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. Contents [hide] * 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 # 3.2.2.1 Side turn signals # 3.2.2.2 Electrical connection and switching # 3.2.2.3 Turn signal colour * 3.2.2.3.1 Colour durability # 3.2.2.4 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) # 3.3.4.1 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. Trafficator. 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'Éclairage, 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 illuminated—including 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 candela