Daytime running lamp

Daytime Running Lamps ("DRL", also "Daylight Running Lamps", "Daytime Running Lights") are lighting devices on the front of roadgoing motor vehicles, automatically switched on when the vehicle is moving forward, and intended to increase the conspicuity of the vehicle during daylight conditions.

Scientific study
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, for 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 disbenefits, e.g. turn signal masking, motorcycle safety reduction and/or glare, from certain DRL implementations. Nevertheless, a safety improvement is at least suggested by many studies.

Scandinavia
DRL were first mandated in Scandinavian countries, where ambient light levels are generally low even during the day. Finland was the first country to require DRL in 1972. Sweden adopted the same requirement in 1977, Norway in 1986, Iceland in 1988, and Denmark in 1990. The DRL regulations in these countries initially favored the use of 21-watt signal bulbs identical to those used in brake lamps and turn signals, mounted at the extreme outer left and right edges of the front of the vehicle, and producing approximately 400 to 600 candela on axis. To increase manufacturer flexibility in complying with the requirement for DRL, the daytime illumination of low-beam headlights was added as an optional implementation. Given the UNECE headlight specifications in use in those countries, such an implementation would produce approximately 400 cd axially. Headlamp-based DRL were required in Hungary starting in 1989. In all cases, DRLs were required to produce white light.

Canada
Canada Motor Vehicle Safety Standard 108 required DRL on all new cars made 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 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).

United States
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 DRL 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 DRL 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 DRL. Saab, Volkswagen and Subaru gradually introduced DRL in the U.S. market beginning in 1995.

Public reaction to DRL, mostly positive in Canada, was decidedly mixed in the U.S. (where motorcycles have been required since 1976 to be wired so as to burn the low beam headlamp whenever the engine is running). Thousands of complaints regarding glare from DRL were lodged with the DOT shortly after the lights were allowed, and there was also some concern that DRL 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 DRL 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.

Great Britain
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. These regulatory provisions were based on ILPE research and recommendations. In practise, 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.