How A Vehicle’s Headlights Work

The History of Headlights

When cars were first being produced, the headlight was more of a lamp, with an enclosed acetylene flame which had to be manually lit by the driver. Those early headlights were introduced in the 1880s, and gave drivers the freedom to be able to drive more safely at night. The first electric headlights were produced in Hartford Connecticut and were introduced in 1898, though they were optional on new car purchases. They had a short lifespan due to the incredible amount of energy required to produce a light bright enough to light the roadway. When Cadillac integrated a modern electrical system into automobiles in 1912, headlights became standard equipment on most vehicles. Today’s vehicles have headlights that are brighter, last longer, and have multiple facets; such as daytime running lights, the low beam, and the high beam.

Types of Headlights

There are three types of headlights. Incandescent lamps use a filament inside the glass which, when heated by electricity, produces the light. It takes a surprising amount of energy to produce such a small light; as anyone who has drained their battery by accidentally leaving their headlights on can attest to. Incandescent lamps are being replaced by more energy-efficient halogen bulbs. Halogen headlights are the most common headlights used today. Halogens replaced incandescent headlights because in an incandescent bulb, more energy is converted to heat than light, resulting in wasted energy. Halogen headlights waste far less energy. Today, some makes of cars, including Hyundai, Honda, and Audi, use High Intensity Discharge (HID) headlights.

Components of a Halogen or Incandescent Headlight

There are three types of headlight casing that use halogen or incandescent bulbs.

  • The first, the lens optics headlight, is designed so that the filament in the light bulb is placed at or near the focus of a reflector. In these, prism optics molded in the lens refract the light, which spreads it upward and forward to provide the light desired.

  • The reflector optics headlight also has the filament in the light bulb at the base of the light, but uses multiple mirrors to achieve the light being spread properly. In these headlights, the lens is merely used as a protective cover for the light bulb and mirrors.

  • Projector lamps are like the other two types but also may have a solenoid which when activated, will pivot to provide the low beam. In these headlights the filament is located as an image plane between a lens and reflector.

Components of an HID Headlight

In these headlights, a mixture of rare metals ands gases are heated to produce a bright white glow. These headlights are about two or three times brighter than halogen headlights and can be very annoying to other drivers. They are distinguished by their bright white glow and blue tinged outline. These headlights are much more energy efficient, and have brighter output while drawing less energy. The HID headlights draw about 35 watts of power, while halogens and the old incandescents draw about 55 watts. The HID headlights are more expensive to produce though, so are mainly seen on high end vehicles.

Wear and Tear

Like any other part of the vehicle, headlights will start to lose their efficiency after a certain amount of time. HID headlights last longer than halogen lights, though both will show a distinct lack of brightness when used excessively or longer than their recommended lifespan, which is about a year for halogen bulbs and double that for HID. Some headlights in the past were a fairly easy fix for the home mechanic. He or she could simply buy the bulb from a parts store and then follow the instructions in the user manual. Newer model cars however are much more complex and can be harder to get to. In these cases, the best course of action is to use a licensed mechanic to fix your headlights.

Common Problems With Headlights

There are a few common problems with today’s headlights. They can lose brightness due to using them too long, dirty or cloudy lens covers, and sometimes a dull headlight could be a symptom of alternator problems. There could also be a cracked or broken bulb or a bad filament. A quick inspection by a licensed mechanic for a diagnosis will light the way.

How High Beams Work and When to Use Them

The difference between the low beam headlights and the high beam headlights is the distribution of the light. When the low beams are on, the light is positioned forward and down so as to light the roadway but not affect the drivers who are driving in the opposite direction. However, the high beam headlights do not have any restrictions on where the light is directed. This is why the light goes upward as well as forward; high beams are designed to give a view of the entire environment, including possible roadside hazards. With an extra one hundred feet of visibility, a high beam headlight allows a driver to see more clearly and to be safer. However, it will affect the visibility of those traveling opposite of the vehicle, and should only be used in low traffic areas.

Position of Headlights

A vehicle’s headlights should be positioned in a way so as to give the driver optimum visibility, without affecting those who are driving in the opposite direction. In older cars, the lens is adjusted with a screwdriver; in newer cars, adjustments have to be made from inside the engine bay. These adjustments allow the lenses to be tilted in various ways to create an optimum lighting condition. While not technically a headlight repair, it’s not always easy to get the correct angle and position on a headlight. A licensed mechanic has the experience to make this adjustment and ensure safer night driving.


The statements expressed above are only for informational purposes and should be independently verified. Please see our terms of service for more details

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