Demonstrate automobile bulbs and lights.

Demonstrate automobile bulbs and lights.

BULBS

Joseph Swan in the UK demonstrated the first light bulb in 1878. Much incremental development has taken place since that time. The number, shape and size of bulbs used on vehicles is increasing all the time. Figure shows a common selection. Most bulbs for vehicle lighting are generally either conventional tungsten filament bulbs or tungsten halogen.

In the conventional bulb the tungsten filament is heated to incandescence by an electric current. In a vacuum the temperature is about 2300 ° C. Tungsten is a heavy metallic element and has the symbol W; its atomic number is 74; and its atomic weight 2.85. The pure metal is steel grey to tin white in color. Its physical properties include the highest melting point of all metals: 3410 ° C.

Pure tungsten is easily forged, spun, drawn and extruded, whereas in an impure state it is brittle and can be fabricated only with difficulty. Tungsten oxidizes in air, especially at higher temperatures, but it is resistant to corrosion and is only slightly attacked by most mineral acids. Tungsten or its alloys are therefore ideal for use as filaments for ele ctric light bulbs. The filament is normally wound into a ‘spiraled spiral’ to allow a suitable length of thin wire in a small space and to provide some mechanical strength.

LIGHTS

Basic lighting circuit: -

Figure shows a simple lighting circuit. Whilst this representation helps to demonstrate the way in which a lighting circuit operates, it is not now used in this simple form. The circuit does, however, help to show in a simple way how various lights in and around the vehicle operate with respect to each other. For example, fog lights can be wired to work only when the sidelights are on. Another example is how the headlights cannot be operated without the sidelights first being switched on.

External lights: -

Regulations exist relating to external lights, the following is a simplified interpretation and amalgamation of current regulations; the range of permissible luminous intensity is given in brackets after each sub heading.

Sidelights (up to 60 cd): -

A vehicle must have two sidelights each with wattage of less than 7W. Most vehicles have the sidelights incorporated as part of the headlight assembly.

Rear lights (up to 60 cd): -

Again, two must be fitted each with wattage not less than 5W. Lights used in Europe must be ‘E’ marked and show a diffused light. Their position must be within 400 mm from the vehicle edge and over 500 mm apart, and between 350 and 1500mm above the ground.

Brake lights (40–100 cd): -

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. Brake lights must be between 350 and 1500 mm above the ground and at least 500 mm apart in a symmetrical position. High-level brake lights are now allowed and, if fitted, must operate with the primary brake lights.

Reversing lights (300–600 cd): -

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

Day running lights (800 cd max): -

Volvo use day running lights as these are in fact required in Sweden and Finland. 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.