The most basic vehicle conspicuity devices are retroreflectors (also reflex reflectors or, archaically, cat's eyes), which despite emitting no light on their own, are regulated as automotive lighting devices. These devices reflect light from other vehicles' headlamps back towards the light source, that is, other vehicles' drivers. 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 amber front and red rear side-facing retroreflectors. Sweden, South Africa and other countries have at various times required white front-facing retroreflectors.
[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, 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. The front position 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. 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.
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) 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 (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 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] 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[20] 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 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 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 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.[21]
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.
Extensively redundant rear lighting installation on a tour bus
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Extensively redundant rear lighting installation on a tour bus
[edit] Rear position lamps (tail lamps)
Nighttime vehicle conspicuity to the rear is provided by rear position lamps (North American terms: taillamp, taillight, tail lamp, tail light; UK term rear light). These are required to produce only red light, and to be wired such that they are lit whenever the front position lamps are illuminated—including when the headlamps are on. Rear position lamps may be combined with the vehicles 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. 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.
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] Rear registration plate lamp
The rear registration plate must be illuminated by a white lamp whenever the position lamps are active.
[edit] Sidemarker lights
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.[22] 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.[23]
[edit] Daytime running lamps
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 candela on axis and no more than 800 candela in any direction. Most countries applying ECE Regulations 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 candela, and can be implemented as high-beam headlamps running at less-than-rated voltage. This has provoked a large number of complaints about glare.[24][25]
[edit] 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.
[edit] Signalling devices
[edit] Turn signals
Vehicle with its left directional signal activated. Front and side turn signals are visibly illuminated.
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Vehicle with its left directional signal activated. Front and side turn signals are visibly illuminated.
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 (U.S. Patent 912,831), but were not widely offered by major automobile manufacturers until after 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 older cars used retractable mechanical arms for indicating rather than lights. In most implementations, they tended to be mounted to the sides just behind the front doors and swing out vertically. However, they had a tendency to be broken off very easily and did not remain popular.
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, do not dazzle those who view them, and are suitably conspicuous in conditions ranging from full darkness to full direct sunlight. Recent styling trends have raised concerns that turn signals with colourless clear lenses may pose special problems in bright sunlight.[26]
[edit] Electrical connection & Switching
Two types of dashboard turn signal telltale indicators
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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 protruding from the side of the steering column, though some vehicles have the lever mounted instead to the dashboard. In virtually all left-hand drive cars, the lever is on the left side of the column, and the driver moves the lever up to activate the right turn signal, or down to activate the left. In right-hand drive cars, the placement of the signal lever varies by maker and market. When the lever is located on the right side of the column, the lever is moved down to signal a right turn, up to signal a left. The direction in which the lever must be moved is intuitive, in that the lever must be pivoted to signal in the same direction as the steering wheel must be turned for the car to make either a left or a right turn. Virtually all vehicles have a 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.
[edit] Turn signal color
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 color 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, 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.[27][28][29][30][31]
[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. 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.[32]
[edit] Sequential turn signals
Sequential signal retrofitted to a Pontiac Fiero.
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 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.
[edit] Hazard flashers
International and North American regulations have since the 1960s 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, or an exceptionally slow-moving vehicle. 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] 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.
[edit] 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. It is often referred to as the Center Brake Light or Third Brake Light.
[edit] Rationale
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.
[edit] Placement
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.
[edit] History
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%.[33] 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.
[edit] 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 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] 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.
[edit] Construction and technology
[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 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.
[edit] 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 concomitant safety benefit, LEDs' extremely long service life reduces vehicle downtime.
[edit] 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.
[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.