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A headlamp is a
lamp Lamp, Lamps or LAMP may refer to: Lighting * Oil lamp, using an oil-based fuel source * Kerosene lamp, using kerosene as a fuel * Electric lamp, or light bulb, a replaceable component that produces light from electricity * Light fixture, or ligh ...
attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise
usage The usage of a language is the ways in which its written and spoken variations are routinely employed by its speakers; that is, it refers to "the collective habits of a language's native speakers", as opposed to idealized models of how a languag ...
, ''headlamp'' is the term for the device itself and ''headlight'' is the term for the
beam of light ''Beam of Light'' is the second full-length album by the Japanese rock band One Ok Rock, released on May 28, 2008. It reached No. 17 on the Oricon weekly chart, and charted for six weeks before it dropped out. Track listing Notes * "Abducti ...
produced and distributed by the device. Headlamp performance has steadily improved throughout the automobile age, spurred by the great disparity between daytime and nighttime traffic fatalities: the US
National Highway Traffic Safety Administration The National Highway Traffic Safety Administration (NHTSA ) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" relat ...
states that nearly half of all traffic-related fatalities occur in the dark, despite only 25% of traffic travelling during darkness. Other vehicles, such as trains and aircraft, are required to have headlamps. Bicycle headlamps are often used on bicycles, and are required in some jurisdictions. They can be powered by a
battery Battery most often refers to: * Electric battery, a device that provides electrical power * Battery (crime), a crime involving unlawful physical contact Battery may also refer to: Energy source *Automotive battery, a device to provide power t ...
or a small generator like a
bottle A bottle is a narrow-necked container made of an impermeable material (such as glass, plastic or aluminium) in various shapes and sizes that stores and transports liquids. Its mouth, at the bottling line, can be sealed with an internal s ...
or hub dynamo.


History of automotive headlamps


Origins

The first horseless carriages used carriage lamps, which proved unsuitable for travel at speed. The earliest lights used candles as the most common type of fuel.


Mechanics


Gas headlamp

The earliest headlamps, fuelled by combustible gas such as
acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
gas or oil, operated from the late 1880s. Acetylene gas lamps were popular in 1900s because the flame is resistant to wind and rain. Thick concave mirrors combined with magnifying lenses projected the acetylene flame light. A number of car manufacturers offered Prest-O-Lite ''calcium carbide acetylene gas generator cylinder'' with gas feed pipes for lights as standard equipment for 1904 cars.


Electric headlamp

The first electric headlamps were introduced in 1898 on the Columbia Electric Car from the Electric Vehicle Company of Hartford,
Connecticut Connecticut () is the southernmost state in the New England region of the Northeastern United States. It is bordered by Rhode Island to the east, Massachusetts to the north, New York (state), New York to the west, and Long Island Sound to the ...
, and were optional. Two factors limited the widespread use of electric headlamps: the short life of filaments in the harsh automotive environment, and the difficulty of producing dynamos small enough, yet powerful enough to produce sufficient current.
Peerless Peerless may refer to: Companies and organizations * Peerless Motor Company, an American automobile manufacturer. * Peerless Brewing Company, in Birkenhead, UK * Peerless Group, an insurance and financial services company in India * Peerless Re ...
made electric headlamps standard in 1908. A Birmingham, England firm called Pockley Automobile Electric Lighting Syndicate marketed the world's first electric car-lights as a complete set in 1908, which consisted of headlamps, sidelamps, and tail lights that were powered by an eight-volt battery. In 1912
Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed ...
integrated their vehicle's Delco electrical ignition and lighting system, forming the modern vehicle electrical system. The Guide Lamp Company introduced "dipping" (low-beam) headlamps in 1915, but the 1917 Cadillac system allowed the light to be dipped using a lever inside the car rather than requiring the driver to stop and get out. The 1924 Bilux bulb was the first modern unit, having the light for both low (dipped) and high (main) beams of a headlamp emitting from a single bulb. A similar design was introduced in 1925 by Guide Lamp called the "Duplo". In 1927 the foot-operated dimmer switch or dip switch was introduced and became standard for much of the century. 1933–1934 Packards featured tri-beam headlamps, the bulbs having three filaments. From highest to lowest, the beams were called "country passing", "country driving" and "city driving". The 1934 Nash also used a three-beam system, although in this case with bulbs of the conventional two-filament type, and the intermediate beam combined low beam on the driver's side with high beam on the passenger's side, so as to maximise the view of the roadside while minimizing glare toward oncoming traffic. The last vehicles with a foot-operated dimmer switch were the 1991
Ford F-Series The Ford F-Series is a series of light-duty trucks marketed and manufactured by Ford since the 1948 model year. Slotted above the Ford Ranger in the Ford truck model range, the F-Series is marketed as a range of full-sized pickup trucks. ...
and E-Series conolinevans. Fog lamps were new for 1938 Cadillacs, and their 1954 "Autronic Eye" system automated the selection of high and low beams. Directional lighting, using a switch and electromagnetically shifted reflector to illuminate the curbside only, was introduced in the rare, one-year-only 1935 Tatra. Steering-linked lighting was featured on the 1947 Tucker Torpedo's center-mounted headlight and was later popularized by the Citroën DS. This made it possible to turn the light in the direction of travel when the steering wheel turned. The standardized round sealed-beam headlamp, one per side, was required for all vehicles sold in the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...
from 1940, virtually freezing usable lighting technology in place until the 1970s for Americans. In 1957 the law changed to allow smaller round sealed beams, two per side of the vehicle, and in 1974
rectangular In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a parallelogram containin ...
sealed beams were permitted as well. Britain, Australia, and some other
Commonwealth A commonwealth is a traditional English term for a political community founded for the common good. Historically, it has been synonymous with "republic". The noun "commonwealth", meaning "public welfare, general good or advantage", dates from the ...
countries, as well as Japan and
Sweden Sweden, formally the Kingdom of Sweden,The United Nations Group of Experts on Geographical Names states that the country's formal name is the Kingdom of SwedenUNGEGN World Geographical Names, Sweden./ref> is a Nordic countries, Nordic c ...
, also made extensive use of 7-inch sealed beams, though they were not mandated as they were in the United States. This headlamp format was not widely accepted in continental Europe, which found replaceable bulbs and variations in the size and shape of headlamps useful in car design. Technology moved forward in the rest of the world. In 1962 a European consortium of bulb- and headlamp-makers introduced the first
halogen lamp A halogen lamp (also called tungsten halogen, quartz-halogen, and quartz iodine lamp) is an incandescent lamp consisting of a tungsten filament sealed in a compact transparent envelope that is filled with a mixture of an inert gas and a small ...
for vehicle headlamp use, the H1. Shortly thereafter headlamps using the new light source were introduced in Europe. These were effectively prohibited in the US, where standard-size sealed beam headlamps were mandatory and intensity regulations were low. US lawmakers faced pressure to act, due both to lighting effectiveness and to vehicle aerodynamics/fuel savings. High-beam peak intensity, capped at 140,000 candela per side of the car in Europe, was limited in the United States to 37,500 candela on each side of the car until 1978, when the limit was raised to 75,000. An increase in high-beam intensity to take advantage of the higher allowance could not be achieved without a move to halogen technology, and so sealed- beam headlamps with internal halogen lamps became available for use on 1979 models in the United States.
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
sealed beams dominate the sealed-beam market, which has declined steeply since replaceable-
bulb In botany, a bulb is structurally a short stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs dur ...
headlamps were permitted in 1983. High-intensity discharge (HID) systems appeared in the early 1990s, first in the
BMW 7 Series The BMW 7 Series is a full-size luxury sedan manufactured and marketed by the German automaker BMW since 1977. It is the successor to the BMW E3 "New Six" sedan and is now in its seventh generation. The 7 Series is BMW's flagship car and is ...
. 1996's Lincoln Mark VIII was an early American effort at HIDs, and was the only car with DC HIDs.


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 A parabolic (or paraboloid or paraboloidal) reflector (or dish or mirror) is a reflective surface used to collect or project energy such as light, sound, or radio waves. Its shape is part of a circular paraboloid, that is, the surface genera ...
. Using principles of reflection, the simple symmetric round reflective surface projects light and helps focus the beam.


Headlamp styling outside the United States, pre-1983

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
safety standards Safety standards are standards designed to ensure the safety of products, activities and processes, etc. They may be advisory or compulsory and are normally laid down by an advisory or regulatory body that may be either voluntary or statutory. In ...
. Rectangular headlamps were first used in 1960, developed by
Hella ''Hella'' is an American slang term that originated in the San Francisco Bay Area. It is used as an intensifying adverb such as in "hella bad" or "hella good" and was eventually added to the '' Oxford English Dictionary'' in 2002. It is possib ...
for the German Ford Taunus P3 and by
Cibié Valeo is a French global automotive supplier headquartered in France, listed on the Paris Stock Exchange ( CAC-40 Index). It supplies a wide range of products to automakers and the aftermarket. The Group employs 113,600 people in 33 countries w ...
for the Citroën Ami 6. They were prohibited in the United States where round lamps were required until 1975. 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 The Jaguar E-Type, or the Jaguar XK-E for the North American market, is a British sports car that was manufactured by Jaguar Cars Ltd between 1961 and 1974. Its combination of beauty, high performance, and competitive pricing established the m ...
, and on pre-1967 VW Beetles.


Headlamp styling in the United States, 1940–1983

Headlight design in the U.S. changed very little from 1940 to 1983. In 1940, a consortium of state motor vehicle administrators standardized upon a system of two 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. It also made aiming the headlight beams simpler and eliminated non-standard bulbs and lamps. The Tucker 48 included a defining "cyclops-eye" feature: a third center-mounted headlight connected to the car's steering mechanism. It only illuminated if the steering was moved more than ten degrees off center and the high beams were turned on. A system of four round lamps, rather than two, one high/low and one high-beam 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. Separate low and high beam lamps eliminated the need for compromise in lens design and filament positioning required in a single unit. Other cars followed suit when all states permitted the new lamps by the time the 1958
models A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a measure. Models c ...
were brought to market. The four-lamp system permitted more design flexibility and improved low and high beam performance. 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 The Nash Ambassador is a luxury automobile that was produced by Nash Motors from 1927 until 1957. For the first five years it was a top trim level, then from 1932 on a standalone model. Ambassadors were lavishly equipped and beautifully construc ...
used this arrangement in the 1957 model year.
Pontiac Pontiac may refer to: *Pontiac (automobile), a car brand *Pontiac (Ottawa leader) ( – 1769), a Native American war chief Places and jurisdictions Canada *Pontiac, Quebec, a municipality ** Apostolic Vicariate of Pontiac, now the Roman Catholic D ...
used this design starting in the 1963 model year; American Motors, Ford,
Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed ...
, and
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
followed two years later. Also in the 1965 model year, the Buick Riviera had concealable stacked headlamps. Various 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,
Buick Buick () is a division of the American automobile manufacturer General Motors (GM). Started by automotive pioneer David Dunbar Buick in 1899, it was among the first American marques of automobiles, and was the company that established General ...
, and
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
cars had the headlamps arranged diagonally with the low-beam lamps outboard and above the high-beam lamps. British cars including the
Gordon-Keeble Gordon-Keeble was a British car marque, made first in Slough, then Eastleigh, and finally in Southampton (all in England), between 1964 and 1967. The marque's badge was unusual in featuring a tortoise — a pet tortoise walked into the frame ...
,
Jensen CV8 The Jensen C-V8 is a four-seater GT car produced by Jensen Motors between 1962 and 1966. Launched in October 1962, the C-V8 series had fibreglass bodywork with aluminium door skins, as did the preceding 541 series. All C-V8s used big-block eng ...
, Triumph Vitesse, and Bentley S3 Continental used such an arrangement as well. In 1968, the newly initiated
Federal Motor Vehicle Safety Standard 108 Federal Motor Vehicle Safety Standard 108 (FMVSS 108) regulates all automotive lighting, signalling and reflective devices in the United States. Like all other Federal Motor Vehicle Safety Standards, FMVSS 108 is administered by the United States ...
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 The Jaguar E-Type, or the Jaguar XK-E for the North American market, is a British sports car that was manufactured by Jaguar Cars Ltd between 1961 and 1974. Its combination of beauty, high performance, and competitive pricing established the m ...
, pre-1968 VW Beetle, 1965
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
and
Imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas ...
models,
Porsche 356 The Porsche 356 is a sports car that was first produced by Austrian company Porsche Salzburg, Porsche Konstruktionen GesmbH (1948–1949), and then by German company Porsche, Dr. Ing. h. c. F. Porsche GmbH (1950–1965). It was Porsche's first ...
, 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 Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dyn ...
performance to achieve it in their US-market configurations. The FMVSS 108 was amended in 1974 to permit
rectangular In Euclidean plane geometry, a rectangle is a quadrilateral with four right angles. It can also be defined as: an equiangular quadrilateral, since equiangular means that all of its angles are equal (360°/4 = 90°); or a parallelogram containin ...
sealed-beam headlamps. This allowed manufacturers flexibility to lower the hoods on new cars. 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 high/low beam units corresponding to the existing 7-inch round format, or a system of four units, two high/low and two high-beam. corresponding to the existing 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.


International headlamp styling, 1983–present

In 1983, granting a 1981 petition from Ford Motor Company, the 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 Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
. 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 Federal Motor Vehicle Safety Standard 108 (FMVSS 108) regulates all automotive lighting, signalling and reflective devices in the United States. Like all other Federal Motor Vehicle Safety Standards, FMVSS 108 is administered by the United States ...
rather than the internationalized European
safety standards Safety standards are standards designed to ensure the safety of products, activities and processes, etc. They may be advisory or compulsory and are normally laid down by an advisory or regulatory body that may be either voluntary or statutory. In ...
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

Hidden headlamps were introduced in 1936, 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 Aerodynamics, from grc, ἀήρ ''aero'' (air) + grc, δυναμική (dynamics), is the study of the motion of air, particularly when affected by a solid object, such as an airplane wing. It involves topics covered in the field of fluid dy ...
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 servos and reservoirs, with associated plumbing and linkage, or electric
motors An engine or motor is a machine designed to convert one or more forms of energy into mechanical energy. Available energy sources include potential energy (e.g. energy of the Earth's gravitational field as exploited in hydroelectric power g ...
,
gear A gear is a rotating circular machine part having cut teeth or, in the case of a cogwheel or gearwheel, inserted teeth (called ''cogs''), which mesh with another (compatible) toothed part to transmit (convert) torque and speed. The basic ...
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 international auto safety regulations regarding protuberances on car bodies to minimize injury to pedestrians struck by cars. 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 Jaguar XJ220 is a two-seat sports car produced by British luxury car manufacturer Jaguar from 1992 until 1994, in collaboration with the specialist automotive and race engineering company Tom Walkinshaw Racing. The XJ220 recorded a top ...
. The door mechanism may be actuated by
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
pots, as on some Ford vehicles of the late 1960s through early 1980s such as the 1967–1970
Mercury Cougar Mercury Cougar is a nameplate applied to a diverse series of automobiles sold by the Mercury division of Ford from 1967 to 1997 and from 1999 to 2002. While the nameplate is most commonly associated with two-door coupes, at various times durin ...
, or by an electric motor as on various Chrysler products of the middle 1960s through late 1970s such as the 1966–1967
Dodge Charger The Dodge Charger is a model of automobile marketed by Dodge in various forms over seven generations since 1966. The first Charger was a show car in 1964. A 1965 Charger II concept car resembled the 1966 production version. The Charger has ...
.


Regulations and requirements

Modern headlamps are electrically operated, positioned in pairs, one or two on each side of the front of a vehicle. A headlamp system is required to produce a low and a high beam, which may be produced by multiple pairs of single-beam lamps or by a pair of dual-beam lamps, or a mix of single-beam and dual-beam lamps. High beams cast most of their light straight ahead, maximizing seeing distance but producing too much
glare Glare (derived from GLAss REinforced laminate ) is a fiber metal laminate (FML) composed of several very thin layers of metal (usually aluminum) interspersed with layers of S-2 glass-fiber ''pre-preg'', bonded together with a matrix such as epo ...
for safe use when other vehicles are present on the road. Because there is no special control of upward light, high beams also cause backdazzle from
fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
, rain and snow due to the retroreflection of the water
droplet A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the lower end of a tube or other surface boundary, producing a hanging drop called a pendant ...
s. Low beams have stricter control of upward light, and direct most of their light downward and either rightward (in right-traffic countries) or leftward (in left-traffic countries), to provide forward visibility without excessive glare or backdazzle.


''Low'' beam

Low beam (dipped beam, passing beam, meeting beam) headlamps provide a distribution of light designed to provide forward and lateral illumination, with limits on light directed towards the eyes of other road users to control glare. This beam is intended for use whenever other vehicles are present ahead, whether oncoming or being overtaken. The international ECE Regulations for filament headlamps and for high-intensity discharge headlamps specify a beam with a sharp, asymmetric cutoff preventing significant amounts of light from being cast into the eyes of drivers of preceding or oncoming cars. Control of glare is less strict in the North American
SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Aut ...
beam standard contained in FMVSS / CMVSS 108.


High beam

High beam (main beam, driving beam, full beam) headlamps provide a bright, center-weighted distribution of light with no particular control of light directed towards other road users' eyes. As such, they are only suitable for use when alone on the road, as the glare they produce will dazzle other drivers. International ECE Regulations permit higher-intensity high-beam headlamps than are allowed under North American regulations.


Compatibility with traffic directionality

Most low-beam headlamps are specifically designed for use on only one side of the road. Headlamps for use in left-traffic countries have low-beam headlamps that "dip to the left"; the light is distributed with a downward/leftward bias to show the driver the road and signs ahead without blinding oncoming traffic. Headlamps for right-traffic countries have low beams that "dip to the right", with most of their light directed downward/rightward. Within Europe, when driving a vehicle with right-traffic headlamps in a left-traffic country or vice versa for a limited time (as for example on vacation or in transit), it is a legal requirement to adjust the headlamps temporarily so that their wrong-side beam distribution does not dazzle oncoming drivers. This may be achieved by methods including adhering opaque decals or prismatic lenses to a designated part of the lens. Some projector-type headlamps can be made to produce a proper left- or right-traffic beam by shifting a lever or other movable element in or on the lamp assembly. Many tungsten (pre-halogen) European-code headlamps made in France by Cibié, Marchal, and Ducellier could be adjusted to produce either a left- or a right-traffic low beam by means of a two-position bulb holder. Because wrong-side-of-road headlamps blind oncoming drivers and do not adequately light the driver's way, and blackout strips and adhesive prismatic lenses reduce the safety performance of the headlamps, some countries require all vehicles registered or used on a permanent or semi-permanent basis within the country to be equipped with headlamps designed for the correct traffic-handedness. North American vehicle owners sometimes privately import and install Japanese-market (JDM) headlamps on their car in the mistaken belief that the beam performance will be better, when in fact such misapplication is quite hazardous and illegal.


Adequacy

Vehicle headlamps have been found unable to illuminate an assured clear distance ahead at speeds above 60 km/h (40 mph). Se
California Official Reports: Online Opinions
/ref> It may be unsafe and, in a few areas, illegal to drive above this speed at night.


Use in daytime

Some countries require automobiles to be equipped with
daytime running lights A daytime running lamp (DRL, also daytime running light) is an automotive lighting and bicycle lighting device on the front of a roadgoing motor vehicle or bicycle, automatically switched on when the vehicle's handbrake has been pulled down, w ...
(DRL) to increase the conspicuity of vehicles in motion during the daytime. Regional regulations govern how the DRL function may be provided. In Canada, the DRL function required on vehicles made or imported since 1990 can be provided by the headlamps, the fog lamps, steady-lit operation of the front turn signals, or by special daytime running lamps. Functionally dedicated daytime running lamps not involving the headlamps are required on all new cars first sold in the
European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are located primarily in Europe, Europe. The union has a total area of ...
since February 2011. In addition to the EU and Canada, countries requiring DRL include Albania, Argentina, Bosnia and Herzegovina, Colombia (no more from Aug/2011), Iceland, Israel, Macedonia, Norway, Moldova, Russia, Serbia, and Uruguay.


Construction, performance, and aim

There are two different beam pattern and headlamp construction standards in use in the world: The ECE standard, which is allowed or required in virtually all industrialized countries except the United States, and the
SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Aut ...
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.  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. 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. In North America, the design, performance, and installation of all motor vehicle lighting devices are regulated by Federal and Canada Motor Vehicle Safety Standard 108, which incorporates
SAE SAE or Sae may refer to: Science and technology : * Selective area epitaxy, local growth of epitaxial layer through a patterned dielectric mask deposited on a semiconductor substrate * Serious adverse event, in a clinical trial * Simultaneous Aut ...
technical standards. Elsewhere in the world, ECE 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. In most other countries, and in the US since 1984, replaceable-bulb headlamps predominate. Headlamps must be kept in proper aim. 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.


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. 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

= 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. 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. Researchers note that tungsten filament lamps emit only a small amount of the blue light blocked by a selective-yellow filter, so such filtration makes only a small difference in the characteristics of the light output, 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. Selective yellow headlamps are no longer common, but are permitted in various countries throughout Europe as well as in non-European locales such as South Korea, Japan and New Zealand. In
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, yellow headlamps are allowed and the vehicle regulations in
Monaco Monaco (; ), officially the Principality of Monaco (french: Principauté de Monaco; Ligurian: ; oc, Principat de Mónegue), is a sovereign city-state and microstate on the French Riviera a few kilometres west of the Italian region of Lig ...
still officially require selective yellow light from all vehicles' low beam and high beam headlamps, and fog lamps if present. 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. The mandate for yellow headlamps was enacted to reduce driver fatigue from discomfort glare. 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
war War is an intense armed conflict between states, governments, societies, or paramilitary groups such as mercenaries, insurgents, and militias. It is generally characterized by extreme violence, destruction, and mortality, using regular o ...
. The French yellow-light mandate was based on observations by the
French Academy of Sciences The French Academy of Sciences (French: ''Académie des sciences'') is a learned society, founded in 1666 by Louis XIV at the suggestion of Jean-Baptiste Colbert, to encourage and protect the spirit of French scientific research. It was at ...
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. 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. Filtration losses reduced the emitted light intensity by about 18 percent, which might have contributed to the reduced glare. The mandate was in effect until December 1992, so for many years yellow headlights visually marked French-registered cars wherever they were seen, though some French drivers are said to have switched to white headlamps despite the requirement for yellow ones. The requirement was criticised as a
trade barrier Trade barriers are government-induced restrictions on international trade. According to the theory of comparative advantage, trade barriers are detrimental to the world economy and decrease overall economic efficiency. Most trade barriers work o ...
in the automobile sector; French politician
Jean-Claude Martinez Jean-Claude Martinez (born 30 July 1945, in Sète, Hérault) is a French politician and Member of the European Parliament for the south-west of France. He was a member and a vice-president of the Front National, and was among the '' Non-Inscri ...
described it as a protectionist law. Formal research found, at best, a small improvement in visual acuity with yellow rather than white headlights, and French automaker
Peugeot Peugeot (, , ) is a French brand of automobiles owned by Stellantis. The family business that preceded the current Peugeot companies was founded in 1810, with a steel foundry that soon started making hand tools and kitchen equipment, and then ...
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. 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 The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
and Lotus said there was no additional cost,
Rover Rover may refer to: People * Constance Rover (1910–2005), English historian * Jolanda de Rover (born 1963), Dutch swimmer * Rover Thomas (c. 1920–1998), Indigenous Australian artist Places * Rover, Arkansas, US * Rover, Missouri, US * ...
said the additional cost was marginal, and
Volkswagen Volkswagen (),English: , . abbreviated as VW (), is a German Automotive industry, motor vehicle manufacturer headquartered in Wolfsburg, Lower Saxony, Germany. Founded in 1937 by the German Labour Front under the Nazi Party and revived into a ...
said yellow headlamps added 28
Deutsche Mark The Deutsche Mark (; English: ''German mark''), abbreviated "DM" or "D-Mark" (), was the official currency of West Germany from 1948 until 1990 and later the unified Germany from 1990 until the adoption of the euro in 2002. In English, it was ...
s to the cost of vehicle production. 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 Community The European Economic Community (EEC) was a regional organization created by the Treaty of Rome of 1957,Today the largely rewritten treaty continues in force as the ''Treaty on the functioning of the European Union'', as renamed by the Lis ...
. A provision in EU Council 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—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. 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".


Optical systems


Reflector lamps


Lens optics

A light source (
filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
or arc) is placed at or near the focus of a reflector, which may be parabolic or of non-parabolic complex shape. Fresnel and prism optics moulded into the headlamp lens
refract In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenomeno ...
(shift) parts of the light laterally and vertically to provide the required light distribution pattern. Most sealed-beam headlamps have lens optics.


Reflector optics

Starting in the 1980s, headlamp reflectors began to evolve beyond the simple stamped steel
parabola In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One descri ...
. The 1983 Austin Maestro was the first vehicle equipped with Lucas-Carello's ''homofocal'' reflectors, which comprised parabolic sections of different focal length to improve the efficiency of light collection and distribution.
CAD Computer-aided design (CAD) is the use of computers (or ) to aid in the creation, modification, analysis, or optimization of a design. This software is used to increase the productivity of the designer, improve the quality of design, improve c ...
technology allowed the development of reflector headlamps with nonparabolic, complex-shape reflectors. First commercialised by
Valeo Valeo is a French global automotive supplier headquartered in France, listed on the Paris Stock Exchange ( CAC-40 Index). It supplies a wide range of products to automakers and the aftermarket. The Group employs 113,600 people in 33 countries wo ...
under their Cibié brand, these headlamps would revolutionise automobile design. The 1987 US-market Dodge Monaco/Eagle Premier twins and European
Citroën XM The Citroën XM is a front-engine, front-drive, five-passenger, five-door hatchback noted for its hydropneumatic suspension. Manufactured and marketed by Citroën from 1989 to 2000, with a minor facelift in 1994, XM production reached 333,405 ov ...
were the first cars with complex-reflector headlamps with faceted optic lenses.
General Motors The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
' Guide Lamp division in America had experimented with clear-lens complex-reflector lamps in the early 1970s and achieved promising results, but the US-market 1990
Honda Accord The , also known as the in Japan and China for certain generations, is a series of cars manufactured by Honda since 1976, best known for its four-door sedan variant, which has been one of the best-selling cars in the United States since 1989. ...
was first with clear-lens multi-reflector headlamps; these were developed by Stanley in Japan. The optics to distribute the light in the desired pattern are designed into the reflector itself, rather than into the lens. Depending on the development tools and techniques in use, the reflector may be engineered from the start as a bespoke shape, or it may start as a
parabola In mathematics, a parabola is a plane curve which is mirror-symmetrical and is approximately U-shaped. It fits several superficially different mathematical descriptions, which can all be proved to define exactly the same curves. One descri ...
standing in for the size and shape of the completed package. In the latter case, the entire surface area is modified so as to produce individual segments of specifically calculated, complex contours. The shape of each segment is designed such that their cumulative effect produces the required light distribution pattern. Modern reflectors are commonly made of compression-moulded or injection moulded plastic, though glass and metal optic reflectors also exist. The reflective surface is vapour deposited aluminum, with a clear overcoating to prevent the extremely thin aluminium from oxidizing. Extremely tight tolerances must be maintained in the design and production of complex-reflector headlamps.


= Dual-beam reflector headlamps

= Night driving is difficult and dangerous due to the blinding
glare Glare (derived from GLAss REinforced laminate ) is a fiber metal laminate (FML) composed of several very thin layers of metal (usually aluminum) interspersed with layers of S-2 glass-fiber ''pre-preg'', bonded together with a matrix such as epo ...
of headlights from oncoming traffic. Headlamps that satisfactorily illuminate the road ahead without causing glare have long been sought. The first solutions involved resistance-type dimming circuits, which decreased the intensity of the headlamps. This yielded to tilting reflectors, and later to dual-filament bulbs with a high and a low beam. In a two-filament headlamp, there can only be one filament exactly at the focal point of the reflector. There are two primary means of producing two different beams from a two-filament bulb in a single reflector.


American system

One filament is located at the focal point of the reflector. The other filament is shifted axially and radially away from the focal point. In most 2-filament sealed beams and in 2-filament replaceable bulbs of type 9004, 9007, and H13, the high-beam filament is at the focal point and the low-beam filament is off focus. For use in right-traffic countries, the low-beam filament is positioned slightly upward, forward, and leftward of the focal point, so that when it is energized, the beam is widened and shifted slightly downward and rightward of the headlamp axis. Transverse-filament bulbs such as the 9004 can only be used with the filaments horizontal, but axial-filament bulbs can be rotated or "clocked" by the headlamp designer to optimize the beam pattern or to affect the traffic-handedness of the low beam. The latter is accomplished by clocking the low-beam filament in an upward-forward-leftward position to produce a right-traffic low beam, or in an upward-forward-rightward position to produce a left-traffic low beam. The opposite tactic has also been employed in certain two-filament sealed beams. Placing the low beam filament at the focal point to maximize light collection by the reflector, and positioning the high beam filament slightly rearward-rightward-downward of the focal point. The relative directional shift between the two beams is the same with either technique – in a right-traffic country, the low beam is slightly downward-rightward and the high beam is slightly upward-leftward, relative to one another – but the lens optics must be matched to the filament placements selected.


European system

The traditional European method of achieving low and high beams from a single bulb involves two filaments along the axis of the reflector. The high beam filament is on the focal point, while the low beam filament is approximately 1 cm forward of the focal point and 3 mm above the axis. Below the low beam filament is a cup-shaped shield (called a " Graves shield") spanning an arc of 165°. When the low beam filament is illuminated, this shield casts a shadow on the corresponding lower area of the reflector, blocking downward light rays that would otherwise strike the reflector and be cast above the horizon. The bulb is rotated (or "clocked") within the headlamp to position the Graves shield so as to allow light to strike a 15° wedge of the lower half of the reflector. This is used to create the upsweep or upstep characteristic of ECE low beam light distributions. The bulb's rotative position within the reflector depends on the type of beam pattern to be produced and the traffic directionality of the market for which the headlamp is intended. This system was first used with the tungsten incandescent Bilux/Duplo R2 bulb of 1954, and later with the
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
H4 bulb of 1971. In 1992, US regulations were amended to permit the use of H4 bulbs redesignated HB2 and 9003, and with slightly different production tolerances stipulated. These are physically and electrically interchangeable with H4 bulbs. Similar optical techniques are used, but with different reflector or lens optics to create a US beam pattern rather than a European one. Each system has its advantages and disadvantages. The American system historically permitted a greater overall amount of light within the low beam, since the entire reflector and lens area is used, but at the same time, the American system has traditionally offered much less control over upward light that causes glare, and for that reason has been largely rejected outside the US. In addition, the American system makes it difficult to create markedly different low and high beam light distributions. The high beam is usually a rough copy of the low beam, shifted slightly upward and leftward. The European system traditionally produced low beams containing less overall light, because only 60% of the reflector's surface area is used to create the low beam. However, low beam focus and glare control are easier to achieve. In addition, the lower 40% of the reflector and lens are reserved for high beam formation, which facilitates the optimization of both low and high beams.


Developments in the 1990s and 2000s

Complex-reflector technology in combination with new bulb designs such as H13 is enabling the creation of European-type low and high beam patterns without the use of a Graves Shield, while the 1992 US approval of the H4 bulb has made traditionally European 60% / 40% optical area divisions for low and high beam common in the US. Therefore, the difference in active optical area and overall beam light content no longer necessarily exists between US and ECE beams. Dual-beam HID headlamps employing reflector technology have been made using adaptations of both techniques.


Projector (polyellipsoidal) lamps

In this system a filament is located at one focus of an ellipsoidal reflector and has a condenser
lens A lens is a transmissive optical device which focuses or disperses a light beam by means of refraction. A simple lens consists of a single piece of transparent material, while a compound lens consists of several simple lenses (''elements ...
at the front of the lamp. A shade is located at the image plane, between the reflector and lens, and the projection of the top edge of this shade provides the low-beam cutoff. The shape of the shade edge and its exact position in the optical system determine the shape and sharpness of the cutoff. The shade may be lowered by a
solenoid upright=1.20, An illustration of a solenoid upright=1.20, Magnetic field created by a seven-loop solenoid (cross-sectional view) described using field lines A solenoid () is a type of electromagnet formed by a helix, helical coil of wire whose ...
actuated pivot to provide a low beam, and removed from the light path for the high beam. Such optics are known as ''BiXenon'' or ''BiHalogen'' projectors. If the cutoff shade is fixed in the light path, separate high-beam lamps are required. The condenser lens may have slight fresnel rings or other surface treatments to reduce cutoff sharpness. Modern condenser lenses incorporate optical features specifically designed to direct some light upward towards the locations of retroreflective overhead road signs.
Hella ''Hella'' is an American slang term that originated in the San Francisco Bay Area. It is used as an intensifying adverb such as in "hella bad" or "hella good" and was eventually added to the '' Oxford English Dictionary'' in 2002. It is possib ...
introduced ellipsoidal optics for
acetylene Acetylene ( systematic name: ethyne) is the chemical compound with the formula and structure . It is a hydrocarbon and the simplest alkyne. This colorless gas is widely used as a fuel and a chemical building block. It is unstable in its pure ...
headlamps in 1911, but following the electrification of vehicle lighting, this optical technique wasn't used for many decades. The first modern polyellipsoidal (projector) automotive lamp was the ''Super-Lite'', an auxiliary headlamp produced in a joint venture between
Chrysler Corporation Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
and Sylvania and optionally installed in 1969 and 1970 full-size
Dodge Dodge is an American brand of automobiles and a division of Stellantis, based in Auburn Hills, Michigan. Dodge vehicles have historically included performance cars, and for much of its existence Dodge was Chrysler's mid-priced brand above P ...
automobiles. It used an 85-watt transverse-filament tungsten-halogen bulb and was intended as a mid-beam, to extend the reach of the low beams during turnpike travel when low beams alone were inadequate but high beams would produce excessive glare. Projector main headlamps appeared in 1981 on the Audi Quartz, a concept car designed by Pininfarina for Geneva Auto Salon. Developed more or less simultaneously in Germany by Hella and Bosch and in France by Cibié, the projector low beam permitted accurate beam focus and a much smaller-diameter optical package, though a much deeper one, for any given beam output. The 1986
BMW 7 Series (E32) The BMW E32 is the second generation of the BMW 7 Series luxury cars and was produced from 1986 until 1994. It replaced the E23 and was initially available with straight-six or V12 powerplants. In 1992, V8 engines became available. From its in ...
was the first volume-production car to use polyellipsoidal low beam headlamps. The main disadvantage of this type of headlamp is the need to accommodate the physical depth of the assembly, which may extend far back into the engine compartment.


Light sources


Tungsten

The first electric headlamp light source was the
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
, operating in a
vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or " void". An approximation to such vacuum is a region with a gaseous pressure much less than atmospheric pressure. Physicists often ...
or inert-gas atmosphere inside the headlamp
bulb In botany, a bulb is structurally a short stem with fleshy leaves or leaf basesBell, A.D. 1997. ''Plant form: an illustrated guide to flowering plant morphology''. Oxford University Press, Oxford, U.K. that function as food storage organs dur ...
or sealed beam. Compared to newer-technology light sources, tungsten filaments give off small amounts of light relative to the power they consume. Also, during the normal operation of such lamps, tungsten boils off the surface of the filament and condenses on the bulb glass, blackening it. This reduces the light output of the filament and blocks some of the light that would pass through an unblackened bulb glass, though blackening was less of a problem in sealed beam units; their large interior surface area minimized the thickness of the tungsten accumulation. For these reasons, plain tungsten filaments are all but obsolete in automotive headlamp service.


Tungsten-halogen

Tungsten-halogen technology (also called "quartz-halogen", "quartz-iodine", "iodine cycle", etc.) increases the effective luminous
efficacy Efficacy is the ability to perform a task to a satisfactory or expected degree. The word comes from the same roots as ''effectiveness'', and it has often been used synonymously, although in pharmacology a distinction is now often made between ...
of a
tungsten Tungsten, or wolfram, is a chemical element with the symbol W and atomic number 74. Tungsten is a rare metal found naturally on Earth almost exclusively as compounds with other elements. It was identified as a new element in 1781 and first isol ...
filament: when operating at a higher filament temperature which results in more lumens output per watt input, a tungsten-halogen lamp has a much longer brightness lifetime than similar filaments operating without the halogen regeneration cycle. At equal luminosity, the halogen-cycle bulbs also have longer lifetimes. European-designed halogen headlamp light sources are generally configured to provide more light at the same power consumption as their lower-output plain tungsten counterparts. By contrast, many US-based designs are configured to reduce or minimize the power consumption while keeping light output above the legal minimum requirements; some US tungsten-halogen headlamp light sources produce less initial light than their non-halogen counterparts. A slight theoretical fuel economy benefit and reduced vehicle construction cost through lower wire and switch ratings were the claimed benefits when American industry first chose how to implement tungsten-halogen technology. There was an improvement in seeing distance with US halogen high beams, which were permitted for the first time to produce 150,000
candela The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous t ...
(cd) per vehicle, double the non-halogen limit of 75,000 cd but still well shy of the international European limit of 225,000 cd. After replaceable halogen bulbs were permitted in US headlamps in 1983, the development of US bulbs continued to favor long bulb life and low power consumption, while European designs continued to prioritise optical precision and maximum output. The H1 lamp was the first tungsten-halogen headlamp light source. It was introduced in 1962 by a consortium of European bulb and headlamp makers. This bulb has a single
axial Axial may refer to: * one of the anatomical directions describing relationships in an animal body * In geometry: :* a geometric term of location :* an axis of rotation * In chemistry, referring to an axial bond * a type of modal frame, in music * ...
filament that consumes 55 watts at 12.0
volt The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...
s, and produces 1550 lumens ±15% when operated at 13.2 V. H2 (55 W @ 12.0 V, 1820 lm @ 13.2 V) followed in 1964, and the transverse-filament H3 (55 W @ 12.0 V, 1450 lm ±15%) in 1966. H1 still sees wide use in low beams, high beams and auxiliary
fog Fog is a visible aerosol consisting of tiny water droplets or ice crystals suspended in the air at or near the Earth's surface. Reprint from Fog can be considered a type of low-lying cloud usually resembling stratus, and is heavily influ ...
and
driving lamp Driving is the controlled operation and movement of a vehicle, including cars, motorcycles, trucks, buses, and bicycles. Permission to drive on public highways is granted based on a set of conditions being met and drivers are required to foll ...
s, as does H3. The H2 is no longer a current type, since it requires an intricate bulb holder interface to the lamp, has a short life and is difficult to handle. For those reasons, H2 was withdrawn from ECE Regulation 37 for use in new lamp designs (though H2 bulbs are still manufactured for replacement purposes in existing lamps), but H1 and H3 remain current and these two bulbs were legalised in the United States in 1993. More recent single-filament bulb designs include the H7 (55 W @ 12.0 V, 1500 lm ±10% @ 13.2 V), H8 (35 W @ 12.0 V, 800 lm ±15% @ 13.2 V), H9 (65 W @ 12.0 V, 2100 lm ±10% @ 13.2 V), and H11 (55 W @ 12.0 V, 1350 lm ±10% @ 13.2 V). 24-volt versions of many bulb types are available for use in trucks, buses, and other commercial and military vehicles. The first dual-filament halogen bulb to produce both a low and a high beam, the H4 (60/55 W @ 12 V, 1650/1000 lm ±15% @ 13.2 V), was released in 1971 and quickly became the predominant headlamp bulb throughout the world except in the United States, where the H4 is still not legal for automotive use. In 1989, the Americans created their own standard for a bulb called HB2: almost identical to H4 except with more stringent constraints on filament geometry and positional variance, and power consumption and light output expressed at the US test voltage of 12.8V. The first US halogen headlamp bulb, introduced in 1983, was the HB1/9004. It is a 12.8-volt, transverse dual-filament design that produces 700 lumens on low beam and 1200 lumens on high beam. The 9004 is rated for 65 watts (high beam) and 45 watts (low beam) at 12.8 volts. Other US approved
halogen The halogens () are a group in the periodic table consisting of five or six chemically related elements: fluorine (F), chlorine (Cl), bromine (Br), iodine (I), astatine (At), and tennessine (Ts). In the modern IUPAC nomenclature, this grou ...
bulbs include the HB3 (65 W, 12.8 V), HB4 (55 W, 12.8 V), and HB5 (65/55 watts, 12.8 V).NHTSA Docket 3397: Replaceable Light Source Information for headlight bulbs
/ref> All of the European-designed and internationally approved bulbs except H4 are presently approved for use in headlamps complying with US requirements.


Halogen infrared reflective (HIR)

A further development of the tungsten-halogen bulb has a dichroic coating that passes
visible light Light or visible light is electromagnetic radiation that can be perceived by the human eye. Visible light is usually defined as having wavelengths in the range of 400–700 nanometres (nm), corresponding to frequencies of 750–420 t ...
and reflects infrared radiation. The glass in such a bulb may be
spherical A sphere () is a geometrical object that is a three-dimensional analogue to a two-dimensional circle. A sphere is the set of points that are all at the same distance from a given point in three-dimensional space.. That given point is the ce ...
or tubular. The reflected infrared radiation strikes the filament located at the center of the glass envelope, heating the filament to a greater degree than can be achieved through
resistive heating Joule heating, also known as resistive, resistance, or Ohmic heating, is the process by which the passage of an electric current through a conductor produces heat. Joule's first law (also just Joule's law), also known in countries of former ...
alone. The superheated filament emits more light without an increase in power consumption.


High-intensity discharge (HID)

High-intensity discharge lamp High-intensity discharge lamps (HID lamps) are a type of electrical gas-discharge lamp which produces light by means of an electric arc between tungsten electrodes housed inside a translucent or transparent fused quartz or fused alumina arc tu ...
s (HID) produce light with an
electric arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. ...
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. Automotive HID may be generically called "xenon headlamps", though they are actually metal-halide lamps that contain
xenon Xenon is a chemical element with the symbol Xe and atomic number 54. It is a dense, colorless, odorless noble gas found in Earth's atmosphere in trace amounts. Although generally unreactive, it can undergo a few chemical reactions such as the ...
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 Argon is a chemical element with the symbol Ar and atomic number 18. It is in group 18 of the periodic table and is a noble gas. Argon is the third-most abundant gas in Earth's atmosphere, at 0.934% (9340 ppmv). It is more than twice a ...
, 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. In the United States, vehicle lighting that does not conform to FMVSS 108 is not street legal. 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. In the US, suppliers, importers and vendors that offer non-compliant kits are subject to civil fines. By October 2004, the
NHTSA The National Highway Traffic Safety Administration (NHTSA ) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" rel ...
had investigated 24 suppliers and all resulted in termination of sale or recalls. In Europe and the many non-European countries applying ECE Regulations, even HID headlamps designed as such must be equipped with lens cleaning and automatic self-leveling systems, except on motorcycles. 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 ''Hella'' is an American slang term that originated in the San Francisco Bay Area. It is used as an intensifying adverb such as in "hella bad" or "hella good" and was eventually added to the '' Oxford English Dictionary'' in 2002. It is possib ...
and Bosch beginning in 1992 for optional availability on the
BMW 7 Series The BMW 7 Series is a full-size luxury sedan manufactured and marketed by the German automaker BMW since 1977. It is the successor to the BMW E3 "New Six" sedan and is now in its seventh generation. The 7 Series is BMW's flagship car and is ...
. This first system uses a built-in, non-replaceable bulb without a UV-blocking glass shield or touch-sensitive electrical safety cutout, designated D1 – 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 Sylvania and designated ''Type 9500''. This was the only system to operate on DC, since reliability proved inferior to the AC systems. The Type 9500 system was not used on any other models, and was discontinued after
Osram Osram Licht AG is a German company that makes electric lights, headquartered in Munich and Premstätten (Austria). Osram positions itself as a high-tech photonics company that is increasingly focusing on sensor technology, visualization and t ...
's takeover of Sylvania in 1997. 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) The second generation of the Mercedes-Benz CL-Class is the C215-chassis coupé of 1998–2006. It is based on the 1998–2005 Mercedes-Benz S-Class (W220), though it rides on an shorter wheelbase. Sales in Germany started in August 1999 for the ...
.


Operation

HID headlamp bulbs do not run on low-voltage DC current, so they require a
ballast Ballast is material that is used to provide stability to a vehicle or structure. Ballast, other than cargo, may be placed in a vehicle, often a ship or the gondola of a balloon or airship, to provide stability. A compartment within a boat, ship ...
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 High voltage electricity refers to electrical potential large enough to cause injury or damage. In certain industries, ''high voltage'' refers to voltage above a certain threshold. Equipment and conductors that carry high voltage warrant sp ...
pulse is used to produce an
electrical arc An electric arc, or arc discharge, is an electrical breakdown of a gas that produces a prolonged electrical discharge. The current through a normally nonconductive medium such as air produces a plasma; the plasma may produce visible light. A ...
– in a manner similar to a
spark plug A spark plug (sometimes, in British English, a sparking plug, and, colloquially, a plug) is a device for delivering electric current from an ignition system to the combustion chamber of a spark-ignition engine to ignite the compressed fuel/ai ...
– 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 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 The volt (symbol: V) is the unit of electric potential, electric potential difference (voltage), and electromotive force in the International System of Units (SI). It is named after the Italian physicist Alessandro Volta (1745–1827). Defin ...
s 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 The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose expression in terms of SI base units is s−1, meaning that o ...
or higher. The command is often near the steering wheel and a specific indicator is shown on the dashboard.


Bulb types

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 V.  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 Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30  PHz) to 400 nm (750  THz), shorter than that of visible light, but longer than X-rays. UV radiation ...
(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 Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
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.


Color

The
correlated color temperature Color temperature is the color of light emitted by an idealized opaque, non-reflective body at a particular temperature measured in kelvins. The color temperature scale is used to categorize the color of light emitted by other light sources ...
of factory installed automotive HID headlamps is between 4200K while tungsten-halogen lamps are at 3000K to 3550K. The
spectral power distribution In radiometry, photometry, and color science, a spectral power distribution (SPD) measurement describes the power per unit area per unit wavelength of an illumination ( radiant exitance). More generally, the term ''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 A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with a natural or standard light source. Light sources with a high CRI are desirable in ...
(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.


Advantages


= Increased safety

= Automotive HID lamps offer about 3000 lumens and 90 Mcd/m2 versus 1400 lumens and 30 Mcd/m2 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. Hence, good HID headlamps contribute to driving safety. 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. 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.


Disadvantages


= Glare

= Vehicles equipped with HID headlamps (except motorcycles) are required by ECE regulation 48 also to be equipped with headlamp lens cleaning systems 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 Glare (derived from GLAss REinforced laminate ) is a fiber metal laminate (FML) composed of several very thin layers of metal (usually aluminum) interspersed with layers of S-2 glass-fiber ''pre-preg'', bonded together with a matrix such as epo ...
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; HID headlamps are markedly less prevalent in the US, where they have produced significant glare complaints.NHTSA headlamp glare docket
/ref> 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.


= Mercury content

= HID headlamp bulb types D1R, D1S, D2R, D2S and 9500 contain the toxic heavy metal mercury. The disposal of mercury-containing vehicle parts is increasingly regulated throughout the world, for example unde
US EPA regulations
Newer HID bulb designs D3R, D3S, D4R, and D4S which are in production since 2004 contain no mercury, 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.


LED


Timeline

Automotive headlamp applications using
light-emitting diode A light-emitting diode (LED) is a semiconductor Electronics, device that Light#Light sources, emits light when Electric current, current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy i ...
s (LEDs) have been undergoing development since 2004. In 2006 the first series-production LED low beams were factory-installed on the Lexus LS 600h / LS 600h L. The high beam and turn signal functions used filament bulbs. The headlamp was supplied by Koito Industries Ltd. In 2007 the first headlamps with all functions provided by LEDs, supplied by
AL-Automotive Lighting Automotive Lighting (AL) is an automotive lighting company that is based in Germany. It was founded in 1999 as a 50-50 joint venture between the Italian firm Magneti Marelli and the German firm Robert Bosch GmbH (K2 Lighting division). In 2001, M ...
, were introduced on the V10 Audi R8 sports car (except in North America). In 2009
Hella ''Hella'' is an American slang term that originated in the San Francisco Bay Area. It is used as an intensifying adverb such as in "hella bad" or "hella good" and was eventually added to the '' Oxford English Dictionary'' in 2002. It is possib ...
headlamps on the 2009 Cadillac Escalade Platinum became the first all-LED headlamps for the North American market. In 2010 the first all-LED headlamps with adaptive high beam and what Mercedes called the "Intelligent Light System" were introduced on the 2011 Mercedes CLS. In 2013 the first digitally controlled full-LED glare-free "Matrix LED" adaptive headlamps were introduced by
Audi Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide. ...
on the facelifted A8, with 25 individual LED segments. The system dims the light that would shine directly onto oncoming and preceding vehicles, but continues to cast its full light on the zones between and beside them. This works because the LED high beams are split into numerous individual light-emitting diodes. High-beam LEDs in both headlights are arranged in a matrix and adapt fully electronically to the surroundings in milliseconds. They are activated and deactivated or dimmed individually by a control unit. In addition, the headlights also function as a cornering light. Using predictive route data supplied by the MMI navigation plus, the focus of the beam is shifted towards the bend even before the driver turns the steering wheel. In 2014:
Mercedes-Benz Mercedes-Benz (), commonly referred to as Mercedes and sometimes as Benz, is a German luxury and commercial vehicle automotive brand established in 1926. Mercedes-Benz AG (a Mercedes-Benz Group subsidiary established in 2019) is headquarte ...
introduced a similar technology on the facelifted CLS-Class in 2014, called Multibeam LED, with 24 individual segments. As of 2010, LED headlamps such as those available on the
Toyota Prius The is a car built by Toyota which has a hybrid drivetrain, combining an internal combustion engine with an electric motor. Initially offered as a four-door sedan, it has been produced only as a five-door liftback since 2003. In 2007, ...
were providing output between halogen and HID headlamps, with system power consumption slightly lower than other headlamps, longer lifespans, and more flexible design possibilities. As LED technology continues to evolve, the performance of LED headlamps was predicted to improve to approach, meet, and perhaps one day surpass that of HID headlamps. That occurred by mid-2013, when the Mercedes S-Class came with LED headlamps giving higher performance than comparable HID setups.


Cold lenses

Before LEDs, all light sources used in headlamps (tungsten, halogen, HID) emitted
infrared Infrared (IR), sometimes called infrared light, is electromagnetic radiation (EMR) with wavelengths longer than those of Light, visible light. It is therefore invisible to the human eye. IR is generally understood to encompass wavelengths from ...
energy that can thaw built-up snow and ice off a headlamp lens and prevent further accumulation. LEDs do not. Some LED headlamps move heat from the heat sink on the back of the LEDs to the inner face of the front lens to warm it up, while on others no provision is made for lens thawing.


Laser

A laser lamp uses mirrors to direct a
laser A laser is a device that emits light through a process of optical amplification based on the stimulated emission of electromagnetic radiation. The word "laser" is an acronym for "light amplification by stimulated emission of radiation". The ...
on to a
phosphor A phosphor is a substance that exhibits the phenomenon of luminescence; it emits light when exposed to some type of radiant energy. The term is used both for fluorescent or phosphorescent substances which glow on exposure to ultraviolet or v ...
that then emits a light. Laser lamps use half as much power as
LED lamp An LED lamp or LED light bulb is an electric light that produces light using light-emitting diodes (LEDs). LED lamps are significantly more energy-efficient than equivalent incandescent lamps and can be significantly more efficient than mo ...
s. They were first developed by
Audi Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide. ...
for use as headlamps in the
24 Hours of Le Mans The 24 Hours of Le Mans (french: link=no, 24 Heures du Mans) is an endurance-focused sports car race held annually near the town of Le Mans, France. It is the world's oldest active endurance racing event. Unlike fixed-distance races whose ...
. In 2014, the BMW i8 became the first production car to be sold with an auxiliary high-beam lamp based on this technology. The limited-production Audi R8 LMX uses lasers for its spot lamp feature, providing illumination for high-speed driving in low-light conditions. The
Rolls-Royce Phantom VIII The Rolls-Royce Phantom is a full-sized luxury saloon manufactured by Rolls-Royce Motor Cars. It is the eighth and current generation of the Rolls-Royce Phantom, debuting in 2017, and the second launched by Rolls-Royce under BMW ownership. It ...
employs laser headlights with a high beam range of over 600 meters.


Automatic headlamps

Automatic systems for activating the headlamps have been available since the mid-1950s, originally only on luxury American models such as Cadillac's
Twilight Sentinel Twilight Sentinel is a device on General Motors cars that senses outside light and turns the exterior lights on and off depending on lighting conditions. In addition, Twilight Sentinel also allows the driver to set a timer (located with the headl ...
, Lincoln, and Imperial. Basic implementations turn the headlights on at dusk and off at dawn. Modern implementations use sensors to detect the amount of exterior light. UN R48 has mandated the installation of automatic headlamps since 30 July 2016. With a daytime running lamp equipped and operated, the dipped beam headlamp should automatically turn on if the car is driving in less than 1,000 lux ambient conditions such as in a tunnel and in dark environments. While in such situations, a daytime running lamp would make glare more evident to the upcoming vehicle driver, which in turn would influence the upcoming vehicle driver's eyesight, such that, by automatically switching the daytime running lamp to the dipped-beam headlamp, the inherent safety defect could be solved and safety benefit ensured.


Beam aim control


Headlamp leveling systems

The 1948 Citroën 2CV was launched in France with a manual headlamp leveling system, controlled by the driver with a knob through a mechanical rod linkage. This allowed the driver to adjust the vertical aim of the headlamps to compensate for the passenger and cargo load in the vehicle. In 1954,
Cibié Valeo is a French global automotive supplier headquartered in France, listed on the Paris Stock Exchange ( CAC-40 Index). It supplies a wide range of products to automakers and the aftermarket. The Group employs 113,600 people in 33 countries w ...
introduced an automatic headlamp leveling system linked to the vehicle's suspension system to keep the headlamps correctly aimed regardless of vehicle load, without driver intervention. The first vehicle to be so equipped was the
Panhard Dyna Z The Panhard Dyna Z is a lightweight motor car produced by Panhard of France from 1954 to 1959. It was first presented to the press at a Paris restaurant named Les Ambassadeurs on 17 June 1953 and entered production the following year. In 1959, i ...
. Beginning in the 1970s, Germany and some other European countries began requiring remote-control headlamp leveling systems that permit the driver to lower the lamps' aim by means of a dashboard control lever or knob if the rear of the vehicle is weighted down with passengers or cargo, which would tend to raise the lamps' aim angle and create glare. Such systems typically use
stepper motor A stepper motor, also known as step motor or stepping motor, is a brushless DC electric motor that divides a full rotation into a number of equal steps. The motor's position can be commanded to move and hold at one of these steps without any posi ...
s at the headlamp and a rotary switch on the dash marked "0", "1", "2", "3" for different beam heights, "0" being the "normal" (and highest) position for when the car is lightly loaded. Internationalized
ECE Regulation The World Forum for Harmonization of Vehicle Regulations is a working party (WP.29) of the Inland Transport Committee (ITC) of the United Nations Economic Commission for Europe (UNECE). Its responsibility is to manage the multilateral Agreements ...
48, in force in most of the world outside North America, currently specifies a limited range within which the vertical aim of the headlamps must be maintained under various vehicle load conditions; if the vehicle isn't equipped with an adaptive suspension sufficient to keep the headlamps aimed correctly regardless of load, a headlamp leveling system is required.  The regulation stipulates a more stringent version of this anti-glare measure if the vehicle has headlamps with low beam light source(s) that produce more than 2,000 lumens – xenon bulbs and certain high-power halogens, for example. Such vehicles must be equipped with headlamp self-leveling systems that sense the vehicle's degree of squat due to cargo load and road inclination, and automatically adjust the headlamps' vertical aim to keep the beam correctly oriented without any action required by the driver. Leveling systems are not required by the North American regulations. A 2007 study, however, suggests automatic levelers on all headlamps, not just those with high-power light sources, would give drivers substantial safety benefits of better seeing and less glare.


Directional headlamps

These provide improved lighting for cornering. Some automobiles have their headlamps connected to the
steering Steering is a system of components, linkages, and other parts that allows a driver to control the direction of the vehicle. Introduction The most conventional steering arrangement allows a driver to turn the front wheels of a vehicle using ...
mechanism so the lights will follow the movement of the front wheels. Czechoslovak Tatra was an early implementer of such a technique, producing in the 1930s a vehicle with a central directional headlamp. The American 1948 Tucker Sedan was likewise equipped with a third central headlamp connected mechanically to the steering system. The 1967 French Citroën DS and 1970 Citroën SM were equipped with an elaborate dynamic headlamp positioning system that adjusted the inboard headlamps' horizontal and vertical position in response to inputs from the vehicle's steering and suspension systems. At that time US regulations required this system to be removed from those models sold in the U.S. The D series cars equipped with the system used cables connecting the long-range headlamps to a lever on the steering relay while the inner long-range headlamps on the SM used a sealed hydraulic system using a glycerin-based fluid instead of mechanical cables. Both these systems were of the same design as their respective cars' headlamp leveling systems. The cables of the D system tended to rust in the cable sheaths while the SM system gradually leaked fluid, causing the long-range lamps to turn inward, looking "cross-eyed." A manual adjustment was provided but once it was to the end of its travel the system required refilling with fluid or replacement of the tubes and dashpots. Citroën SM non-US market vehicles were equipped with heating of the headlamp cover glasses, this heat supplied by ducts carrying warm air from the radiator exhaust to the space between the headlamp lenses and the cover glasses. This provided demisting/defogging of the entire interior of the cover glasses, keeping the glass clear of mist/fog over the entire surface. The glasses have thin stripes on their surfaces that are heated by the headlight beams; however, the ducted warm air provides demisting when the headlamps are not turned on. The glasses' stripes on both D and SM cars appear similar to rear windshield glass electric defogger heating strips, but they are passive, not electrified.


Advanced front-lighting system (AFS)

Beginning in the 2000s, there was a resurgence in interest in the idea of moving or optimizing the headlight beam in response not only to vehicular steering and suspension dynamics, but also to ambient weather and visibility conditions, vehicle speed, and road curvature and contour. A task force under the EUREKA organization, composed primarily of European automakers, lighting companies and regulators began working to develop design and performance specifications for what is known as Adaptive Front-Lighting Systems, commonly ''AFS''. Manufacturers such as BMW,
Toyota is a Japanese multinational automotive manufacturer headquartered in Toyota City, Aichi, Japan. It was founded by Kiichiro Toyoda and incorporated on . Toyota is one of the largest automobile manufacturers in the world, producing about 10 ...
, Škoda, and
Vauxhall Vauxhall ( ) is a district in South West London, part of the London Borough of Lambeth, England. Vauxhall was part of Surrey until 1889 when the County of London was created. Named after a medieval manor, "Fox Hall", it became well known for ...
/
Opel Opel Automobile GmbH (), usually shortened to Opel, is a German automobile manufacturer which has been a subsidiary of Stellantis since 16 January 2021. It was owned by the American automaker General Motors from 1929 until 2017 and the PSA Grou ...
have released vehicles equipped with AFS since 2003. Rather than the mechanical linkages employed in earlier directional-headlamp systems, AFS relies on electronic sensors,
transducer A transducer is a device that converts energy from one form to another. Usually a transducer converts a signal in one form of energy to a signal in another. Transducers are often employed at the boundaries of automation, measurement, and con ...
s, and actuators. Other AFS techniques include special auxiliary optical systems within a vehicle's headlamp housings. These auxiliary systems may be switched on and off as the vehicle and operating conditions call for light or darkness at the angles covered by the beam the auxiliary optics produce. A typical system measures steering angle and vehicle speed to swivel the headlamps. The most advanced AFS systems use GPS signals to anticipate changes in road curvature, rather than simply reacting to them.


Automatic beam switching

Even when conditions would warrant the use of high-beam headlamps, drivers often do not use them. There have long been efforts, particularly in America, to devise an effective automatic beam selection system to relieve the driver of the need to select and activate the correct beam as traffic, weather, and road conditions change.
General Motors The General Motors Company (GM) is an American Multinational corporation, multinational Automotive industry, automotive manufacturing company headquartered in Detroit, Michigan, United States. It is the largest automaker in the United States and ...
introduced the first automatic headlight dimmer called the 'Autronic Eye' in 1952 on their
Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed ...
,
Buick Buick () is a division of the American automobile manufacturer General Motors (GM). Started by automotive pioneer David Dunbar Buick in 1899, it was among the first American marques of automobiles, and was the company that established General ...
, and
Oldsmobile Oldsmobile or formally the Oldsmobile Division of General Motors was a brand of American automobiles, produced for most of its existence by General Motors. Originally established as "Olds Motor Vehicle Company" by Ransom E. Olds in 1897, it pro ...
models; the feature was offered in other GM vehicles starting in 1953. The system's phototube and associated circuitry were housed in a gunsight-like tube atop the dashboard. An amplifier module was located in the engine compartment that controlled the headlight relay using signals from the dashboard-mounted tube unit. This pioneering setup gave way in 1958 to a system called 'GuideMatic' in reference to GM's ''Guide'' lighting division. The GuideMatic had a more compact dashtop housing and a control knob that allowed the driver to adjust the system's sensitivity threshold to determine when the headlamps would be dipped from high to low beam in response to an oncoming vehicle. By the early 1970s, this option was withdrawn from all GM models except
Cadillac The Cadillac Motor Car Division () is a division of the American automobile manufacturer General Motors (GM) that designs and builds luxury vehicles. Its major markets are the United States, Canada, and China. Cadillac models are distributed ...
, on which GuideMatic was available through 1988. The photosensor for this system used an amber lens, and the adoption of retro-reflective yellow road signs, such as for oncoming curves, caused them to dim prematurely - possibly leading to their discontinuation. Ford- and
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
-built vehicles were also available with the GM-made dimmers from the 1950s through the 1980s. A system called 'AutoDim' was offered on several Lincoln models starting in the mid-1950s, and eventually the
Ford Thunderbird The Ford Thunderbird (colloquially called the T-Bird) is a personal luxury car produced by Ford from model years 1955 until 1997 and 2002 until 2005 across 11 distinct generations. Introduced as a two-seat convertible, the Thunderbird was pr ...
and some Mercury models offered it as well. Premium
Chrysler Stellantis North America (officially FCA US and formerly Chrysler ()) is one of the " Big Three" automobile manufacturers in the United States, headquartered in Auburn Hills, Michigan. It is the American subsidiary of the multinational automotiv ...
and
Imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas ...
models offered a system called ''Automatic Beam Control'' throughout the 1960s and early 1970s.


Rabinow dimmer

Though the systems based on photoresistors evolved, growing more compact and moving from the dashboard to a less conspicuous location behind the radiator grill, they were still unable to reliably discern headlamps from non-vehicular light sources such as streetlights. They also did not dip to low beam when the driver approached a vehicle from behind, and they would spuriously dip to low beam in response to road sign reflections of the vehicle's own high beam headlamps. American inventor Jacob Rabinow devised and refined a scanning automatic dimmer system impervious to streetlights and reflections, but no automaker purchased the rights, and the problematic photoresistor type remained on the market through the late 1980s.


Bone-Midland lamps

In 1956, the inventor Even P. Bone developed a system where a vane in front of each headlight moved automatically and caused a shadow in front of the approaching vehicle, allowing for high beam use without glare for the approaching driver. The system, called "Bone-Midland Lamps," was never taken up by any car manufacturer.


Camera-based dimmer

Present systems based on imaging
CMOS Complementary metal–oxide–semiconductor (CMOS, pronounced "sea-moss", ) is a type of metal–oxide–semiconductor field-effect transistor (MOSFET) fabrication process that uses complementary and symmetrical pairs of p-type and n-type MOSF ...
cameras can detect and respond appropriately to leading and oncoming vehicles while disregarding streetlights, road signs, and other spurious signals. Camera-based beam selection was first released in 2005 on the
Jeep Grand Cherokee The Jeep Grand Cherokee is a range of mid-size SUVs produced by the American manufacturer Jeep. At its introduction, while most SUVs were still manufactured with body-on-frame construction, the Grand Cherokee has used a unibody chassis from the ...
and has since then been incorporated into comprehensive
driver assistance An advanced driver-assistance system (ADAS) is any of a groups of electronic technologies that assist drivers in driving and parking functions. Through a safe human-machine interface, ADAS increase car and road safety. ADAS uses automated technol ...
systems by automakers worldwide. The headlights will dim when a bright reflection bounces off of a street sign.


Intelligent Light System

''Intelligent Light System'' is a headlamp beam control system introduced in 2006 on the
Mercedes-Benz E-Class (W211) The Mercedes-Benz W211 is the third generation Mercedes-Benz E-Class made from 2002 to 2009 in sedan/saloon and station wagon/estate configurations – replacing the W210 E-Class models and superseded by the Mercedes-Benz W212 in 2009. The C219 ...
which offers five different bi-xenon light functions, each of which is suited to typical driving or weather conditions: * Country mode * Motorway mode * Enhanced fog lamps * Active light function ( Advanced front-lighting system (AFS)) * Cornering light function


Adaptive highbeam

''Adaptive Highbeam Assist'' is
Mercedes-Benz Mercedes-Benz (), commonly referred to as Mercedes and sometimes as Benz, is a German luxury and commercial vehicle automotive brand established in 1926. Mercedes-Benz AG (a Mercedes-Benz Group subsidiary established in 2019) is headquarte ...
' marketing name for a headlight control strategy that continuously automatically tailors the headlamp range so the beam just reaches other vehicles ahead, thus always ensuring maximum possible seeing range without glaring other road users. It was first launched in the Mercedes E-class in 2009. It provides a continuous range of beam reach from a low-aimed low beam to a high-aimed high beam, rather than the traditional binary choice between low and high beams. The range of the beam can vary between 65 and 300 meters, depending on traffic conditions. In traffic, the low beam cutoff position is adjusted vertically to maximise seeing range while keeping glare out of leading and oncoming drivers' eyes. When no traffic is close enough for glare to be a problem, the system provides full high beam. Headlamps are adjusted every 40 milliseconds by a camera on the inside of the front windscreen which can determine distance to other vehicles. The S-Class, CLS-Class and C-Class also offer this technology. In the CLS, the adaptive high beam is realised with LED headlamps - the first vehicle producing all adaptive light functions with LEDs. Since 2010 some
Audi Audi AG () is a German automotive manufacturer of luxury vehicles headquartered in Ingolstadt, Bavaria, Germany. As a subsidiary of its parent company, the Volkswagen Group, Audi produces vehicles in nine production facilities worldwide. ...
models with Xenon headlamps are offering a similar system: adaptive light with
variable headlight range control A headlamp is a lamp attached to the front of a vehicle to illuminate the road ahead. Headlamps are also often called headlights, but in the most precise usage, ''headlamp'' is the term for the device itself and ''headlight'' is the term fo ...
. In Japan, the
Toyota Crown The is an automobile which has been produced by Toyota in Japan since 1955. It is primarily a line of mid-size luxury cars that is marketed as an upmarket offering in the Toyota lineup. Introduced in 1955 as the Toyopet Crown, it has served ...
, Toyota Crown Majesta,
Nissan Fuga The Nissan Fuga (Japanese: 日産・フーガ ''Nissan Fūga'') is a mid-size luxury sedan produced by Japanese automaker Nissan since October 2004. It is built on a wider, stretched wheelbase version of the Nissan FM platform. After the Nissan ...
and Nissan Cima offer the technology on top level models. Until Feb 2022, this technology had been illegal in the US, as FMVSS 108 specifically stated that headlamps must have dedicated high and low beams to be deemed road-legal. An infrastructure bill enacted in November 2021 included language that directs the
National Highway Traffic Safety Administration The National Highway Traffic Safety Administration (NHTSA ) is an agency of the U.S. federal government, part of the Department of Transportation. It describes its mission as "Save lives, prevent injuries, reduce vehicle-related crashes" relat ...
to amend FMVSS 108 to allow the use of this technology, and set a two-year deadline for implementing this change. In Feb 2022, the NHTSA amended FMVSS 108 allowing adaptive headlights for use in the US.


Glare-free high beam and pixel light

A ''glare-free high beam'' is a camera-driven dynamic lighting control strategy that selectively shades spots and slices out of the high beam pattern to protect other road users from glare, while continuously providing the driver with maximum seeing range. The area surrounding other road users is constantly illuminated at high beam intensity, but without the glare that would typically result from using uncontrolled high beams in traffic. This constantly changing beam pattern requires complex sensors, microprocessors, and actuators because the vehicles which must be shadowed out of the beam are constantly moving. The dynamic shadowing can be achieved with movable shadow masks shifted within the light path inside the headlamp. Or, the effect can be achieved by selectively darkening addressable LED emitters or reflector elements, a technique known as ''pixel light''. The first mechanically controlled (non-LED), glare-free high beam was Volkswagen's "Dynamic Light Assist" package, which was introduced in 2010 on the
Volkswagen Touareg The Volkswagen Touareg (German pronunciation: ) is a car produced by German automaker Volkswagen Group since 2002 at the Volkswagen Bratislava Plant. A five-seater mid-size luxury crossover SUV, the vehicle was named after the nomadic Tuareg peo ...
, Phaeton, and Passat. In 2012, the facelifted
Lexus LS (XF40) The Lexus LS (XF40) is the fourth generation of the Lexus LS line of full-size luxury sedans. Lexus debuted the model line at the 2006 North American International Auto Show, with variants including the standard wheelbase LS 460 (USF40) and ...
introduced an identical bi-xenon system: "Adaptive High-beam System". The first mechanically controlled LED glare-free headlamps were introduced in 2012 on
BMW 7 Series The BMW 7 Series is a full-size luxury sedan manufactured and marketed by the German automaker BMW since 1977. It is the successor to the BMW E3 "New Six" sedan and is now in its seventh generation. The 7 Series is BMW's flagship car and is ...
: "Selective Beam" (anti-dazzle high-beam assistant). In 2013
Mercedes-Benz Mercedes-Benz (), commonly referred to as Mercedes and sometimes as Benz, is a German luxury and commercial vehicle automotive brand established in 1926. Mercedes-Benz AG (a Mercedes-Benz Group subsidiary established in 2019) is headquarte ...
introduced the same LED system: "Adaptive Highbeam Assist Plus". The first digitally controlled LED glare-free headlamps were introduced in 2013 on Audi A8. See LED section.


Care

Headlamp systems require periodic maintenance. Sealed beam headlamps are modular; when the
filament The word filament, which is descended from Latin ''filum'' meaning " thread", is used in English for a variety of thread-like structures, including: Astronomy * Galaxy filament, the largest known cosmic structures in the universe * Solar filament ...
burns out, the entire sealed beam is replaced. Most vehicles in North America made since the late 1980s use headlamp lens-reflector assemblies that are considered a part of the car, and just the bulb is replaced when it fails. Manufacturers vary the means by which the bulb is accessed and replaced. Headlamp aim must be properly checked and adjusted frequently, for misaimed lamps are dangerous and ineffective. Over time, the headlamp lens can deteriorate. It can become pitted due to abrasion of road sand and pebbles and can crack, admitting water into the headlamp. "Plastic" (
polycarbonate Polycarbonates (PC) are a group of thermoplastic polymers containing carbonate groups in their chemical structures. Polycarbonates used in engineering are strong, tough materials, and some grades are optically transparent. They are easily work ...
) lenses can become cloudy and discoloured. This is due to oxidation of the painted-on lens hardcoat by ultraviolet light from the sun and the headlamp bulbs. If it is minor, it can be polished out using a reputable brand of a car polish that is intended for restoring the shine to chalked paint. In more advanced stages, the deterioration extends through the actual plastic material, rendering the headlamp useless and necessitating complete replacement. Sanding or aggressively polishing the lenses, or plastic headlight restoration, can buy some time, but doing so removes the protective coating from the lens, which when so stripped will deteriorate faster and more severely. Kits for a quality repair are available that allow the lens to be polished with progressively finer abrasives, and then be sprayed with an aerosol of ultra violet resistant clear coating. The reflector, made out of vaporized aluminum deposited in an extremely thin layer on a metal, glass, or plastic substrate, can become dirty, oxidised, or burnt, and lose its specularity. This can happen if water enters the headlamp, if bulbs of higher than specified wattage are installed, or simply with age and use. Reflectors thus degraded, if they cannot be cleaned, must be replaced.


Lens cleaners

Dirt buildup on headlamp lenses increases glare to other road users, even at levels too low to reduce seeing performance significantly for the driver. Therefore, headlamp lens cleaners are required by UN Regulation 48 on vehicles equipped with low-beam headlamps using light sources that have a reference luminous flux of 2,000 lumens or more. This includes all HID headlamps and some high-power halogen units. Some cars have lens cleaners fitted even where the regulations do not require them. North America, for example, does not use UN regulations, and FMVSS 108 does not require lens cleaners on any headlamps, though they are permitted. Lens cleaning systems come in two main varieties: a small motor-driven rubber wiper or brush conceptually similar to windshield wipers, or a fixed or telescopic high-pressure sprayer which cleans the lenses with a spray of windshield washer fluid. Most recent lens cleaning systems are of the spray type because UN regulations do not permit mechanical cleaning systems (wipers) to be used with plastic-lens headlamps, and most recent headlamps have plastic lenses. Some cars with retractable headlamps, such as the original Mazda MX-5, have a squeegee at the front of the lamp recess which automatically wipes the lenses as they are raised or lowered, although it does not provide washer fluid.


See also

* Automotive lamp types *
Automotive lighting The lighting system of a motor vehicle consists of lighting and signalling devices mounted to or integrated into the front, rear, sides, and in some cases the top of a motor vehicle. They illuminate the road ahead for the driver and increase th ...
*
Automotive night vision An automotive night vision system uses a thermographic camera to increase a driver's perception and seeing distance in darkness or poor weather beyond the reach of the vehicle's headlights. Such systems are offered as optional equipment on cert ...
* Headlamp tester * Headlamp (outdoor) *
Headlight flashing Headlight flashing is the act of either briefly switching on the headlights of a car, or of momentarily switching between a headlight's high beams and low beams, in an effort to communicate with another driver or drivers. The signal is sometimes ...
* ISIRI 6672 * Lighting-up time * Train lights *
Twilight Sentinel Twilight Sentinel is a device on General Motors cars that senses outside light and turns the exterior lights on and off depending on lighting conditions. In addition, Twilight Sentinel also allows the driver to set a timer (located with the headl ...
*
World Forum for Harmonization of Vehicle Regulations The World Forum for Harmonization of Vehicle Regulations is a working party (WP.29) of the Inland Transport Committee (ITC) of the United Nations Economic Commission for Europe (UNECE). Its responsibility is to manage the multilateral Agreements ...


References


External links

* {{CarDesign nav Articles containing video clips Automotive lamps