Why do the headlights of two wheelers burn brightly.jpg

The head lights of both the two wheeler and the four wheeler vehicles are powered by electricity. These are incandescent lamps where an electric current heats a filament to bright incandescence; more the current brighter the lamp glows. In turn, more current results from higher potential difference or voltage when applied across the electrical resistance of the filament.  

In both the two and four wheelers, electricity is generated by a dynamo, often called the magneto or alternator of the vehicle. The generator produces an alternating voltage and is used for all the electrical needs of the vehicle, such as running the fuel pump and the starter motor, ignition in the petrol engines and operation of other electrical accessories such as the fuel feeding and speed regulation electronics, air conditioner, music system, lights and indicators etc.

In most of the two wheelers without auto starter facility, the initial fuel feeding is accomplished by kick start mechanism causing the engine suction and the ignition is initiated by the voltage generated by the magneto. The engine running is sustained subsequently by the repetition of the same procedure during cyclic running of the engine. The head lights derive the necessary power from the generator. Therefore, when the engine is accelerated, the dynamo runs at higher speed and generates higher voltage and more power making the lights glow brighter.

However, in the four wheelers we come across these days, there is no provision for manual “kick” starting. The processes are the same as in the two wheelers. Even in the diesel vehicles, where there is no need of electrical spark for ignition, there has to be a dynamo alternator for meeting the electricity needs.

In the petrol run four wheelers, the engine ignition has to be through the spark plugs and excited by electricity, anyway. Therefore, the four wheelers, of both petrol and diesel variety, are fitted with a powerful battery which is used for starting the vehicle and the engine is taken over by the alternator during the regular running. Further, the battery is charged by the alternator during the running period of the vehicle. Thus, the battery is chosen to be of fairly high capacity. This battery supplies power to the head lights even when the engine is not started or kept at low acceleration. The power regulator circuit controls the power supply so that there is no variation of brightness of the head lights during the change of accelerator operation.