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 for the beam of light produced and distributed by the device. 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 or a small generator mechanically integrated into the workings of the bicycles. The first horseless carriages used carriage lamps, which proved unsuitable for travel at speed. The earliest headlamps, fueled by acetylene or oil, operated from the late s. Acetylene lamps were popular because the flame is resistant to wind and rain.
The first electric headlamps were introduced in on the Columbia Electric Car from the Electric Vehicle Company of Hartford, Connecticut , 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.
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A number of manufacturers offered "Prest-O-Lite" acetylene lights as standard equipment for , and Peerless made electric headlamps standard in A Birmingham [ where? In Cadillac 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 , but the 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 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 by Guide Lamp called the "Duplo". In the foot-operated dimmer switch or dip switch was introduced and became standard for much of the century. From highest to lowest, the beams were called "country passing", "country driving" and "city driving". The 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.
Directional lighting, using a switch and electromagnetically shifted reflector to illuminate the curbside only, was introduced in the rare, one-year-only Tatra. Steering-linked lighting was featured on the Tucker Torpedo's center-mounted headlight, and was later popularized by the Citroen DS. This made it possible to turn the light in the direction of travel when the steering wheel turned, and is now widely adopted technology.
Britain, Australia, and some other Commonwealth countries, as well as Japan and Sweden , also made extensive use of 7-inch sealed beams, though they were not mandated as they were in the United States. This led to different front-end designs for each side of the Atlantic for decades. Technology moved forward in the rest of the world. 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. Beyond the engineering, performance and regulatory-compliance aspects of headlamps, there is the consideration of the various ways they are designed and arranged on a motor vehicle.
Headlamps were round for many years, because that is the native shape of a parabolic reflector. Using principles of reflection, the simple symmetric round reflective surface projects light and helps focus the beam.
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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. They were prohibited in the United States where round lamps were required until Headlight design in the U. However, the Tucker 48 included a defining "cyclops-eye" feature: a third center-mounted headlight connected to the car's steering mechanism.
Separate low and high beam lamps eliminated the need for compromise in lens design and filament positioning required in a single unit. The four-lamp system permitted more design flexibility and improved low and high beam performance. An example arrangement includes the stacking of two headlamps on each side, with low beams above high beams. The Nash Ambassador used this arrangement in the model year. Also in the model year, the Buick Riviera had concealable stacked headlamps.
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Various Mercedes models sold in America used this arrangement because their home-market replaceable-bulb headlamps were illegal in the US. In the late s and early s, some Lincoln , Buick , and Chrysler cars had the headlamps arranged diagonally with the low-beam lamps outboard and above the high-beam lamps. In , the newly-initiated Federal Motor Vehicle Safety Standard 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.
This made it difficult for vehicles with headlamp configurations designed for good aerodynamic performance to achieve it in their US-market configurations. When FMVSS was amended in to permit rectangular sealed-beam headlamps, these were placed in horizontally arrayed or vertically stacked pairs. By , the majority of new cars in the US market were equipped with rectangular lamps.
In , granting a 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. 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 rather than the internationalized European safety standards used outside North America. Nevertheless, this change to US regulations made it possible for headlamp styling in the US market to move closer to that in Europe.
They were mounted in the front fenders, which were smooth until the lights were cranked out—each with its own small dash-mounted crank—by the operator.
They aided aerodynamics when the headlamps were not in use, and were among the Cord's signature design features. Later hidden headlamps require one or more vacuum-operated servos and reservoirs, with associated plumbing and linkage, or electric motors , geartrains 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 s and s 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 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 Jaguar XJ The door mechanism may be actuated by vacuum pots, as on some Ford vehicles of the late s through early s such as the — Mercury Cougar , or by an electric motor as on various Chrysler products of the middle s through late s such as the — Dodge Charger.
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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 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 , rain and snow due to the retroreflection of the water droplets. 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 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. 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. Most low-beam headlamps are specifically designed for use on only one side of the road. 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. 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.
Some countries require automobiles to be equipped with daytime running lights 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 can be provided by the headlamps, the fog lamps , steady-lit operation of the front turn signals , or by special daytime running lamps. 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 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. In North America, the design, performance and installation of all motor vehicle lighting devices are regulated by Federal and Canada Motor Vehicle Safety Standard , which incorporates SAE 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 and , and other countries such as Japan, United Kingdom and Australia also made extensive use of sealed beams.
Headlamps must be kept in proper aim. This gives vehicles with high-mounted headlamps a seeing distance advantage, at the cost of increased glare to drivers in lower vehicles.