Headlamp
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.
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 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 or a small generator like a bottle 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
Acetylene Gas headlamp
The earliest headlamps, fuelled by combustible gas such as acetylene gas or oil, operated from the late 1880s. Acetylene gas lamps were popular in 1900s because the flame is resistant to wind and rain. The gas is ignited manually. 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, 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 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 integrated their vehicle's Delco electrical ignition and lighting system, forming the modern vehicle electrical system.
The Guide Lamp Company introduced "dipping" 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 and high 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 and E-Series vans. Fog lamps were new for 1938 Cadillacs, and their 1952 "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 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 sealed beams were permitted as well.
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 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 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 sealed beams dominate the sealed-beam market, which has declined steeply since replaceable-bulb headlamps were permitted in 1983.
High-intensity discharge systems appeared in the early 1990s, first in the BMW 7 Series. 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. 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. Rectangular headlamps were first used in 1960, developed by Hella for the German Ford Taunus P3 and by Cibié 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, 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 illuminated only 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 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 used this arrangement in the 1957 model year. Pontiac used this design starting in the 1963 model year; American Motors, Ford, Cadillac, and Chrysler 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, and Chrysler cars had the headlamps arranged diagonally with the low-beam lamps outboard and above the high-beam lamps. British cars, including the Gordon-Keeble, Jensen CV8, Triumph Vitesse, and Bentley S3 Continental, used such an arrangement as well.
In 1968, the newly initiated Federal Motor Vehicle Safety Standard 108 required all vehicles to have either the twin or quad round sealed beam headlamp system and prohibited any decorative or protective element in front of an operating headlamp. Glass-covered headlamps like those used on the Jaguar E-Type, pre-1968 VW Beetle, 1965 Chrysler and Imperial models, Porsche 356, Citroën DS, and Ferrari Daytona were no longer permitted, and vehicles had to be equipped with uncovered headlamps for the US market. This made it difficult for vehicles with headlamp configurations designed for good aerodynamic performance to achieve it in their US-market configurations.
The FMVSS 108 was amended in 1974 to permit rectangular 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.