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lighting system of a motor vehicle consists of lighting and signalling devices mounted or integrated to the front, sides and rear of the vehicle. The purpose of this system is to provide illumination for the driver to operate the vehicle safely after dark, to increase the conspicuity of the vehicle, and to display information about the vehicle"s presence, position, size, direction of travel, and driver"s intentions regarding direction and speed of travel.

* 1 Colour of light emitted
* 2 Forward illumination
o 2.1 Headlamps
+ 2.1.1 Dipped beam (low beam, passing beam, meeting beam)
+ 2.1.2 Main beam (high beam, driving beam, full beam)
o 2.2 Auxiliary lamps
+ 2.2.1 Driving lamps
+ 2.2.2 Rallye and off-road lamps
+ 2.2.3 Front fog lamps
+ 2.2.4 Cornering lamps
+ 2.2.5 Spot lights
* 3 Conspicuity, signal and identification lights
o 3.1 Front
+ 3.1.1 Front position lamps (parking lamps)
+ 3.1.2 Daytime running lamps
+ 3.1.3 Dim-Dip Lamps (UK Only)
o 3.2 Lateral
+ 3.2.1 Sidemarker lights
+ 3.2.2 Turn signals
# Side turn signals
# Electrical connection and switching
# Turn signal colour
* Colour durability
# Sequential turn signals
o 3.3 Rear
+ 3.3.1 Rear position lamps (tail lamps)
+ 3.3.2 Rear fog lamps
+ 3.3.3 Stop lamps (brake lamps)
+ 3.3.4 Centre High Mount Stop Lamp (CHMSL)
# History
+ 3.3.5 Reversing lamps
+ 3.3.6 Rear registration plate lamp
o 3.4 Emergency warning devices
+ 3.4.1 Hazard flashers
+ 3.4.2 Emergency Braking Display
o 3.5 Retroreflectors
o 3.6 Experimental systems
+ 3.6.1 Multicolour auxiliary signals
o 3.7 Research and development
* 4 Convenience lights
* 5 On service vehicles
o 5.1 Emergency vehicle lights
o 5.2 Taxi displays
* 6 Construction and technology
o 6.1 Light sources
+ 6.1.1 Incandescent light bulbs
+ 6.1.2 Halogen
+ 6.1.3 Xenon
+ 6.1.4 Neon tubes
+ 6.1.5 Light emitting diodes (LED)
o 6.2 Variable-intensity signal lamps
* 7 See also
* 8 References
* 9 External links

[edit] Colour of light emitted
Extensively redundant rear lighting installation on a Thai tour bus

The colour of light emitted by vehicle lights is largely standardised by longstanding convention, first codified in the 1949 Vienna Convention on Road Traffic[1] and later specified in the 1968 United Nations Convention on Road Traffic.[2] Generally, but with some global and regional exceptions, lamps facing rearward must emit red light, lamps facing sideward and all turn signals must emit amber light, lamps facing frontward must emit white or selective yellow light, and no other colours are permitted except on emergency vehicles.

[edit] Forward illumination

Forward illumination is provided by high- ("main", "full", "driving") and low- ("dip", "dipped", "passing") beam headlamps, which may be augmented by auxiliary fog lamps, driving lamps, and/or cornering lamps.

[edit] Headlamps
Main article: Headlamp

[edit] Dipped beam (low beam, passing beam, meeting beam)

Dipped-beam (also called low, passing, or meeting beam) headlamps provide a light distribution to give adequate forward and lateral illumination without blinding other road users with excessive glare. This beam is specified for use whenever other vehicles are present ahead. The international ECE Regulations for 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.[3][4] Control of glare is less strict in the North American SAE beam standard contained in FMVSS / CMVSS 108.[5]

[edit] Main beam (high beam, driving beam, full beam)

Main-beam (also called high, driving, or full beam) headlamps provide an intense, centre-weighted distribution of light with no particular control of glare. Therefore, 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[6]

[edit] Auxiliary lamps

[edit] Driving lamps
High beam headlamps augmented by auxiliary driving lamps

"Driving lamp" is a term deriving from the early days of nighttime driving, when it was relatively rare to encounter an opposing vehicle. Only on those occasions when opposing drivers passed each other would the dipped or "passing" beam be used. The full beam was therefore known as the driving beam, and this terminology is still found in international ECE Regulations, which do not distinguish between a vehicle"s primary (mandatory) and auxiliary (optional) upper/driving beam lamps.[3][4][7] The "driving beam" term has been supplanted in North American regulations by the functionally descriptive term auxiliary high-beam lamp.[8] They are most notably fitted on rallying cars, and are occasionally fitted to production vehicles derived from or imitating such cars. They are common in countries with large stretches of unlit roads, or in regions such as the Nordic countries where the period of daylight is short during winter. Many countries regulate the installation and use of driving lamps. For example, in Russia each vehicle may have no more than three pairs of lights including the original-equipment items, and in Paraguay, auxiliary driving lamps must be off and covered with opaque material when the vehicle is circulating in urban areas.[9]

[edit] Rallye and off-road lamps

Vehicles used in rallying, off-roading, or at very high speeds often have extra lamps to broaden and extend the field of illumination in front of the vehicle. On off-road vehicles in particular, these additional lamps are sometimes mounted along with forward-facing lights on a bar (commonly referred to as a light bar) above the roof, which protects them from road hazards and raises the beams allowing for a greater projection of light forward.

[edit] Front fog lamps
A pair of yellow fog lamps

Front fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top, and are generally aimed and mounted low.[10][11][12] They may be either white or selective yellow. They are intended for use at low speed to increase the illumination directed towards the road surface and verges in conditions of poor visibility due to rain, fog, dust or snow. As such, they are often most effectively used in place of dipped-beam headlamps, reducing the glareback from fog or falling snow, although the legality varies by jurisdiction of using front fog lamps without low beam headlamps.

Use of the front fog lamps when visibility is not seriously reduced is often prohibited (for example in the United Kingdom), as they can cause increased glare to other drivers, particularly in wet pavement conditions, as well as harming the driver"s own vision due to excessive foreground illumination.[13]

The respective purposes of front fog lamps and driving lamps are often confused, due in part to the misconception that fog lamps are necessarily selective yellow, while any auxiliary lamp that makes white light is a driving lamp. Automakers and aftermarket parts and accessories suppliers frequently refer interchangeably to "fog lamps" and "driving lamps" (or "fog/driving lamps"). In most countries, weather conditions rarely necessitate the use of fog lamps, and there is no legal requirement for them, so their primary purpose is frequently cosmetic. They are often available as optional extras or only on higher trim levels of many cars. Studies have shown that in North America more people inappropriately use their fog lamps in dry weather than use them properly in poor weather.[14]

[edit] Cornering lamps
A cornering lamp on a 1983 Oldsmobile 98.

On some models, white cornering lamps provide extra lateral illumination in the direction of an intended turn or lane change. These are actuated in conjunction with the turn signals, though they burn steadily, and they may also be wired to illuminate when the vehicle is shifted into reverse gear, such as on many Saabs and Corvettes. North American technical standards contain provisions for front cornering lamps[15] as well as for rear cornering lamps.[16] Cornering lamps have traditionally been prohibited under international ECE Regulations, though provisions have recently been made to allow them as long as they are only operable when the vehicle is travelling at less than 40 kilometres per hour (about 25 mph),[17][18]

[edit] Spot lights

Police cars, emergency vehicles, and those competing in road rallies are sometimes equipped with an auxiliary lamp, sometimes called an alley light, in a swivel-mounted housing attached to one or both a-pillars, directable by a handle protruding through the pillar into the vehicle. Until the mid-1940s, these spot lamps could be found as standard equipment on expensive cars. Until the mid-1960s, they were commonly offered by automakers as model-specific accessory items. More recently, customizers have installed them or dummy substitutes on their cars. Spot lamps are used to illuminate signs, house numbers, and people with more power than a flashlight. Spot lights can also be had in versions designed to mount through the vehicle"s roof. In some countries, for example in Russia, spot lights are allowed only on emergency vehicles or for off-road driving only.

[edit] Conspicuity, signal and identification lights
A North American 1991 Acura Integra with parking lamps, hazard flashers, fog lights and sidemarker lamps illuminated

Conspicuity devices are the lamps and reflectors that make a vehicle conspicuous and visible with respect to its presence, position, direction of travel, change in direction or deceleration. Such lamps may burn steadily, blink, or flash, depending on their intended and regulated function.
[edit] Front

[edit] Front position lamps (parking lamps)

Nighttime standing-vehicle conspicuity to the front is provided by front position lamps, known as parking lamps or parking lights in North America, front sidelights in UK English, and in other regions as position lamps, standing lamps, or city lights. Despite the UK term, these are not the same as the sidemarker lights described below. The front position lamps may emit white or amber light in North America; elsewhere in the world they must emit only white light. The city light terminology for front position lamps comes from the now obsolete practice, formerly adhered to in cities like Moscow, London and Paris, of driving at night in built-up areas using these low-intensity lights rather than headlamps. It is now illegal in most countries to drive a vehicle with parking lamps illuminated, unless the headlamps are also illuminated. The UK briefly required Dim-Dip lights, described below, in an attempt to optimize the level of light used at night in built-up areas.
Parking lamps on a Soviet 1974 Volga GAZ-24. In Russia, they are called "podfarniki" ("under-headlights") or "gabarite lights".

Since the late 1960s, front position lamps have been required to remain illuminated even when the headlamps are on, to maintain the visual signature of a dual-track vehicle to oncoming drivers in the event of headlamp burnout. Front position lamps worldwide produce between 4 and 125 candelas.

In Germany, the StVZO (Road Traffic Licensing Regulations) calls for a different function also known as parking lamps: With the vehicle"s ignition switched off, the operator may activate a low-intensity light at the front (white or amber) and rear (red) on either the left or the right side of the car. This function is used when parking in narrow unlit streets to provide parked-vehicle conspicuity to approaching drivers. This function, which is optional under ECE and US regulations, is served passively and without power consumption in North America by the mandatory sidemarker retroreflectors.

[edit] Daytime running lamps
LED daytime running lights on Audi A4
Main article: Daytime running lamp

Some countries permit or require vehicles to be equipped with daytime running lamps (DRL). These may be functionally-dedicated lamps, or the function may be provided by e.g. the low beam or high beam headlamps, the front turn signals, or the front fog lamps, depending on local regulations. In ECE Regulations, a functionally-dedicated DRL must emit white light with an intensity of at least 400 candelas on axis and no more than 800 candelas in any direction. Most countries applying ECE Regulations permit low beam headlamps to be used as daytime running lamps. Canada, Sweden, Norway, Slovenia, Finland, Iceland, and Denmark require hardwired automatic DRL systems of varying specification depending on the specific country. DRLs are permitted in many countries where they are not required, but prohibited in other countries not requiring them.

In North America, daytime running lamps may produce up to 7,000 candelas, and can be implemented as high-beam headlamps running at less-than-rated voltage. This has provoked a large number of complaints about glare.[19][20]

Front, side, and rear position lamps are permitted, required or forbidden to illuminate in combination with daytime running lamps, depending on the jurisdiction and the DRL implementation.

[edit] Dim-Dip Lamps (UK Only)

UK regulations briefly required vehicles first used on or after 1 April 1987 to be equipped with a dim-dip device[21] or special running lamps, except such vehicles as comply fully with ECE Regulation 48 regarding installation of lighting equipment. A dim-dip device operates the low beam headlamps (called "dipped beam" in the UK) at between 10% and 20% of normal low-beam intensity. The running lamps permitted as an alternative to dim-dip were required to emit at least 200 candelas straight ahead, and no more than 800 candelas in any direction. In practice, most vehicles were equipped with the dim-dip option rather than the running lamps.

The dim-dip systems were not intended for daytime use as DRLs. Rather, they operated if the engine was running and the driver switched on the parking lamps (called "sidelights" in the UK). Dim-dip was intended to provide a nighttime "town beam" with intensity between that of the parking lamps commonly used at the time by British drivers in city traffic after dark, and dipped (low) beams; the former were considered insufficiently intense to provide improved conspicuity in conditions requiring it, while the latter were considered too glaring for safe use in built-up areas. The UK was the only country to require such dim-dip systems, though vehicles so equipped were sold in other Commonwealth countries with left-hand traffic.[22]

In 1988, the European Commission successfully prosecuted the UK government in the European Court of Justice, arguing that the UK requirement for dim-dip was illegal under EC directives prohibiting member states from enacting vehicle lighting requirements not contained in pan-European EC directives. As a result, the UK requirement for dim-dip was quashed. Nevertheless, dim-dip was (and is) still permitted, and while such systems are not presently as common as they once were, dim-dip functionality was fitted on many new cars well into the 1990s.

[edit] Lateral

[edit] Sidemarker lights
Chevrolet Corvette Z06 in Germany with amber rear sidemarker

In North America, amber front and red rear sidemarker lamps and retro-reflectors are required. The law initially required lights or retroreflectors on vehicles made after 1 January 1968. This was amended to require lights and retroreflectors on vehicles made after 1 January 1970. These side-facing devices make the vehicle"s presence, position and direction of travel clearly visible from oblique angles. The lights are wired so as to illuminate whenever the vehicles" parking and taillamps are on, including when the headlamps are being used. Front amber sidemarkers in North America may or may not be wired so as to flash in sync with the turn signals.[23] Sidemarkers are permitted outside North America, but not required. If installed, they are required to be brighter and visible through a larger horizontal angle than US sidemarkers, they may not flash, and they must be amber at the front and rear unless the rear sidemarker is incorporated into the main rear lamp cluster, in which case it may be red or amber. Some Japanese, European, British and US-brand vehicles have sidemarkers in Europe and other countries where they are not required.

Japan"s recent accession to internationalized ECE Regulations has caused automakers to change the rear sidemarker colour from red to amber on their models so equipped in the Japanese market.[24]

[edit] Turn signals
Vehicle with front turn signal and side repeater illuminated

Turn signals formally called directional indicators or directional signals, and informally known as "indicators", "directionals", "blinkers" or "flashers" are signal lights mounted near the left and right front and rear corners of a vehicle, and sometimes on the sides, used to indicate to other drivers that the operator intends a lateral change of position (turn or lane change). Electric turn signal lights were devised as early as 1907.[25] The modern turn signal was first generally offered by major automobile manufacturers in 1939. Today, turn signals are required on all vehicles that are driven on public roadways in most countries. Alternative systems of hand signals were used earlier, and they are still common for bicycles. Hand signals are also sometimes used when regular vehicle lights are malfunctioning.

Some cars from the 1920s to 1950s used retractable semaphores called trafficators rather than flashing lights. They were commonly mounted high up behind the front doors and swung out horizontally. However, they were fragile and could be easily broken off and also had a tendency to stick in the closed position.

As with all vehicle lighting and signalling devices, turn signal lights must comply with technical standards that stipulate minimum and maximum permissible intensity levels, minimum horizontal and vertical angles of visibility, and minimum illuminated surface area to ensure that they are visible at all relevant angles, do not dazzle those who view them, and are suitably conspicuous in conditions ranging from full darkness to full direct sunlight.

[edit] Side turn signals

In most countries outside North America, cars must be equipped with side-mounted turn signal repeaters to make the turn indication visible laterally rather than just to the front and rear of the vehicle. These are permitted, but not required in North America. As an alternative in North America, the front amber sidemarker lights may be wired to flash with the turn signals, but this also is not mandatory. In recent years, many automakers have been incorporating side turn signal devices into the sideview mirror housings, rather than mounting them on the vehicle"s fenders. One of the first vehicles so equipped was the Mercedes-Benz R170. There is evidence to suggest these mirror-mounted turn signals may be more effective than fender-mounted items.[26]

[edit] Electrical connection and switching
Two types of dashboard turn signal telltale indicators

Turn signals are required to blink on and off, or "flash", at a steady rate of between 60 and 120 blinks per minute. International regulations require that all turn signals activated at the same time (i.e., all right signals or all left signals) flash in simultaneous phase with one another; North American regulations permit sidemarkers wired for side turn signal functionality to flash in opposite-phase. Worldwide regulations stipulate an audiovisual telltale when the turn signals are activated; this usually takes the form of one combined or separate left and right green indicator lights on the vehicle"s instrument cluster, and a cyclical "tick-tock" noise generated electromechanically or electronically. It is also required that audio and/or visual warning be provided to the vehicle operator in the event of a turn signal"s failure to light. This warning is usually provided by a much faster- or slower-than-normal flash rate, visible on the dashboard indicator, and audible via the faster tick-tock sound.

Turn signals are in almost every case activated by means of a horizontal lever (or "stalk") protruding from the side of the steering column, though some vehicles have the lever mounted instead to the dashboard. The outboard end of the stalk is pushed clockwise to activate the right turn signals, or anticlockwise for the left turn signals. This operation is intuitive; for any given steering manoeuvre, the stalk is pivoted in the same direction as the steering wheel must be turned. In virtually all left-hand drive cars, the signal stalk is on the left side of the column. In right-hand drive cars, the signal stalk may be on either side.[citation needed] If the vehicle"s wipers are controlled by a stalk on the opposite side from the signal stalk, a driver unaccustomed to the vehicle may inadvertently activate the wrong control.

Virtually all vehicles have a turn indicator self-cancelling feature that returns the lever to the neutral (no signal) position as the steering wheel approaches the straight-ahead position after a turn has been made. Depending on the configuration of the steering and self-cancelling systems, large-radius turns may not involve enough steering wheel movement to trip the turn signal switch back to the neutral position automatically. However, if the self-cancelling system is configured to avoid this, it may tend to cancel the turn signal prematurely in response to normal steering wheel movement before and during common turns. Beginning in the late 1960s, indicating for a lane change was facilitated by the addition of a spring-loaded momentary signal-on position just shy of the left and right detents. The signal operates for however long the driver holds the lever partway towards the left or right turn signal detent. Some recent vehicles have an automatic lane-change indication feature; tapping the lever partway towards the left or right signal position and immediately releasing it causes the applicable turn indicators to flash three to five times.

Many transit buses, such as those in New York, have, since at least the 1950s, had turn signals activated by floor-mounted momentary-contact footswitches on the floor near the driver"s left foot (on left-hand drive buses). The foot-activated signals allow bus drivers to keep both hands on the steering wheel while watching the road and scanning for passengers as they approach a bus stop. New York City Transit bus drivers, among others, are trained to step continuously on the right directional switch while servicing a bus stop, to signal other road users they are intentionally dwelling at the stop, allowing following buses to skip that stop.[27] This method of signalling requires no special arrangements for self-cancellation or passing.

[edit] Turn signal colour
Soviet 1974 GAZ-24 Volga"s taillight with red stop lamp, amber turn signal and white reversing lamp

Until the early 1960s, most front turn signals worldwide emitted white light and most rear turn signals emitted red. Amber front turn signals were voluntarily adopted by the auto industry in the USA for most vehicles beginning in the 1963 model year, though front turn signals were still permitted to emit white light until FMVSS 108 took effect for the 1968 model year, whereupon amber became the only permissible colour for front turn signals. Presently, almost all countries outside North America require that all front, side and rear turn signals produce amber light. In North America the rear signals may be amber or red. International proponents of amber rear signals say they are more easily discernible as turn signals. U.S. studies in the early 1990s demonstrated improvements in the speed and accuracy of following drivers" reaction to brake lamps when the turn signals were amber rather than red.[28][29][30][31][32] American regulators and other proponents of red rear turn signals have historically asserted there is no proven lifesaving benefit to amber signals, though a 2008 U.S. study suggests vehicles with amber rear signals rather than red ones are up to 28% less likely to be involved in certain kinds of collisions.[33]

There is some evidence that turn signals with colourless clear lenses and amber bulbs may be less conspicuous in bright sunlight than those with amber lenses and colourless bulbs.[34]

[edit] Colour durability

The amber bulbs commonly used in turn signals with colourless lenses are no longer made with cadmium glass, for cadmium is banned due to its toxicity by various regulations worldwide, including the European RoHS directive.[35] Amber glass made without cadmium is very costly, so most amber bulbs are now made with clear glass dipped in an amber coating. Some of these coatings are not as durable as the bulbs themselves; with prolonged heat-cool cycles, the coating may flake off the bulb glass, or its colour may fade. This causes the turn signal to emit white light rather than the required amber light. The international regulation on motor vehicle bulbs requires manufacturers to test bulbs for colour endurance.[36] However, no test protocol or colour durability requirement is specified. Discussion is ongoing[37] within the Groupe des Rapporteurs d"clairage, the UNECE working group on vehicular lighting regulation, to develop and implement a colour durability standard. Rather than using an amber bulb, some signal lamps contain an inner amber plastic enclosure between a colourless bulb and the colourless outer lens.

[edit] Sequential turn signals

Sequential turn signals are a feature on some past-model cars whereby multiple lights that produce the rear turn signal do not all flash on and off in phase. Rather, the horizontally-arrayed lamps are illuminated sequentially: the innermost lamp lights and remains illuminated, the next outermost lamp lights and remains illuminated, followed by the next outermost lamp and so on until the outermost lamp lights briefly, at which point all lamps extinguish together and, after a short pause, the cycle begins again. The visual effect is one of outward motion in the direction of the intended turn or lane change. This implementation has generally been found only on American cars that use combination red rear brake and turn signal lamps.

Sequential turn signals were factory fitted to Ford Thunderbirds built between 1965 and 1971, inclusive, to Mercury Cougars between 1967 and 1973, to Shelby Mustangs between 1968 and 1970, and to 1969 Imperials (built by Chrysler). No other production cars were so equipped, initially due to the cost and complexity of the system. Federal Motor Vehicle Safety Standard 108, which regulates automotive lighting, was amended to require that all turn signal lamps operate in synchronized phase, thus prohibiting sequential turn signals.

Two different systems were employed. The earlier, fitted to the 1965 through 1968 Ford-built cars, was electro-mechanical, featuring an electric motor driving, through reduction gearing, a set of three slow-turning cams. These cams would actuate switches to turn on the lights in sequence so long as the turn signal switch was set. This system was complicated and prone to failure, and therefore the units are non-functional in many surviving cars.[citation needed]

Later Ford cars and the 1969 Chrysler Imperial used a transistorized control module with no moving parts; this was much more reliable[citation needed].

U.S. Federal and Canadian motor vehicle safety standards currently prohibit sequential turn signals. However, Federal standards do not apply to vehicles in use, and so extension of this prohibition to vehicles in use is left as a matter of choice for each state or province. Sequential turn signals are sometimes used on emergency vehicles.[citation needed]

However, Ford has announced sequential turn signals will be used on the 2010 Ford Mustang[38].

[edit] Rear

[edit] Rear position lamps (tail lamps)

Night time vehicle conspicuity to the rear is provided by rear position lamps (also called taillamps or tail lamps, taillights or tail lights, or in British English, rear sidelights). These are required to produce only red light, and to be wired such that they are lit whenever the front position lamps are illuminatedincluding when the headlamps are on. Rear position lamps may be combined with the vehicle"s brake lamps, or separate from them. In combined-function installations, the lamps produce brighter red light for the brake lamp function, and dimmer red light for the rear position lamp function. The tail and brake light functions may be produced separately and/or by a dual-intensity lamp.

Regulations worldwide stipulate minimum intensity ratios between the bright (brake) and dim (tail) modes, so that a vehicle displaying rear position lamps will not be mistakenly interpreted as showing brake lamps, and vice versa.

Many modern designs use LED lighting sources beginning in 1999 with the Cadillac Deville.[39]

[edit] Rear fog lamps
Rear fog lamps in the bumper of a European-spec Chevrolet Corvette

In Europe and other countries adhering to ECE Regulation 48, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which serve as high-intensity rear position lamps to be energised by the driver in conditions of poor visibility to enhance vehicle conspicuity from the rear. The allowable range of intensity for a rear fog lamp is 150 to 300 candelas, which is within the range of a U.S. brake lamp. For this reason, many European vehicles imported to the United States have their rear fog lamps wired as brake lamps, since their European-specification brake lamps may not be sufficiently intense to comply with U.S. regulations, and in North America rear fog lamps are not required equipment. However, they are permitted, and are found almost exclusively on European-brand vehicles in North America Audi, Jaguar, Mercedes, MINI, Land Rover, Saab and Volvo provide functional rear fog lights on their North American models. The final generation Oldsmobile Aurora also had dual rear fog lights installed in the rear bumper as standard equipment.

Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. If a single rear fog is fitted, most jurisdictions require it to be located at or to the driver"s side of the vehicle"s centreline whichever side is the prevailing driver"s side in the country in which the vehicle is registered. This is to maximise the sight line of following drivers to the rear fog lamp. If two rear fog lamps are fitted, they must be symmetrical with respect to the vehicle"s centreline. Proponents of twin rear fog lamps say two lamps provide vehicle distance information not available from a single lamp. Proponents of the single rear fog lamp say dual rear fog lamps closely mimic the appearance of illuminated brake lamps (which are mandatorily installed in pairs), reducing the conspicuity of the brake lamps" message when the rear fogs are activated. To provide some safeguard against rear fog lamps" masking of brake lamps, ECE R48 requires a separation of at least 10 cm between the closest illuminated edges of any brake lamp and any rear fog lamp.

[edit] Stop lamps (brake lamps)

Red steady-burning rear lights, brighter than the rear position lamps, are activated when the driver applies the vehicle"s brakes. These are called brake lights or stop lamps. They are required to be fitted in multiples of two, symmetrically at the left and right edges of the rear of every vehicle. Outside North America, the range of acceptable intensity for a brake lamp containing one light source (e.g. bulb) is 60 to 185 candelas. In North America, the acceptable range for a single-bulb brake lamp is 80 to 300 candelas.

[edit] Centre High Mount Stop Lamp (CHMSL)
LED CHMSL retrofitted on a 1974 Valiant

In North America since 1986, in Australia and New Zealand since 1990, and in Europe since 1998, a central brake lamp, mounted higher than the vehicle"s left and right brake lamps and called a Centre High Mount Stop Lamp (CHMSL), is also required. The CHMSL (pronounced /'t??mz?l/) is also sometimes referred to as the centre brake lamp, the third brake light, the eye-level brake lamp, the safety brake lamp, the high-level brake lamp, or the Liddy Light (for Elizabeth Dole, who as U.S. Secretary of Transportation presided over its introduction in the United States[40]). The CHMSL may produce light by means of a single central filament bulb, a row or cluster of filament bulbs or LEDs, or a strip of Neon tube.

The CHMSL is intended to provide a deceleration warning to following drivers whose view of the vehicle"s left and right stop lamps is blocked by interceding vehicles. It also helps to disambiguate brake vs. turn signal messages in North America, where red rear turn signals identical in appearance to brake lamps are permitted, and also can provide a redundant brake signal in the event of a brake lamp malfunction. The CHMSL is required to illuminate steadily; it is not permitted to flash except in certain cases under severe braking.

On passenger cars, the CHMSL may be placed above the back glass, affixed to the vehicle"s interior just inside the back glass, or it may be integrated into the vehicle"s deck lid or into a spoiler. Other specialised fitments are sometimes seen; the Land Rover Freelander has the CHMSL on a stalk fixed to the spare wheel carrier. Trucks, vans and commercial vehicles sometimes have the CHMSL mounted to the trailing edge of the vehicle"s roof. The CHMSL is required by regulations worldwide to be centred laterally on the vehicle, though ECE R48 permits lateral offset of up to 15 cm if the vehicle"s lateral centre is not coincident with a fixed body panel, but instead separates movable components such as doors. The Renault Master van, for example, uses a laterally offset CHMSL for this reason. The height of the CHMSL is also regulated, in absolute terms and with respect to the mounting height of the vehicle"s conventional left and right brake lamps. Depending on the left and right lamps" height, the CHMSL isn"t always mounted relatively very high; its lower edge may be just above the left and right lamps" upper edge.

[edit] History

The 19681971 Ford Thunderbird could be ordered with additional high-mounted brake and turn signal lights. These were fitted in strips on either side of its small rear window. This option was rarely specified.[citation needed] The Oldsmobile Toronado from 1971-1978, and the Buick Riviera from 1974-1976 had dual high-mounted supplemental brake lights/turn signals as standard, and were located just below the bottom of the rear window, visually aligned with the conventional rear tail lights/brake lights/turn signals just above the rear bumper. These innovations were not widely adopted at the time. Auto and lamp manufacturers in Germany experimented with dual high-mount supplemental brake lamps in the early 1980s, but this effort, too, failed to gain wide popular or regulatory support.

Early studies involving taxicabs and other fleet vehicles found that a third stop lamp reduced rear-end collisions by about 50%. The lamp"s novelty probably played a role, since today the lamp is credited with reducing collisions by about 5%. [41]

In 1986, the United States National Highway Traffic Safety Administration and Transport Canada mandated that all new passenger cars have a CHMSL installed. A CHMSL was required on all new light trucks and vans starting in 1994. CHMSLs are so inexpensive to incorporate into a vehicle that even if the lamps prevent only a few percent of rear end collisions they remain a cost-effective safety feature.

[edit] Reversing lamps
Illuminated reversing lamps on a Mercedes-Benz SLR McLaren

To provide illumination to the rear when backing up, and to warn adjacent vehicle operators and pedestrians of a vehicle"s rearward motion, each vehicle must be equipped with at least one rear-mounted, rear-facing reversing lamp (or "backup light"). These are currently required to produce white light by U.S. and international ECE regulations. However, some countries have at various times permitted amber reversing lamps. In Australia and New Zealand, for example, vehicle manufacturers were faced with the task of localizing American cars originally equipped with combination red brake/turn signal lamps and white reversing lamps. Those countries" regulations permitted the amber rear turn signals to burn steadily as reversing lamps, so automakers and importers were able to combine the (mandatorily amber) rear turn signal and (optionally amber) reversing lamp function, and so comply with the regulations without the need for additional lighting devices. Both Australia and New Zealand presently require white reversing lamps, so the combination amber turn/reverse lamp is no longer permitted on new vehicles.[42] The U.S. state of Washington presently permits reversing lamps to emit white or amber light.[43]

[edit] Rear registration plate lamp

The rear registration plate may be illuminated by a white lamp (which points at the plate); in some jurisdictions it is compulsory to have one of these and it must be illuminated whenever the normal marker lights must be.

[edit] Emergency warning devices

[edit] Hazard flashers

International regulations have since the 1960s[citation needed] required vehicles to be equipped with a control which, when activated, flashes the left and right directional signals, front and rear, all at the same time and in phase. This function is meant to be used to indicate a hazard such as a vehicle stopped in or alongside moving traffic, a disabled vehicle, an exceptionally slow-moving vehicle, or a vehicle participating in a motorcade. Operation of the hazard flashers must be via a control independent of the turn signal control, and audiovisual telltale must be provided to the driver. In vehicles with a separate left and right green turn signal indicator on the dashboard, both left and right indicators may flash to provide visual indication of the hazard flashers" operation. In vehicles with a single green turn signal indicator on the dashboard, a separate red indicator light must be provided for hazard flasher indication.

[edit] Emergency Braking Display

Mercedes-Benz, Volvo,[44] and BMW have released vehicles equipped with brake lamps having a standard appearance when the driver brakes normally, and a unique appearance when the driver applies the brakes rapidly and severely, as for example in an emergency. Mercedes" concept is to flash the brake lamps rapidly under heavy deceleration, Volvo makes the brake lamps brighter, and BMW is experimenting with brake lamps that "grow larger" under hard braking, through the use of additional lighted compartments not activated under normal braking.

The Volkswagen Group of manufacturers (VW, Audi,Seat & Skoda) also have a system on all newer models[vague] that will turn on the hazard flasher under braking conditions hard enough to activate the Emergency Brake Assist and/or ABS.

An experimental study at the University of Toronto [45] has tested brake lights which gradually and continuously grow in illuminated area with increasing vehicle deceleration rate (i.e., increasing brake application pressure).

The idea behind such emergency-braking indicator systems is to catch following drivers" attention with special urgency. However, there remains considerable debate over whether the system offers a measurable increase in safety performance. To date, studies of vehicles in service have not shown any significant such improvement. The systems used by BMW, Volvo, and Mercedes differ not only in operational mode (growing vs. intensifying vs. flashing, respectively), but also in such parameters as deceleration threshold of activation. Data are being collected and analyzed in an effort to determine how such a system might be implemented to maximize a safety benefit, if such a benefit can be realized with visual emergency braking displays. One potentially problematic factor in the implementation of flashing stop lamps in North America is that North American regulations permit flashing brake lamps to be used in lieu of separate rear turn signal and hazard warning lamps.

[edit] Retroreflectors

Retroreflectors (also reflex reflectors) produce no light of their own, but rather reflect incident light back towards its source, i.e., another driver"s headlight. They are regulated as automotive lighting devices, and specified so as to account for the separation between a vehicle"s headlamps and its driver"s eyes. Thus, vehicles are conspicuous even when their electrically-powered lighting system is deactivated or disabled. Regulations worldwide require each vehicle to be equipped with rear-facing red retroreflectors. North American regulations also require side-facing retroreflectors, amber in front and red in the rear. Sweden, South Africa and other countries have at various times required white front-facing retroreflectors.

[edit] Experimental systems

[edit] Multicolour auxiliary signals

Some jurisdictions, such as the US states of Oregon and Idaho, permit vehicles to be equipped with auxiliary rear signal systems displaying green light when the accelerator is depressed, yellow light when the vehicle is coasting, and red light when the brake is depressed.[46][47] Such systems have in the past been sold as aftermarket accessories, but are today seldom seen in traffic.

[edit] Research and development

The US National Highway Traffic Safety Administration, among other bodies, has commissioned studies of these and many other vehicle signal systems and configurations, in an effort to determine the most promising avenues and best practices for enhanced crash avoidance via optimised vehicle conspicuity and signal lighting systems.[48]

[edit] Convenience lights

Most cars have at least one dome light (UK, courtesy light) located in or near the ceiling of the passenger compartment, to provide illumination by which to fasten seatbelts and enter or exit the car. These often have an option to switch on when the front (or all) passenger doors are opened. Many vehicles have expanded this feature, causing the overhead interior light to remain on after all doors are closed, allowing passengers to fasten seat belts with added illumination. The extended lighting cycle usually ends when the vehicles ignition has begun, or a gradual reduction in light emitted after a couple of minutes if the car isn"t started. Interior lighting has been added on some vehicles at the bottom edge of the dashboard, which illuminate the floor for front passengers, or underneath the front seats at the rear, to illuminate the floor for rear seat passengers. This type of convenience lighting approach is also sometimes used to illuminate interior or exterior door handles, exterior step running boards, or electric window switches.

LED light sources are beginning to appear increasingly as interior convenience lights in various locations as the technology becomes more widely used.

There may be additional map lights that are aimed at specific passenger positions, that allow for reading. Some vehicles have approach lighting (puddle lights) integrated into the exterior mirrors or lower edges of the doors, as well as activating interior lighting, that is activated via key fob. Some high end cars feature "theater" interior illumination for glare-free interior visibility by night which does not distract the driver. Many cars have lights in the trunk (or boot), the engine compartment, and the glovebox and other storage compartments.

Most instruments and controls on a dashboard in modern vehicles are illuminated in some fashion when the headlamps are turned on, and the intensity of light can be adjusted by the driver for comfort. Saabs feature an aerospace technologies-derived "night panel" function which shuts off all interior illumination save for the speedometer to improve the driver"s night vision.

[edit] On service vehicles

[edit] Emergency vehicle lights
Main article: Emergency vehicle lighting
U.S. Police cruisers with lights flashing.
Light bar on an English police car.

Emergency vehicles such as fire engines, ambulances, police cars, snow-removal vehicles and tow trucks are usually equipped with intense warning lights of particular colours. These may be motorised rotating beacons, xenon strobes, or arrays of LEDs. The prescribed colours differ by jurisdiction; in most countries, blue and/or red special warning lamps are used on police, fire, and medical-emergency vehicles. In North America and some other jurisdictions, amber lights are for tow trucks, private security personnel, and other nonofficial special-service vehicles, while volunteer firefighters use red, blue, or green, depending on jurisdiction. In the UK, doctors may use green warning lamps. Special warning lights are also sometimes mounted on slow vehicles such as excavators and tractors.

[edit] Taxi displays

Taxicabs are distinguished by special lights according to local regulations. They may have an illuminated "Taxi" sign, a light to signal that they are ready to take passengers, and an emergency panic light the driver can activate in the event of a robbery to alert passersby to call the police.

[edit] Construction and technology
Light source placed in a parabolic reflector to achieve a directed beam

[edit] Light sources

[edit] Incandescent light bulbs

Traditionally, an incandescent tungsten light bulb has been the light source used in all of the various automotive signalling and marking lamps. Typically, bulbs of 21 to 27 watts, producing 280 to 570 lumens (22 to 45 Mean Spherical Candlepower) are used for brake, turn, reversing and rear fog lamps, while bulbs of 4 to 10 W, producing 40 to 130 lm (3 to 10 mscp) are used for tail lamps, parking lamps, sidemarker lamps and side turn signal repeaters.

[edit] Halogen

Tungsten-halogen light bulbs are a very common light source for headlamps and other forward illumination functions. Some recent-model vehicles use small halogen bulbs for exterior signalling and marking functions, as well. The first halogen lamp approved for automotive use was the H1, which was introduced in Europe in 1962.

[edit] Xenon
Main article: Headlamp

The devices popularly known as "Xenon headlamps" actually incorporate Metal halide light sources, and are known as high-intensity discharge, or HID lamps.

Xenon is currently the lamp used in single-source lighting systems being developed for automotive use. In these systems, a single light source sends light via optical fibers to wherever it is needed in the automobile. This development, known as distributive lighting, is already appearing in the interior lighting features, for example the Ford Mustang"s interior lighting. In an expanded system, the light could be channeled to the side mirrors for example, which would act as forward driving lights that could be made to swivel in position with the car as it turns. The headlight pattern would not be limited to individual overlapping beams, but could be channeled by electronic controls of the fiber optics to provide optimum visibility over an extended range of driving conditions including in the fog, dust or snow. Individual lamps would not be needed, just a mounting point for the optical fibers running back to the single light source and computer controlled for colour, intensity and continuity.[49][50]

[edit] Neon tubes
Lancia Thesis Neon Taillight

Neon lamp tubes were introduced into widespread production for the CHMSL on the 1995 Ford Explorer, and notable later uses included the 1998 Lincoln Mark VIII, with a neon tube spanning the width of the trunk decklid, and the BMW Z8, which made extensive use of neon. Numerous concept cars have included neon lamp features, from such manufacturers as Volvo. Hella offered an aftermarket neon CHMSL in the late 1990s.

The linear packaging of the neon light source lends itself to the linear packaging favored for many CHMSL installations, and neon lights offer the same nearly-instant rise time benefit as LEDs. However, neon tubes require an expensive and relatively power-hungry ballast (power supply unit), and as a result, neon lights have not found significant long-term popularity as sources of light for automotive signaling.

[edit] Light emitting diodes (LED)
Audi A6 Avant LED tail light

LEDs are being used with increasing frequency in automotive lamps. They offer very long service life, extreme vibration resistance, and can permit considerably shallower packaging compared to most bulb-type assemblies. LEDs also offer a significant safety performance benefit when employed in brake lights, for when power is applied they rise to full intensity approximately 200 milliseconds (0.2 seconds) faster than incandescent bulbs. This fast rise time not only improves the attentional conspicuity of the brake lamp, but also provides following drivers with increased time in which to react to the appearance of the brake lamps.

LEDs were first applied to automotive lighting in Centre High Mount Stop Lamps (CHMSL), beginning in the early 1990s. Adoption of LEDs for other signal functions on passenger cars has been slow, but is beginning to increase with demand for the technology and related styling updates. The 2007 Audi R8 sports car uses two strips of optically-focused high-intensity LEDs for its Daytime Running Lamps. Optional on the R8 in ECE markets is the world"s first LED headlamp made by AL-Automotive Lighting.[51] The low and high beams along with the position (parking) lamp and front turn signal are all realized with LEDs. The Lexus LS 600h features LED low beam, position and sidemarker lamps in North America, and the 2009 Cadillac Escalade Platinum uses LEDs for the low and high beams, as well as for the position and sidemarker lamps.

The commercial vehicle industry has rapidly adopted LEDs for virtually all signaling and marking functions on trucks and buses, because in addition to the fast rise time and concomitant safety benefit, LEDs" extremely long service life reduces vehicle downtime. Almost all commercial vehicles use exterior lighting devices of standardised format and fitment, which has cost-reduced and sped the changeover.

[edit] Variable-intensity signal lamps

Internationalized ECE regulations explicitly permit vehicle signal lamps with intensity automatically increased during bright daylight hours when sunlight reduces the effectiveness of the brake lamps, and automatically decreased during hours of darkness when glare could be a concern. Both US and ECE regulations contain provisions for determining the minimum and maximum acceptable intensity for lamps that contain more than a single light source.