How Does a Car's Headlights Work?

by Derek Odom

Basic Function

The headlights located on the front of vehicles are there to enable drivers to see at night. However, they are also used to notify other drivers of your presence in foggy conditions or a mountain pass where visibility may be very low. In the beginning, headlights were acetylene based flames which had to be manually lit by the driver. Today, we have both high and low beam functions for different driving conditions, and the headlights can be toggled on or off from inside the passenger compartment by the driver. The switch is hooked into the twelve volt power supply running through the vehicle, and when activated it sends electricity to the headlights, which in turn powers them up.


HID headlights, or High Intensity Discharge lamps, use a Xenon gas which is activated by the presence of electricity, and turns that power into usable light. These lights tend to be much brighter than the average bulb, and are more durable as well. Incandescent lamps were used in the past, but are slowly being replaced by Halogen bulbs. Incandescent bulbs use a filament inside the glass, which when heated up by the presence of electricity produces light. These types of bulbs produce great heat however, and very little relative light, meaning that energy is being wasted and therefore they are being phased out in favor of more efficient bulbs. The last popular model, the Halogen bulb, uses a similar process as the incandescent bulb, but also utilizes gas which greatly helps brighten the output. Halogen bulbs normally use iodine or bromine to react to the electric charge. These bulbs create substantially more light than the old conventional incandescent headlights, but create more heat.

Position and Aiming

The headlights on a car should be aimed so that they show the maximum amount of road in front of the vehicle, without being positioned so high that they interfere with the eyesight of drivers traveling the opposite direction. The high beam function of most headlights will provide a beam that travels upward as well as outward, and so should only be used in areas of low traffic for safety reasons. Most of the time headlights can be successfully aimed by positioning the vehicle in front of a wall or other flat surface. In older cars, they can be adjusted from the front of the lens itself by the use of set screws that are used to tilt the headlight in different directions. Most new model cars are aimed via the engine bay from the back of the bulb and need much less calibration when replacing the light.

About the Author

Derek Odom has freelanced since 2008 and is also an author of the macabre. He has been published on, and various other websites. Odom has an Associate of Arts in administration of justice.

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