Wikicars, a place to share your automotive knowledge


Jump to: navigation, search

The 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 by which 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 intended travel, and brake status.

Forward illumination

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

Dipped (low, passing, meeting)-beam headlamps

Main article: Headlamp
E-code dipped/low beam

Dipped-beam (low-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 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.

Main (high, driving)-beam headlamps

Main article: Headlamp
European E-code high/full beam

Main-beam (high-beam, driving-beam) headlamps provide a bright, centre-weighted distribution of light with no especial control of light directed towards other road users' eyes. As such, they are only suitable for use when alone on the road, as they will dazzle other drivers. International ECE Regulations permit higher-intensity high-beam headlamps than are allowed under North American regulations.

Driving lamps

High/full beam augmented by auxiliary lights

"Driving lamp" is an obsolete term most often used to refer to auxiliary high-beam headlamps. 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.

Front fog lamps

Fog lamps provide a wide, bar-shaped beam of light with a sharp cutoff at the top, and are generally aimed and mounted low. 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 use without headlamps may not be permitted in some countries ).

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.

The respective purposes of front fog lamps and driving lamps are often confused, due in part to persistent misapprehension by the public at large 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 necessitating their use are very rare, and there is no legal requirement for them, so their primary purpose is frequently cosmetic. Studies have shown more people inappropriately use their fog lamps in dry weather than use them properly in poor weather in North America.

Cornering lamps

On some models in North America, front white "cornering lamps" provide extra lateral illumination in the direction of an intended turn. These are actuated in conjunction with the turn signals, though they burn steadily. These have traditionally been prohibited under international UN/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.


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; "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 sidemarker lights described below. These lamps may emit white or amber light in North America; elsewhere in the world they must emit white light only. 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. Today, it is 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 as an attempt to optimize the level of light used at night in built-up areas.

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 candela.

In Germany, the StVZO (Road Code) requires 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 (amber or white) 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 those driving past. This function is served passively and without power consumption in North America by the mandatory sidemarker retroreflectors.

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 or daytime 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 percent and 20 percent of normal low-beam intensity. UK DRLs must emit at least 200 candela straight ahead, and no more than 800 candela in any direction. In practise, most vehicles were equipped with the dim-dip option, rather than DRLs.

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 parking lamps (commonly used by British drivers in city traffic after dark) and dipped/low beams, because 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 use such dim-dip systems.

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.

Rear position lamps (tail lamps)

Nighttime vehicle conspicuity to the rear is provided by red rear taillamps (properly: "rear position lamps") and red rear-facing retroreflectors.

Rear registration plate lamp

The rear registration plate must be illuminated by a white lamp whenever the position lamps are active.

Sidemarker lights and retroreflectors

In North America, amber front and red rear sidemarker lamps and retroreflectors 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 with the turn signals.

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 caused automakers to change the rear sidemarker colour from red to amber on their models so equipped in the Japanese market.

Daytime running lamps

Main article: Daytime running lamp

Daytime conspicuity may be provided by daytime running lamps (DRL). These may either be separate lamps, or the function may be provided by other 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 alternatively permit low-beam headlamps to be used as daytime running lamps. Hungary, Canada, Sweden, Norway, Slovenia, Austria, Finland 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.

Rear fog lamps

(ECE Regulation 38, SAE J1319) In Europe, vehicles must be equipped with one or two bright red "rear fog lamps" (or "fog taillamps"), which are switched on manually 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 rear fog lamps are not required equipment in the U.S.

Most jurisdictions permit rear fog lamps to be installed either singly or in pairs. 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 Regulations require a separation of at least 10 cm between adjacent illuminated edges of brake lamps and rear fog lamps.


Turn signals

Turn signals (properly "directional indicators" or "directional signals", also "indicators," "directionals," "blinkers," or "flashers") are signal lights mounted near the left and right front and rear corners, and sometimes on the sides of vehicles, used to indicate to other drivers that the operator intends a lateral change of position (turn or lanechange). Electric turn signal lights were devised as early as 1907 (US patent 912,831), but were not widely offered by major automobile manufacturers until after 1939. 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).

Today, turn signals are required on all vehicles that are driven on public roadways in most countries. They 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 flash in phase with one another; North American regulations permit sidemarkers wired for side turn signal functionality to flash in opposite-phase. Worldwide regulations stipulate an 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.

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. Recently, some automakers have begun incorporating side turn signal devices into the sideview mirror housings, rather than mounting them on the vehicle's fenders. There is some evidence to suggest these mirror-mounted turn signals may be more effective than fender-mounted items.

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

Until the early 1960s, most front turn signals worldwide produced white light and most rear signals produced 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. Presently, 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, and US 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. US regulators and other proponents of red rear turn signals claim there is no proven lifesaving benefit to amber signals.

Sequential turn signals

Sequential signal retrofitted to a Pontiac Fiero.

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 in 1970 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.

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

While U.S. Federal and Canadian motor vehicle safety standards prohibit sequential turn signals on vehicles built after 1 January 1970, Federal standards do not apply to vehicles in use, and so extension of this regulation to vehicles in use is left as a matter of choice for each state or province.

Stop lamps

Red-colored steady-burning rear lights, brighter than the taillamps, 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 candela. In North America, the acceptable range for a single-bulb brake lamp is 80 to 300 candela.

Center High Mount Stop Lamp (CHMSL)

In North America since 1986, in Australia 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 stop lamps on vehicles are traditionally placed in the same housing as the tail lights and turn signals. The CHMSL, which must burn steadily and is not permitted to flash, provides advance warning to vehicle operators whose view of the braking vehicle's regular stop lamps is blocked by interceding vehicles. The CHMSL also helps to disambiguate brake vs. turn signal messages, particularly in North America, where red rear turn signals identical in appearance to brake lamps are permitted.


On passenger cars, the CHMSL may be placed above the backglass, affixed to the vehicle's interior just inside the backglass, or it may be integrated into a spoiler. Trucks, vans and commercial vehicles usually have the CHMSL mounted to the trailing edge of the vehicle's roof. The CHMSL must in all cases be laterally centred on the vehicle, and its height is regulated in absolute terms as well as with respect to the mounting height of the vehicle's conventional (left and right) brake lamps.


The 1968–1971 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. The Oldsmobile Toronado from 1971 had dual high-mounted supplemental brake lights as standard. 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%.<ref>Template:Citation/core{{#if:|}} </ref> It is possible that today, familiarity with the third stop lamp has reached the extent that drivers may not respond quickly enough if a vehicle without a functioning CHMSL decelerates in front of them, since the familiar cue is absent.

In 1986, the United States National Highway Traffic Safety Administration and Transport Canada mandated that all new passenger cars have a CHMSL installed. Because Elizabeth Dole was Secretary of Transportation at the time, these lights were occasionally referred to as Dole lights. 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.

Emergency Braking Display

Mercedes-Benz 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, while 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 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 vs. Mercedes differ not only in operational mode (flashing vs. growing), but also in such parameters as deceleration threshhold 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 (in Europe, all vehicles must have amber rear turn signals separate from the brake lamps, and flashing-red was not assigned any meaning until the development of emergency-braking warning systems.)

Reversing lamps

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 UN/ECE regulations. However, in the past, some countries have permitted amber reversing lamps. A notable example is Australia, which permitted amber reversing lamps until the early 1980s. Vehicle manufacturers, faced with the task of localizing American cars originally equipped with combination red brake/turn signal lamps and white reversing lamps, 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 to add additional lighting devices to the rear of the vehicles.

Construction & Technology

Light sources

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 watt, 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. Some recent-model vehicles use small tungsten-halogen light bulbs.

Light Emitting Diodes (LED)

LEDs are being used with increasing frequency in automotive signalling lamps. They operate with much lower power consumption, have longer service lives, are nearly impervious to vibration damage, and 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 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 Center High Mount Brake 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 commercial vehicle industry has rapidly adopted LEDs for virtually all signalling and marking functions on trucks and buses, because in addition to the fast rise time and concommitant safety benefit, LEDs' extremely long service life reduces vehicle downtime.

Neon tubes

Neon lamp tubes have been used as CHMSLs on such vehicles as the late-1990s Ford Explorer, and have been exhibited as features on concept cars 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 popularity as automotive signalling device light sources.

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.

See also

External links