Lighting Service

LightingThe main purpose of lights on a vehicle is to enable the driver to see and for otherroad users to be able to see the vehicle after dark and in other conditions of poor

visibility.

Requirements for the lights that must be fitted are:

1. Headlamps (minimum of two, one each side)

2. Side, rear, and number plate lamps

3. Direction indicator lamps (flashers)

4. Stop lamps (brake lights)

5. Rear fog lamp (at least one).

Bulbs

Two commonly used types of bulb

• Ordinary twin-filament headlamp bulb

• Quartz halogen twin-filament headlamp bulb

Ordinary twin-filament headlamp bulb

The filaments are made from tungsten wire and the glass bulb is often filled withan inert gas such as argon. This permits the filament to operate at a highertemperature and increases the reliability. One of the filaments provides the mainbeam and the other filament, which is placed a little above centre, provides thedipped beam.

Quartz halogen twin-filament headlamp bulb

Quartz halogen bulb is designed to give brighter light and

to prevent the evaporated tungsten from being deposited

on the inside of the bulb.

some common bulbsFestoon has a tubular shape, used fornumber-plate and interior roof lighting.Miniature centre contact (MCC) 1-5 watthas a bayonet cap consisting of two locating pins projecting from eitherside of the cylindrical cap. Cap 9mm diam. It has a singlecentral contact (SCC), with the metal cap body forming the second contactsCapless bulb have a semi-tubular glass envelope with a fl attened end, whichprovides the support for the terminal wires , used for panellights, sidelights and parking - They are now very popular due to the low cost

Single contact, small bayonet cap (SBC) Cap dia. 15mm . The small 5 W bulb, is used for side or tail lights and the larger 21 W bulb is used for indicators, hazard, reversing and rear fog-lights.

Double contact, small bayonet capIt has two fi laments, one end of each being connected to anend contact, and both of the other ends are joined to the cap body forming a third contact, which is usually the earth. used for the stop light and the other for the tail light. They are rated at 21 and 5 W (21/5 W) respectively.

External LightsSidelights

• A vehicle must have two sidelights each with wattage of less than 7 W.

• Most vehicles have the sidelights incorporated as part of the headlight assembly

Rear lights

• Not less than 5 W. Their position must be within 400 mm from the vehicle edge and over 500 mm apart, and between 350 and 1500 mm above the ground.

Brake lights

• There two lights are often combined with the rear lights. They must be between

• 15 and 36 W each, with diffused light and must operate when any form of first

line brake is applied.

Reversing lights

No more than two lights may be fitted with a maximum wattage each of 24 W.

The light must not dazzle and either be switched automatically from the gearbox

or with a switch incorporating a warning light. Safety reversing ‘beepers’ are now

often fitted in conjunction with this circuit, particularly on larger vehicles.

External LightsDay running lights

• These lights come on with the ignition and must only work in conjunction with the rear lights. Their function is to indicate that the vehicle is moving or about to move. They switch off when parking or headlights are selected.

Rear fog lights

• One or two may be fitted but, if only one, then it must be on the offside or centre line of the vehicle.

Front spot

• If front spot lights are fitted (auxiliary driving lights). If the lights are non-dipping then they must only operate when the headlights are on main beam.

• Spot lamps are designed to produce a long beam of light to illuminate the road in the distance.

• Front fog lamps may only be used in fog or falling snow.

• They are designed to produce a sharp cut off line such as to illuminate the road just in

front of the vehicle but without reflecting back or causing glare.

Headlight Reflector The object of the headlight reflector is to direct the random light rays produced by the bulb into a beam of concentrated light by applying the laws of reflection

Headlight Levelling The principle of headlight levelling is very simple, in that the position of the lights must change depending on the load in the vehicle.

Manual headlight levellingAutomatic headlight levelling

Repair and maintenanceSome service and repair operations may require components and cables to be disconnected. In such cases, the procedures fortaking connectors apart should be observed and care taken to avoid damage to the pins. Damage to pins may cause theconnection to develop a high resistance or to fail completely. Should it be necessary to probe connections, in an endeavour totrace a fault, every effort should be made to prevent damage to waterproofing and electrical insulation.

Circuit protection - fusesThe purpose of the fuse is to provide a ‘weak’ linkin the circuit that will fail (blow) if the currentexceeds a certain value and, in so doing, protectthe circuit elements and the vehicle from thedamage that could result from excess current.The fuse is probably the best known circuitprotection device.Fuses have different current ratings and thisaccounts for the range of types available. Caremust be taken to select a correct replacement andlarger rated fuses must never be used in anattempt to ‘get round’ a problem. Many modernvehicles are equipped with a ‘fusible link’ that isfitted in the main battery lead as an added safetyprecaution. It is common practice to place fuses together

in accessible place on the vehicle. Another feature of theincreased use of electrical/electronic circuits on vehicles isan increase in the number of fuses to be found on a vehicle

Types of fuses

Headlight Beam SettingTo set the headlights of a car using an aiming board the following procedure should be adopted.1. Park the car on level ground square on to a vertical aiming board at a distance of 10 m if possible. The car should be unladen except for the driver.2. Mark out the aiming board as shown below.3. Bounce the suspension to ensure it is level.4. With the lights set on dip beam, adjust the cut-off line to the horizontal mark, which will in most cases be 1 cm below the height of the headlight centre for every 1 m the car is away from the board.* The break-off point should be adjusted to the centre line of each light in turn.

Gas discharge headlamps (GDL) GDL are now being fitted to vehicles. They have the potential

to provide more effective illumination and new designpossibilities for the front of a vehicle.The new headlamps make a significant contribution towardsimproving aerodynamic styling and suitable lighting positionsbecause they can be relatively small.The GDL system (also known as high intensity discharge or HID)consists of three main components.

LampThis operates in a very different way from conventionalincandescent bulbs. A much higher voltage is needed.

Ballast systemThis contains an ignition and control unit and converts theelectrical system voltage into the operating voltage required bythe lamp. It controls the ignition stage and run up as well asregulating during continuous use and finally monitorsoperation as a safety aspect.

the operating principle of a GD bulb

Ballast system to control a GDL

HeadlampThe design of the headlamp is broadly similar to conventional units. To meet the limits set for dazzle, a more accurate finish is needed, hence more production costs are involved.The source of light in the gas discharge lamp is an electric arc, and the actual discharge bulb is only about 10 mm across. Two electrodes extend into the bulb, which is made from quartz glass. The gap between these electrodes is 4 mm.The distance between the end of the electrode and the bulb contact surface is 25 mm - this corresponds to the dimensions of the standardized H1 bulb.At room temperature, the bulb contains a mixture of mercury, various metal salts and xenon under pressure. When the light is switched on, the xenon illuminates at once and evaporates the mercury and metal salts.The high luminous efficiency is due to the metal vapour

mixture. The mercury generates most of the light and the metal salts affect the colour spectrum.

The spectrum of light produced by the GDL compared with that from a halogen H1bulb.

The difference in output between the D1 and H1 bulbs

The following four stages are run through in sequence to start the D1 (GDL) lamp, .• Ignition - a high voltage pulse causes a spark to jump between the electrodes, which ionizes the gap. This creates a tubular discharge path.• Immediate light - the current flowing along the discharge path excites thexenon, which then emits light at about 20% of its continuous value.• Run-up - the lamp is now operated at increased wattage, the temperature rises rapidly and the mercury and metal salts evaporate. The pressure in the lamp increases as the luminous flux increases and the light shifts from the blue to the white range.• Continuous - the lamp is now operated at a stabilized power rating of 35 W.If the GDL system is used as a dip beam, the self-levelling lights are required because of the high luminous intensities.

The xenon bulb is a micro-discharge bulb filled with a mixture of noble gases including xenon. • The bulb has no filament, as is the case with a

halogen bulb, but the light arc is createdbetween two electrodes.

• As is the case with other gas discharge bulbs,the xenon bulb has an electronic starter forquick ignition, and requires an electronicballast to function properly.

• The xenon bulb provides more than twice theamount of light of a halogen bulb, while onlyconsuming half the power, So the driver cansee more clearly, and the car has more powerfor other functions.

• it is environmentally friendly.• The clear white light produced by the xenon

bulb is similar to daylight.• The bulb need only be replaced in exceptional

cases.

The xenon bulb

The light produced by a xenon bulb is, in fact, not bluebut white, falling well within the internationalspecifications for white light – the light only appearsblue in comparison to the warmer ‘yellow’ lightproduced by halogen. However, it clearly appearswhite in comparison to daylight. Technically speaking,it is possible to adapt the light colour produced, butthis would lead to a substantial loss of intensity,thereby cancelling out the particular advantages.

The xenon lighting

The xenon bulb

Ultraviolet (UV) headlightsThe GDL can be used to produce ultraviolet (UV) lights. Since UV radiation is virtually invisible it will not dazzle oncoming traffic but will illuminate fluorescent objects such as specially treated road markings and clothing. . The UV light will also penetrate fog and mist, as the light reflected by water droplets is invisible.It will even pass through a few centimeters of snow.Cars with UV lights use a four-headlamp system. This consists of two conventional halogen main/dip lights and two UV lights. The UV lights come on at the same time as the dipped beams, effectively doubling their range but without dazzling.Two-stage blue filters are used to eliminate visible light. Precise control of the filter colour is needed to ensure UVB and UVC are filtered out, as these can cause eye damage and skin cancer. This leaves UVA, which is just beyond the visible spectrum and is used, for example, in suntan lamps. However, some danger still exists; for example, if a child were to look directly and at close range into the faint blue glow of the lights. To prevent this, the lights will only operate when the vehicle is moving.

Light emitting diode (LED)Most of the major manufacturers now use of LEDs for some lighting applications.

LEDs quickly found applications in the interior of the vehicle,particularly in dashboard displays. However, until recently, legislation has prevented the use of LEDs for exterior lighting.The advantages of LED lighting are1. clear, 2. the greatest being reliability, 3. they turn on quicker than ordinary bulbs,4. LED have a typical rated life of over 50 000 hours,

compared with just a few thousand for incandescent lamps.

5. ‘turn-on’ time is important; the times are about 130 ms for the LEDs, and 200 ms for bulbs

6. Heavy vehicle side marker lights are an area of use where LEDs have proved popular

Disadvantages LEDs are more expensive than bulbs

Infrared LightsInfrared thermal-imaging systems are going to be fitted to cars. The Cadillac division of General Motors has a system called ‘Night Vision’ as an option. After ‘Night Vision’ is switched on, ‘hot’ objects, including animals and people show up as white in the thermal image, Every object at a temperature above absolute zero (–273.15 °C) emits some kind of infrared radiation.On the vehicle system a camera unit sits on headlamp-type mountings in the centre of the car, behind the front grille. Its aim is adjusted just like that of headlamps. The mid-grille position was chosen because most frontcollisions involve offset rather than full head-onimpacts. However, the sensor is claimed to be toughenough to withstand 9 mph (14.5 kph) bumper impactsanyway. The sensor is focused 125 m ahead of the car.The outer lens of the sensor is coated with silicon toprotect it against scratching. Behind this two lenses aremade of black glass called tecalgenite. This is acomposite material that transmits infrared easily butvisible light will not pass through it.

Night vision system in use

Other lighting technologymono-colour technology

With this technology, in addition to the traditional redfunctions (stop, tail lamp and fog), the reverse and turnsignal functions appear red when not in use, but emitwhite and yellow light respectively when functioning.Several technologies make this possible.

Bending Light This system consists of a bi-xenon projector, or reflectorheadlamp, that can rotate up from its normal position.An additional projector, reflector, or a combination ofthe two can be used to deliver more light into a roadbend. The actuation of the motorized lighting unit,within each headlamp assembly, is controlled by anelectronic control unit, which employs signals from thesteering wheel and wheel-speed sensors. A link to asatellite navigation system (GPS) can also be used ifrequired.

Dynamic bending light and normal lighting

Bending Light includes three distinct lighting types:• Motorway Lighting – typically above 80 km/h (50 mph), the low-beam function of the head-lamp is raised using a signal received from the wheel-speed sensor to actuate a self-levelling system, which increases driver visibility at high speeds.• Adverse Weather Lighting – provides, under reduced-visibility conditions in fog, rain and snow, additional illumination to help keep track of road edges, while light is removed from the foreground to reduce reflection from the wet road.• Town Lighting – in well-illuminated urban areas the light beam is lowered and lateral light is increased, improving pedestrian and cyclist identif cation at crossings as well as reducing dazzle.

Bending Light is an intelligent headlamp system that optimizes the night-time illumination of road curves by directional control of vehicle headlamps. To turn an increased quantity of light into road bends automatically, Bending Lightsystems adopt several flexible design approaches. Dynamic Bending Light (DBL) uses a Bi-Xenon lamp (projector or reflector type) housed in each headlamp unit, together with an electronic actuator and an electronic control unit.This design facilitates the horizontal rotation of the Bi-Xenon lamp by up to 15° from the normal ‘straight-ahead’ position). This function is controlled by a microcontroller linked to the vehicle’s data network with real time inputs from both the steering angle and speed sensors. Fixed Bending Light (FBL) employs an additional projector or reflector type lamp integrated into theheadlamp unit at a 45° angle.

Intelligent lighting

Single light source lightingIt is possible to use a gas discharge lamp (GDL)as a central source for vehicle lighting.Development of this new headlamp systemallows a reduction in headlamp dimensions forthe same output or improved lighting with thesame dimensions. The principle is that lightfrom the ‘super light source’, is distributed tothe headlamps and other lamps by a light-guideor fibre-optic link. The light from the GDLenters the fibre-optics via special lenses andleaves the light-guide in a similar manner.A patterned covered lens provides the requiredlight distribution. Shields can provide functionssuch as indicators, or electro-chromaticswitches may even become available.

GDL as central light source for all the vehicle lights

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