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 United States 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 dynamo 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. Some carriages used oil lamp and Kerosene lamp for lighting.
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 produced bright white light that was 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" (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 and E-Series [Econoline] 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 7-inch (178 mm) 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 5.75-inch (146 mm) 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. As of 2010 halogen sealed beams dominate the sealed-beam market, which has declined steeply since replaceable-bulb headlamps were permitted in 1983. High-intensity discharge (HID) 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.
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