A headlamp is a lamp, usually attached to the front of a vehicle such as a car, with the purpose of illuminating the road ahead during periods of low visibility, such as night or precipitation. While it is common for the term headlight to be used interchangeably in informal discussion, headlamp is the technically correct term for the device itself, while headlight properly refers to the beam of light produced and distributed by the device.
"Dipping" (low beam) headlamps were introduced in 1915 by the Guide Lamp Company, but the 1917 Cadillac system allowed the light to be dipped with 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 was introduced and became standard for much of the century. The last vehicle with a foot-operated dimmer switch was the 1991 Ford F-Series. Foglamps were new for 1938 Cadillacs, and their 1954 "Autronic Eye" system automated the switch between high and low beams.
The standardized 7 in (178 mm) round sealed beam headlamp was introduced in 1940, and was soon required for all vehicles sold in the United States. Britain, Australia and other Commonwealth countries, as well as Japan, also made extensive use of 7 in. sealed beams. With some exceptions from Volvo and Saab, this headlamp size format was never widely accepted in Europe, leading to different front-end designs for each side of the Atlantic for decades.
The first halogen headlamp for vehicle use was introduced in 1962 by a consortium of European bulb and headlamp makers. Halogen technology makes incandescent filaments more efficient and can produce more light than from non-halogen filaments at the same power consumption. These were prohibited in the US, where non-halogen sealed beam lamps were required until 1978. From 1978 to 1983, all halogen headlamps in the U.S. were sealed beams with halogen bulbs inside. These halogen sealed beams remain available, 25 years after replaceable-bulb headlamps returned to the US in 1983.
High-intensity discharge systems were introduced in 1991's BMW 7-series. European and Japanese markets began to prefer HID headlamps, with as much as 50% market share in those markets, but they found slow adoption in North America. 1996's Lincoln Mark VIII was an early American effort at HIDs, and was the first and only car with DC HIDs.
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. Early headlamps were round, because that is the easiest shape for parabolic reflector manufacture.
There was no requirement in Europe for headlamps of standardised size or shape. Automakers were free to design their lamps to whatever shapes and sizes they wished, as long as the lamps met the engineering and performance requirements contained in the applicable European safety standards. That design freedom permitted the development of rectangular headlamps, first used in 1961. Developed by Cibié for the Citroën Ami 6 and by Hella for the German Ford Taunus, 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.
In 1940, the US government mandated a system of two 7 in. (178 mm) round sealed beam headlamps on all vehicles. Headlamp styling in the United States virtually ceased for many decades after this event.
A system of four round lamps, rather than two—one high/low and one high-beam 5¾ in. (146 mm) sealed beam on each side—were introduced in 1952 when the Prevost Car company included them in its Citaden bus model. Cadillac, Chrysler and Nash placed them in some of their car models in states that permitted the new system for the 1957 model year, and other American marques followed suit when all states permitted quad lamps in 1958. These lamps had some photometric advantages, but the primary advantage was the styling novelty permitted by the use of two small rather than one large lamp per side of the vehicle. The freedom was not absolute, however. 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. No such designs reached volume production. Most cars had their headlights in pairs side by side on each side of the car. Some Oldsmobiles had a parking light in the middle of each pair.
Also popular was an arrangement in which the two headlamps on each side were stacked, low beams above high beams. Nash 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. The Mercedes-Benz W100, W108, W111, and W112 models sold in America used this arrangement because their home-market composite lamps were illegal in the US. The British firm Alvis and the French firm FACEL also used this setup for some of their cars, as did Nissan in Japan.
In the late 1950s and early 1960s, Lincoln, Buick, and Chrysler arranged the headlamps diagonally by placing the low-beam lamps outboard and above the high-beam lamps. Certain British cars used a less extreme diagonal arrangement, with the inboard high-beam lamps placed only slightly lower than the outboard low-beam units. The 1965 Gordon-Keeble, Triumph Vitesse and Bentley S3 Continental used such an arrangement. (source: World Car Catalog)
In 1968 the U.S. DOT prohibited any decorative or protective element in front of the headlamps whenever the headlamps are switched on. Glass-covered headlamps, used on e.g. 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 imported with uncovered headlamps for the US market. This change meant that vehicles designed for good aerodynamic performance could not achieve it for the US market.
When Federal Motor Vehicle Safety Standard 108 was amended in the early 1970s to permit rectangular headlamps, these were placed in horizontally-arrayed or vertically-stacked pairs. By 1979, the majority of new cars in the US market were equipped with rectangular lamps. Again, the US permitted only two standardized sizes of rectangular sealed-beam lamp: A system of two 200 mm × 142 mm (7½ in. × 5½ in.) high/low beam units corresponding to the existing 7-inch round format, or a system of four 165 mm x 100 mm (6½ in. × 4 in.) units, two high/low and two high-beam, corresponding to the existing 5¾-inch (146 mm) round format.
In the late 1990s, round headlamps returned to popularity on new cars. These are generally not the discrete self-contained round lamps as found on older cars (certain Jaguars excepted), but rather involve circular or oval optical elements within an architecturally-shaped housing assembly.
Hidden headlamps were introduced in 1936, on the Cord 810. They were mounted in the front fenders, which were smooth until the lights were cranked out, each with its own small dash-mounted crank. They aided aerodynamics when the headlamps were not in use, and were among the Cord's signature design features.
Many notable cars used this feature, but no current volume-produced car models use hidden headlamps, because they present difficulties in complying with pedestrian-protection provisions recently added to international auto safety regulations, and because the mechanisms are costly and heavy. 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 early hidden headlamps, such as those on the Saab Sonett III, used a lever-operated mechanical linkage to raise the headlamps into position. Current market demands place a premium on vehicles' aerodynamic performance with lamps off and on, further reducing the attractiveness of pop-up headlamps. In addition, recent ECE regulations contain standards 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 door mechanism may be actuated by vacuum pots, as on some Ford vehicles of the late 1960s through early 1980s such as the 1967-1969 Mercury Cougar, or by an electric motor as on various Chrysler products of the middle 1960s through late 1970s such as the 1966-1967 Dodge Charger.
Low beam (dipped beam, passing beam, meeting beam) headlamps provide a distribution of light designed to provide adequate 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. 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 beam standard contained in FMVSS / CMVSS 108 .
High beam (main beam, driving beam, full beam) headlamps provide a bright, centre-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.
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, most countries require all vehicles registered or used on a permanent or semipermanent 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 usually illegal.
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: U.S. 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 benefit to either SAE or ECE beams; the two systems' acceptance and rejection by various countries is based primarily on inertial and philosophical grounds.,
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 technical standards. Elsewhere in the world, ECE internationalised 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 on new vehicles must produce white light, according to both ECE and SAE standards. Previous ECE regulations also permitted selective yellow light, which from 1936 until 1993 was required on all vehicles registered in France. Yellow headlamps are no longer required anywhere, but remain permitted in France, Belgium, The Netherlands, Switzerland, Japan, New Zealand, and some other countries.
Headlamps must be kept in proper alignment (or "aim"). Regulations for aim vary from country to country and from beam specification to beam specification. US SAE 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. ECE headlamps' aim angle is linked to headlamp mounting height. This gives all vehicles roughly equal seeing distance and all drivers roughly equal glare.
A light source (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 then shift parts of the light laterally and vertically to provide the required light distribution pattern. The lens may use both refraction and TIR to achieve the desired results. Most sealed-beam headlamps have lens optics.
Starting in the 1980s, CAD technology allowed the development of reflector headlamps with nonparabolic, complex-shape reflectors. First made by Valeo under their Cibié brand, these headlamps would revolutionize automobile design. The 1987 Dodge Monaco/Eagle Premier was the first U.S.-market car with complex-reflector headlamps, while the 1990 Honda Accord was the first U.S.-market car with such headlamps employing a completely clear, nonfaceted front lens.
The optics to distribute the light in the desired pattern are designed into the reflector itself, called an "optic reflector". 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 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.
Optic reflectors are commonly made of compression-moulded or injection molded plastic, though glass and metal optic reflectors also exist. The reflective surface is vapor deposited aluminum with a clear overcoating to prevent the extremely thin aluminum from oxidizing. Extremely tight tolerances must be maintained in the design and production of complex-reflector headlamps.
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.
The opposite tactic has also been employed in certain 2-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.
This system was first used with the Bilux/Duplo R2 bulb of 1954, and later with the halogen H4 bulb of 1971. In 1992, U.S. regulations were amended to permit the use of H4-style bulbs. Named HB2 or 9003, for the U.S. market, and with slightly different production tolerances stipulated, these bulbs are physically and electrically interchangeable with H4 bulbs. Similar optical techniques are used, but with different reflector and/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.
In this system a filament is located at one focus of an ellipsoidal reflector and has a condenser lens 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, determines the shape and sharpness of the cutoff. The shade may have a solenoid actuated pivot to provide both low and high beam — the shade is removed from the light path to create high beam, and placed in the light path to create low beam, and such optics are known as BiXenon or BiHalogen projectors, depending on the light source used. If there is no such arrangement, the cutoff shade is fixed in the light path, in which case separate high-beam lamps are required. The condenser lens may have slight fresnel rings or other surface treatments to reduce cutoff sharpness. Recent condenser lenses incorporate optical features specifically designed to direct some light upward towards the locations of retroreflective overhead road signs.
Hella introduced its "projector beam" optics for acetylene headlamps in 1911, but following the electrification of vehicle lighting, this optical technology wasn't used for many decades. The first modern polyellipsoidal automotive lamp was the Super-Lite, an auxiliary headlamp produced in a joint venture between Chrysler Corporation and Sylvania and optionally installed in 1969 and 1970 full-size Dodge 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 first appeared in 1981 on the Audi Quartz, the Audi Quattro-based concept car designed by Pininfarina for Geneva Auto Salon. Developed more or less simultaneously in Germany by Hella 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 version of the 1986 BMW 7 Series sold outside North America was the first volume-production auto to use polyellipsoidal low beam headlamps.
The first halogen bulb for vehicle use, the H1, was introduced in 1962 by a consortium of European bulb and headlamp makers. This bulb has a single axial filament that consumes 55 watts at 12.0 volts, 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 foglamp and driving lamps, as does H3. The H2 does not see wide use any more because 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). The use of H1 and H3 bulbs was legalized in the United States in 1997. 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 a low and a high beam with only one bulb), the H4, was released in 1971. The U.S. prohibited halogen headlamps until 1978, when halogen sealed beams were released. To this day, the H4 is still not legal for automotive use in the United States. Instead, the Americans created their own very similar standard (HB2/9003). The primary differences are that the HB2 sets more strict requirements on filament positioning, and that the HB2 are required to meet the lower maximum output standards set forth by the United States government.
The first U.S. halogen headlamp bulb, introduced in 1983, was the 9004/HB1. 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 U.S. approved halogen bulbs include the 9005/HB3 (65 W, 12.8 V), 9006/HB4 (55 W, 12.8 V), and 9007/HB5 (65/55 watts, 12.8 V).
HID stands for high-intensity discharge, a technical term for the electric arc that produces the light. The high intensity of the arc comes from metallic salts that are vapourised within the arc chamber. These lamps are formally known as gas-discharge burners, and produce more light for a given level of power consumption than ordinary tungsten and tungsten-halogen bulbs. Because of the increased amounts of light available from HID burners 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 xenon headlamp can produce a more robust beam pattern.
Automotive HID lamps are commonly called 'xenon headlamps', though they are actually metal halide lamps that contain xenon gas. The xenon gas allows the lamps to produce minimally adequate light immediately upon powerup, and accelerates the lamps' run-up time. If argon were used instead, as is commonly done in street lights and other stationary metal halide lamp applications, it would take several minutes for the lamps to reach their full output. The light from HID headlamps has a distinct bluish tint when compared with tungsten-filament headlamps.
Current-production burner 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 (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 lenses and reflector hardcoats. "S" burners — D1S, D2S, D3S, and D4S — have a plain glass shield and are primarily used in projector-type optics. "R" burners — 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 burners do emit considerable near-UV light, despite the shield.
Automotive headlamp applications using LEDs have been undergoing very active development since 2004. The first series-production LED headlamps are factory-installed on the 2008 Lexus LS 600h / LS 600h L (low beam, front position light and sidemarker only; high beam and turnsignal are filament based. The headlamp is supplied by Koito), and on the version of the 2008 Audi R8 sports car sold outside North America supplied by Automotive Lighting. The LED headlamp supplied by Hella for the 2009 Escalade Platinum is the first U.S. market headlamp with both a LED low and high beam. Present designs give performance between halogen and HID headlamps, with system power consumption slightly higher than halogen headlamps. These lamps currently require large packaging and a large number of the most powerful LED emitters available. As LED technology continues to evolve, the performance of LED headlamps is predicted to improve to approach, meet, and perhaps one day surpass that of HID headlamps.
The limiting factors with LED headlamps presently include high system expense, regulatory delays and uncertainty, glare concerns related to the output spectrum of white LEDs, and logistical issues created by LED operating characteristics. LEDs are commonly considered to be low-heat devices due to the public's familiarity with small, low-output LEDs used for electronic control panels and other applications requiring only modest amounts of light. However, LEDs actually produce a significant amount of heat per unit of light output. Rather than being emitted together with the light as is the case with conventional light sources, an LED's heat is produced at the rear of the emitters. The cumulative heat of numerous high-output LED emitters operating for prolonged periods poses thermal-management challenges for plastic headlamp housings. In addition, this heat buildup materially reduces the light output of the emitters themselves. LEDs are quite temperature sensitive, with many types producing at 30 °C (85 °F) only 60% of the rated light output they produce at an emitter junction temperature 16 °C (60 °F). Prolonged operation above the maximum junction temperature will permanently degrade the LED emitter and ultimately shorten the device's life. The need to keep LED junction temperatures low at high power levels always requires additional thermal management measures such as heatsinks and exhaust fans which are typically quite expensive.
Additional facets of the thermal issues with LED headlamps reveal themselves in cold ambient temperatures. Many types of LEDs produce at -12 °C (10 °F) up to 160% of their 16 °C (60 °F) rated output. The temperature-dependency of LED's light output creates serious challenges for the engineering and regulation of automotive lighting devices, which are in some cases required to produce intensities within a range smaller than the variation in LED output with temperatures normally experienced in automotive service.
Cold weather also brings another thermal-management conundrum: Not only must heat be removed from the rear of the headlamp so that the housing does not deform or melt and the emitters' output does not drop excessively, but heat must in addition be effectively applied to thaw snow and ice from the front lenses, which are not heated by the comparatively small amount of infared radiation emitted forward with the light from LEDs.
LEDs are increasingly being adopted for signalling functions such as parking lamps, brake lamps and turn signals as well as daytime running lamps, as in those applications they offer significant advantages over filament bulbs with fewer engineering challenges than headlamps pose.
These provide improved lighting for cornering. Some automobiles have their headlamps connected to the steering mechanism so the lights will follow the movement of the front wheels. Czech Tatra and 1920s Cadillacs were 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 headlamps' horizontal and vertical positioning in response to inputs from the vehicle's steering and suspension systems, though US regulations required this system to be removed from those models when sold in the USA.
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) lenses can become cloudy and discolored. 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 can buy a small amount of time, but doing so removes the protective coating from the lens, which when so stripped will deteriorate faster and more severely.
The reflector, made out of vaporized aluminum deposited in an extremely thin on a metal, glass or plastic substrate, can become oxidized or burnt and lose its specular reflective properties. This can happen if water enters the headlamp, if bulbs of higher wattage than specified are used, or simply with age and use. If the reflector when viewed by itself is not mirror-perfect, the headlamp should be replaced, for reflectors cannot effectively be restored.
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 ECE 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 as standard or available as optional equipment even where the headlamp specifications and/or prevailing technical regulations do not require them. North America, for example, does not use ECE 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 wiper blade or brush conceptually similar to those used on the windshield of the car, or a fixed or pop-up high-pressure sprayer which cleans the lenses with a spray of windshield washer fluid.
Assessing the Short-Term Forecast Capability of Nonstandardized Surface Observations Using the National Digital Forecast Database (NDFD)
Jul 01, 2010; ABSTRACT The number of surface observations from nonstandardized networks across the United States has appreciably...
Standard issue: antiquated, nonstandardized pool codes are causing confusion among operators--and may be putting public safety at risk.
Oct 01, 2003; During the peak of this year's swim season, the Centers for Disease Control released a seemingly frightening report that made the...
Moving toward ISDN interoperability. (ISDN interface devices in a nonstandardized industry) (Technology Information)
Sep 01, 1997; There is a wide and varying array of ISDN services and products waiting to service today's band-width-hungry road warriors and...