Editing Headlamp (section)

==== 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>