How Do a Car's Headlights Work?

Updated April 17, 2017

A car's headlights are operated and controlled manually from inside the car itself. A headlight switch, which is normally located on the dashboard or turn signal switch, relays an electrical signal from the car battery directly to the headlights themselves. When the headlight switch is activated, an electrical connection is opened and electricity flows freely form the car battery to the headlights.

Headlight Bulb and Housing

Each individual car headlight is set inside a headlight housing, which is normally anchored to the grill of a car. A car headlight, which is basically a giant light bulb, is normally covered with a special type of glass and/or plastic that further illuminates the brightness of each light. Most car headlights are halogen headlights, which are high-powered headlights with special antiglare properties.

Headlight Settings

Car headlights can be operated at different power outputs. Most car headlights come with three basic power levels: regular beams, high beams and low beams (parking beams). Each individual power level operates within the same headlight. However, the high-beam setting, which is the most powerful, operates via a special set of bulbs located within the main headlight unit. The remaining headlight power options use the same set of bulbs.

Headlight Adjustments

For a car's headlights to operate correctly, it is imperative that they be positioned to illuminate as much of the roadway in front of a car as possible. All headlights have adjustment screws on the headlight housings. These adjustment settings allow the position of the headlights--their angle as well as the angle of the light beams--to be adjusted.

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