Why Headlights Dim With Time

15 December 2015
 Categories: , Blog


You need bright headlights to see the road and for other road users to see you. Thus, dim headlights that reduce your visibility is a dangerous situation you should promptly solve. Here are some of the common causes of such dimness:


Many cars have headlight lenses made from plastic. When ultraviolet (UV) radiation from the sun reacts with the plastic, it accelerates its reaction with oxygen in the air; this is the process of oxidation. The transparency of the oxidized material reduces. Fortunately, oxidation only happens on the outermost surface of the lens, so thorough cleaning (with appropriate chemicals) restores such headlights.

Dents and Pits on the Head

Apart from oxidation, road damage may also reduce your headlights' brightness. Bits of road debris, such as small rocks and sand, continually hit your car (including its headlights) whenever you are on the road. The physical force of the particles on the headlights causes small dents and pits on its surface. Such imperfections diffuse light rays from the bulb, which reduce your visibility. The more you drive, the more these damages occur. Driving over rough roads with lots of debris also accelerates the process.

Sanding the surfaces of the headlights, using appropriate restorative kits, may get rid of these imperfections. It needs to be done carefully, preferably by an experienced person, to prevent further damage.

Water Vapor

The accumulation of water vapor within the headlights may also lead to reduced visibility. The moisture scatters the light making it appear diffused on the road. A typical headlight has air and water vapor trapped in the lamp assembly. When the temperature falls, and the headlight cools, the vapor condenses into moisture, and the diffusion commences.

Things should normalize when the temperature rises again, but this doesn't always happen. For example, the headlights' temperature may not rise if you constantly park your car in the shade. The same thing may happen if your headlight assembly isn't properly vented, such as if the vents are plugged with debris.

Dirt Accumulation

Lastly, your reduced visibility may be due to nothing more than dirty headlights. Dirt and chemicals on the road or from your car (such as oil and tar) may form a film on the surfaces of the headlights. Since such layers are opaque, they reduce the amount of light from the bulb hitting the road. This may be the case if you regularly drive over dusty roads but only give your car a light washing.

If your headlights are still dim after dealing with the above issues, then you are dealing with a more serious problem. For example, an electrical fault may be interfering with the flow of current to the bulbs. Take your car to a mechanic, like Bonita Point Auto Care 76, for professional diagnosis.