Car Parts and Accessories

Auto Reflectors and Bulbs

All cars have at least two headlamps working together. Each lamp has a main beam giving maximum light ahead, and a dipped beam which is shorter and lower, so that it will not dazzle oncoming drivers, and can be used in fog.

Regulations require that the centre of the intense beam strikes the road ahead at a distance not exceeding 100 metres on a reasonably level road.

Separate filaments in one bulb provide main and dipped beams. The extra lamps that are fitted in four-headlamp systems are main beam only.

The light source is generally a tungsten filament in inert gas with halogen vapour. Older bulbs have a filament in an inert gas. The beam is shaped by a reflector and prisms in the front glass lens. With twin filaments, that of the main beam is generally located at the focus point of the reflector, to give a straight-ahead parallel beam. The dipped-beam filament is either located off-centre, or shielded so that it uses only half the reflector, to give a downward-sloping, broader beam.

Headlamp units are fitted in the car in such a way that, by screwing spring- loaded mountings in or out, the light beam can be moved for accurate setting.

Auto Aerodynamic Headlamps

Modern headlamps have become an integral part of vehicle styling. For this reason they are seldom circular. The need for shallower and wider lights was brought about by lower bonnet lines which allow improved body aerodynamics.

On older cars, headlamps which are not circular usually have a quartz-halogen or tungsten filament bulb. The styled headlamp with a quartz-halogen bulb largely replaced the sealed beam headlamp (which is usually circular). This is a one-piece glass envelope with the high and low beam filaments cemented into the back.

Since the advent of designs which use styled headlamps to assist the car’s aerodynamic shape few cars use sealed beams.

Parking lights are generally separate from the headlamp but may be in a light cluster including the turn indicator.

AutoQuartz-halogen Bulbs

When a current is applied to the filament of a quartz-halogen bulb, much higher temperatures are generated than in a tungsten filament bulb—usually about 600°C. The higher temperature makes it necessary to use a more durable casing. Quartz is most suitable for this task.

When in operation, the tungsten filament emits tungsten atoms which pass into the surrounding gas and combine with the iodine vapour to form tungsten iodide. Convection causes the tungsten iodide vapour to move to the hottest part of the bulb where a reaction occurs, separating the tungsten which returns to the filament.

This process is continuous while the filament receives current.

A quartz-halogen bulb gives a whiter, brighter light per watt of power consumed. It lasts longer and is easier to focus.

Auto Supplementing the Headlamps

Fog lamps, which are useful in fog, sea mist, low cloud and even snow, can be fitted as accessories.

Fog lamps are designed to produce a wide beam with a sharp cut-off at the top. This enables the driver to see better the nearside kerb and any reflective markings along the centre or left-hand edge of the road. It also helps the driver keep a sense of direction, as it is easy to become disorientated in fog if only one part of the road can be seen.

No fog light may be mounted more than 600 mm above ground level (measured to the centre of the lamp) and the intense part of each beam may not strike the road more than 45 metres ahead. They must not cause glare to oncoming traffic or be deflected towards the right.

The left-hand fog lamp should be mounted so that it accentuates the left-hand side of the road for extra safety.

Some fog lamps produce a yellow-tinted light which can help reduce glare. This colouring is a matter of driver preference, and unless a sealed-beam unit has already been fitted, it may be possible to fit a yellow bulb, or change the lens if a white light is required.

There is no basis for the belief that a yellow beam provides the driver with better visibility than a white one—except possibly in light mist or drizzling rain.

High-intensity lamps, usually fitted in pairs, which provide illumination for up to twice the distance of conventional lamps, may not be used in South Africa. Beam widths vary, but are usually narrow and concentrated for maximum range.

Spot, flood or handlamps may only be used on official vehicles, such as ambulances, although doctors are allowed to use spotlights on their cars.

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