}</ref> It also made aiming the headlight beams simpler and eliminated non-standard bulbs and lamps.<ref name="Rosenberg"/>

The [[Tucker 48]] included a defining "cyclops-eye" feature: a third center-mounted headlight connected to the car's steering mechanism.<ref>{{cite web |title=How Tucker Cars Work |date=13 June 2007 |website=HowStuffWorks.com |url= https://auto.howstuffworks.com/tucker-cars.htm |access-date=15 March 2019}}</ref> It illuminated only if the steering was moved more than ten degrees off center and the high beams were turned on.<ref>{{cite book |last1=Lehto |first1=Steve |last2=Leno |first2=Jay |title=Preston Tucker and His Battle to Build the Car of Tomorrow |year=2016 |publisher=Chicago Review Press |isbn=9781613749562 |url= https://books.google.com/books?id=f1A9DAAAQBAJ&q=Tucker+48+center+headlamp&pg=PT97 |access-date=15 March 2019}}</ref>

A system of four round lamps, rather than two, one high/low and one high-beam {{convert|5+3/4|in|mm|0|abbr=on}} sealed beam on each side of the vehicle, was introduced on some 1957 Cadillac, Chrysler, DeSoto, and Nash models in states that permitted the new system.<ref name="Rosenberg"/> Separate low and high beam lamps eliminated the need for compromise in lens design and filament positioning required in a single unit.<ref>{{cite journal |last=Olson |first=Paul L. |journal=UMTRI|title=The relative merits of different low beam headlighting systems - a review of the literature. Final report |publisher=Highway Safety Research Institute |date=19 December 1977|hdl=2027.42/669 }}</ref> Other cars followed suit when all states permitted the new lamps by the time the 1958 [[Model year|models]] were brought to market. The four-lamp system permitted more design flexibility and improved low and high beam performance.<ref>{{cite journal |last1=Mead|first1=Howard|last2=Roper|first2=Val J.|date=October 1956|title=New 4-Lamp Dual Sealed-Beam Roadlighting System|journal=SAE Journal|pages=52–59}}</ref><ref>{{cite magazine |last=Rowsome|first=Frank Jr.|date=August 1956|pages=65–69|title=Why Cars are Going to Four Headlights|url= https://books.google.com/books?id=iSUDAAAAMBAJ&pg=PA65|magazine=Popular Science|access-date=14 March 2019}}</ref><ref>{{cite book |author=General Motors Research Laboratories in collaboration with lighting engineers of Guide Lamp Division|title=Optics and Wheels: a story of lighting from the primitive torch to the sealed beam headlamp|publisher=General Motors Public Relations Staff|pages=23–25|year=1965}}</ref> Auto stylists, such as [[Virgil Exner]], carried out design studies with the low beams in their conventional outboard location, and the high beams vertically stacked at the centerline of the car, but no such designs reached volume production.

An example arrangement includes the stacking of two headlamps on each side, with low beams above high beams. The [[Nash Ambassador]] used this arrangement in the 1957 model year.<ref>{{cite web |last=Forkum |first=Allen |title=1957 Nash Ambassador |url= http://www.automotivereport.net/rear-view/1957-nash-ambassador/ |website=AutoGraphic's Automotive Report |access-date=15 March 2019 |date=1 October 2018}}</ref> [[Pontiac (automobile)|Pontiac]] used this design starting in the 1963 model year; [[American Motors]], [[Ford Motor Company|Ford]], [[Cadillac]], and [[Chrysler]] followed two years later. Also in the 1965 model year, the [[Buick Riviera]] had concealable stacked headlamps. Various [[Mercedes-Benz|Mercedes]] models sold in America used this arrangement because their home-market replaceable-bulb headlamps were illegal in the US.

In the late 1950s and early 1960s, some [[Lincoln (automobile)|Lincoln]], [[Buick]], and [[Chrysler]] cars had the headlamps arranged diagonally with the low-beam lamps outboard and above the high-beam lamps. British cars, including the [[Gordon-Keeble]], [[Jensen CV8]], [[Triumph Vitesse]], and [[Bentley S3 Continental]], used such an arrangement as well.<ref>World Car Catalog</ref>

In 1968, the newly initiated [[Federal Motor Vehicle Safety Standard 108]] required all vehicles to have either the twin or quad round sealed beam headlamp system and prohibited any decorative or protective element in front of an operating headlamp. Glass-covered headlamps like those used on the [[Jaguar E-Type]], pre-1968 [[VW Beetle]], 1965 [[Chrysler]] and [[Imperial (automobile)|Imperial]] models, [[Porsche 356]], [[Citroën DS]], and [[Ferrari Daytona]] were no longer permitted, and vehicles had to be equipped with uncovered headlamps for the US market. This made it difficult for vehicles with headlamp configurations designed for good [[aerodynamic]] performance to achieve it in their US-market configurations.

The [[Federal Motor Vehicle Safety Standard 108|FMVSS 108]] was amended in 1974 to permit [[rectangle|rectangular]] sealed-beam headlamps. This allowed manufacturers flexibility to lower the hoods on new cars.<ref>{{cite book |last1=Hollembeak |first1=Barry |title=Today's Technician: Automotive Electricity and Electronics |date=2010 |publisher=Cengage Learning |isbn=9781111784645 |page=210 |url= https://books.google.com/books?id=YR0FAAAAQBAJ&q=Introduction+of+rectangular+headlight+in+1975+enabled+manufacturers+to+lower+the+hood+line&pg=PA210 |access-date=27 July 2021}}</ref> These could be placed in horizontal arrays or in vertically stacked pairs. As previously with round lamps, the US permitted only two standardized sizes of rectangular sealed-beam lamp: A system of two {{convert|200|by|142|mm|in|1|abbr=on}} high/low beam units corresponding to the existing 7-inch round format, or a system of four {{convert|165|by|100|mm|in|1|abbr=on}} units, two high/low and two high-beam. corresponding to the existing {{convert|5+3/4|in|mm|0|abbr=on}} round format.

The rectangular headlamp design became so prevalent in U.S.-made cars that only a few models continued using round headlamps by 1979.<ref>{{cite web |last1=Appel |first1=Tom |title=Bucking a Trend: The Round-Headlamp Cars of 1979 |url= https://blog.consumerguide.com/round-headlamp-cars-of-1979/ |publisher=The Daily Drive - Consumer Guide |access-date=27 July 2021 |date=5 September 2017}}</ref>

==== International headlamp styling, 1983&ndash;present ====
In 1983, granting a 1981 petition from Ford Motor Company, the [[National Highway Traffic Safety Administration#Aerodynamics brings change to NHTSA|US headlamp regulations were amended]] to allow replaceable-bulb, nonstandard-shape, architectural headlamps with aerodynamic lenses that could for the first time be made of hard-coated [[polycarbonate]]. This allowed the first US-market car since 1939 with replaceable bulb headlamps: the 1984 [[Lincoln Mark VII]]. These composite headlamps were sometimes referred to as "Euro" headlamps since aerodynamic headlamps were common in Europe. Though conceptually similar to European headlamps with non-standardized shape and replaceable-bulb construction, these headlamps conform to the headlamp design, construction, and performance specifications of US [[Federal Motor Vehicle Safety Standard 108]] rather than the internationalized European [[World Forum for Harmonization of Vehicle Regulations|safety standards]] used outside North America. Nevertheless, this change to US regulations made it possible for headlamp styling in the US market to move closer to that in Europe.

==== Hidden headlamps ====
{{Main|Hidden headlamps}}
[[File:Mazda323FBG KlappscheinwerferAni.gif|thumb|right|Pop-up headlamps on a [[Mazda Familia Astina|Mazda 323F]]]]

Hidden headlamps were introduced in 1936,<ref name=Slate2013>{{cite web|title=Whatever Happened to Pop-Up Headlights?|url=http://www.slate.com/blogs/the_eye/2013/10/22/pop_up_headlights_why_the_hidden_headlamp_has_disappeared.html|website=Slate|access-date=4 January 2015|date=22 October 2013}}</ref> on the [[Cord 810/812]]. They were mounted in the front fenders, which were smooth until the lights were cranked out—each with its own small dash-mounted crank—by the operator. They aided [[aerodynamics]] when the headlamps were not in use and were among the Cord's signature design features.

Later hidden headlamps require one or more vacuum-operated [[Servomechanism|servos]] and reservoirs, with associated plumbing and linkage, or electric [[Electric motor|motors]], [[gear]]trains and linkages to raise the lamps to an exact position to assure correct aiming despite ice, snow, and age. Some hidden headlamp designs, such as those on the [[Saab Sonett]] III, used a lever-operated mechanical linkage to raise the headlamps into position.

During the 1960s and 1970s, many notable sports cars used this feature such as the [[Chevrolet Corvette (C3)]], [[Ferrari Berlinetta Boxer]] and [[Lamborghini Countach]] as they allowed low bonnet lines but raised the lights to the required height, but since 2004 no modern volume-produced car models use hidden headlamps because they present difficulties in complying with pedestrian-protection provisions added to [[World Forum for Harmonization of Vehicle Regulations|international auto safety regulations]] regarding protuberances on car bodies to minimize injury to pedestrians struck by cars.<ref name=Slate2013/>

Some hidden headlamps themselves do not move, but rather are covered when not in use by panels designed to blend in with the car's styling. When the lamps are switched on, the covers are swung out of the way, usually downward or upward, for example on the 1992 [[Jaguar XJ220]]. The door mechanism may be actuated by [[manifold vacuum|vacuum]] pots, as on some [[Ford Motor Company|Ford]] vehicles of the late 1960s through early 1980s such as the 1967–1970 [[Mercury Cougar]], or by an electric motor as on various Chrysler products of the middle 1960s through late 1970s such as the 1966–1967 [[Dodge Charger (B-body)|Dodge Charger]].