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, or cornering lamps.
Headlamps
Automatic systems for activating the headlamps have been available since the mid 1960s, originally only on luxury American models such as Lincoln, Cadillac, and Imperial. Basic implementations simply turn the headlights on at dusk and off at dawn, while more advanced systems such as high-specification versions of the Twilight Sentinel also allow the driver to set a variable timer to leave the vehicle's exterior lights illuminated after exiting the vehicle to aid in finding the way in the dark.
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 dazzling other road users with excessive glare. This beam is specified for use whenever other vehicles are present ahead. UN 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. Control of glare is less strict in the North American Society of Automotive Engineers (SAE) beam standard contained in Federal Motor Vehicle Safety Standard 108 (FMVSS / CMVSS 108).
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. ECE and Japanese Regulations permit higher-intensity high-beam headlamps than are allowed under US regulations.
