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A daytime running lamp (DRL, also daylight running lamp or daytime running light) is a lighting device on the front of a roadgoing motor vehicle, installed in pairs, automatically switched on when the vehicle is moving forward, and intended to increase the conspicuity of the vehicle during daylight conditions. DRLs might have been first seriously proposed in 1961 in the USA, in response to Texas then-Governor Price Daniels' drive-safely campaign.^[1].

full-voltage vs. reduced-voltage (DRL) operation of low beam headlamp on European-market Volkswagen

Scientific study of the value of DRLs has yielded widely divergent results. It is problematic and difficult to apply the successful results obtained in Scandinavian countries to jurisdictions like the U.S., Canada and Australia, as the ambient light conditions and vehicles in use are extremely different. Studies conducted in North America have thus far not shown a conclusive safety benefit to DRL and have raised questions about possible safety detriments, such as turn signal masking and glare affecting motorcycle safety, from certain DRL implementations. Nevertheless, a safety improvement is at least suggested by many studies.

Hella DRL retrofit kit offered in Sweden in the 1970s. Package text reads "Install Hella perception lights so you are seen in traffic".

DRLs were first mandated in Scandinavian countries, where ambient light levels in the winter are generally low even during the day. Sweden was the first country to require widespread DRLs in 1977. At the time, the function was known as "perception light" or "notice light". The initial regulations in these countries favored devices incorporating 21-watt signal bulbs identical to those used in brake lamps and turn signals, producing yellow or white light of approximately 400 to 600 candela on axis, mounted at the outer left and right edges of the front of the vehicle. Finland adopted a daytime-light requirement in 1972 on rural roads, and in 1982 on all roads; Norway in 1986, Iceland in 1988, and Denmark in 1990. To increase manufacturer flexibility in complying with the requirement for DRLs, the daytime illumination of low-beam headlights was added as an optional implementation. Given the ECE headlamp specifications in use in those countries, such an implementation would produce approximately 450 cd axially.

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 when the position lamps are switched on, the primary aim being to prevent drivers using only position lamps at night. UK DRLs must emit at least 200 candela straight ahead, and no more than 800 candela in any direction. These regulatory provisions were based on ILPE research and recommendations. In practice, most vehicles were equipped with the dim-dip option, rather than DRLs, and the Dim-Dip requirement was quashed by the European Commission. See Automotive lighting for more information.

European countries disagree amongst themselves as to whether DRLs should be required, permitted, or prohibited. Germany, France and others have begun to experiment with encouragements or requirements for daytime low-beam headlamp use on certain roads at certain times of year. Hungary requires hardwired daytime running lamps. ECE R48 permits but doesn't require the installation of DRLs conforming to ECE R87 on any motor vehicle type-approved as ECE-compliant, so all countries signatory to ECE R48 are required to allow vehicles so equipped to circulate in traffic. DRLs compliant with R87 emit white light of between 400 and 800 candela on axis.

Canada Motor Vehicle Safety Standard 108 requires DRLs on all new vehicles made or imported after January 1, 1990. Canada's proposed DRL regulation initially was extremely similar to regulations in place in Scandinavia, with an axial luminous intensity limit of 1,500 candela, but automakers objected, claiming it was too expensive to add a new front lighting device, and would increase warranty costs (by dint of increased bulb replacements) to run the low beams. After a pitched regulatory battle, the standard was rewritten to permit the use of reduced-voltage high beam headlamps producing up to 7,000 axial candela, as well as permitting any light color from white to amber or selective yellow. These changes to the regulation permitted automakers to implement a less-costly DRL, such as by connecting the high beam filaments in series to supply each filament with half its rated voltage, or by burning the front turn signals full time (except when actually flashing as turn indicators).

reduced-voltage high-beam DRL on a US/Canada 2002 Lexus RX300

General Motors, interested in reducing the build variations of cars for the North American market, began lobbying the DOT (United States Department of Transportation) to permit DRLs in the United States shortly after Canada required them. A prolonged regulatory battle was fought, with the DOT objecting on grounds of potential safety drawbacks and glare issues. Eventually, however, these objections were set aside and DRLs of the same types allowed in Canada (save for fog lamp DRLs) were legalized but not mandated effective with the 1995 model year. General Motors immediately equipped most (and, in following years, all) of its vehicles with DRLs beginning with the Chevrolet Corsica. Saab, Volkswagen and Subaru gradually introduced DRLs in the U.S. market beginning in 1995. In recent years, Lexus has installed high-beam or turn signal based DRLs on US models. Some Toyota models come with DRLs as standard or optional equipment, and with a driver-controllable on/off switch. Starting in the 2006 model year, Honda equipped both the Accord and new Civic with DRLs.

Public reaction to DRLs, generally neutral to positive in Canada, is decidedly mixed in the U.S. (where motorcycles have since 1976 been wired so that low beam headlamp is on whenever the engine is running—not as a matter of law, but by voluntary industry action). Thousands of complaints regarding glare from DRLs were lodged with the DOT shortly after DRLs were permitted on cars, and there was also concern that headlamp-based DRLs reduce the conspicuity of motorcycles, and that DRLs based on front turn signals introduce ambiguity into the turn signal system. In 1997, in response to these complaints and after measuring actual DRL intensity well above the 7,000 cd limit on vehicles in use, DOT proposed changes to the DRL specification that would have capped axial intensity at 1,500 candela, a level nearly identical to the European 1,200 cd and identical to the initially-proposed Canadian limit. During the open comment period, thousands of public comments were received by DOT in support of lowering the intensity (or advocating the complete elimination of DRLs from U.S. roads). Automaker sentiment generally ran along predictable lines, with European automakers experienced at complying with European DRL requirements voicing no objection to the proposal, and North American automakers vociferously repeating the same objections they raised in response to Canada's initial proposal. The DOT proposal for DRL intensity reduction was rescinded in 2004.^[2][3]

Motorcyclists have objected that DRLs on autos will reduce the conspicuity of motorcycles, and the debate has been complicated by studies showing no safety benefit to DRLs on motorcycles^[4]

DRL power consumption varies widely depending on the implementation. Current production DRL systems consume from 8 watts (dedicated LED system) to over 200 watts (headlamps and all parking, tail, and marker lights on). International regulators, primarily in Europe, are struggling to balance the potential safety benefit offered by DRL with the increased fuel consumption due to their use. Because the power to run the DRLs must be produced by the engine, which in turn requires burning additional fuel, high-power DRL systems increase CO2 emissions sufficiently to affect a country's compliance with the Kyoto protocol on greenhouse gas emissions.^[5] For that reason, low-power solutions are being encouraged ^[6] for use when and if DRLs become mandatory in ECE Regulations. LEDs and low-wattage, high-efficacy, long-life light bulbs produce appropriate amounts of light for an effective DRL without significantly increasing fuel consumption or emissions. Fuel consumption reductions of up to 0.5 mpg may be found when comparing a 55-watt DRL system to a 200-watt DRL system. ^[7] In 2006, the UK's Department of Transport also found significant reductions in emissions and fuel consumption when comparing a 42-watt DRL system to a 160-watt full headlight DRL systems. ^[8] DRL fuel consumption can be reduced to insignificant levels by the use of 8- to 20-watt DRL systems based on LEDs or high-efficacy filament bulbs.

• Automotive Lighting
• Headlamp
• Federal Motor Vehicle Safety Standard 108

• (USA) U.S. DOT Docket Viewer (Enter docket # 4124 to view U.S. DOT DRL regulation proposal and comments thereto)
• (USA) DRL fuel consumption calculations
• (Netherlands) SWOV Dutch national road safety research institute DRL fact sheet
• (Canada) Canada Motor Vehicle Safety Regulations: Daytime Running Lamps
• (USA) Association of Drivers Against Daytime Running Lights
• (Australia) Let's TURN 'EM ON - Headlights On 24/7 (Australian DRL activist website)
• (UK) UK Dim-Dip Regulatory History
• (UN) ECE Regulation 87 concerning Daytime Running Lamps
• (ES) DRL advocacy site containing list of countries with Daytime Running Lamps