Introduction

What is automotive lighting system?

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.

Colour of light emitted

The colour of light emitted by vehicle lights is largely standardised by longstanding convention, first codified in the 1949 Vienna Convention on Road Traffic and later specified in the 1968 United Nations Convention on Road Traffic 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.
 

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.

 

Headlamps

A headlamp is a lamp, usually attached to the front of a vehicle such as a car, with the purpose of illuminating the road ahead during periods of low visibility, such as night or precipitation. While it is common for the term headlight to be used interchangeably in informal discussion, headlamp is the technically correct term for the device itself, while headlight properly refers to the beam of light produced and distributed by the device.

A headlamp can also be mounted on a bicycle (with a battery or small electrical generator), and most other vehicles from airplanes to trains tend to have headlamps of their own.

Low 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. Control of glare is less strict in the North American SAE beam standard contained in FMVSS / CMVSS 108.

Main 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.

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. The "driving beam" term has been supplanted in North American regulations by the functionally descriptive term auxiliary high-beam lamp. 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.

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. 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 glare back 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.
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.

Corner lamps

On some models, white corner 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 as well as for rear cornering lamps. 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).

Front position 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 side marker 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.

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.

Tail lamps

Night time vehicle conspicuity to the rear is provided by rear position lamps (also called tail lamps 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.