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8 Reasons Why Your Headlights Are Dim

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Headlights are essential parts of your car as they help you see your path and the obstacles around you, especially at night and in foggy or misty conditions. They also make other road users aware of your presence. Driving without headlights is one of the most dangerous things a driver can do.

Dim headlights are near as dangerous as driving with no lights. These lights do not give you adequate coverage to see your way sufficiently, making it dangerous to drive around. Discover the common reasons that can cause you dim lights here and the solutions you can take to restore your lights to full power.

Reasons Why Your Headlights Are Dim

Oxidized Lenses

Modern headlights have a transparent plastic casing that protects the bulbs from exposure. Over time, though, the plastic lenses discolor because of constant exposure to sunlight, leading to oxidation. 

A buildup of oxidation on a car headlight

This discoloration causes the light from the bulbs to get obscured, leading to poor vision. These plastic casings also get scratched by objects like pebbles, branches, and other debris. You can give the lenses a new lease of life by having your auto shop remove this coating that has formed on them. 

A specialist removing oxidation from a car headlight

Because that coating also occurs due to age, the coating removal only serves as a momentary fix. You can also purchase a coat removal DIY kit and do it yourself from home if you love such projects.

Aging Bulbs

Bulbs that have lived out their life will start to fade. Halogen bulbs tend to have this weakness as they age since the gas inside creates a film inside the bulb and prevents the light from the filament from making its way out. You will find such bulbs dimmer and dimmer as the days go by. 

A pair of Xenon HID bulbs

Xenon HID and LED bulbs also grow dim as they age. At times poor components can have them growing dim before their time. In such cases, the only solution is to replace the bulbs with new ones. To defeat premature aging, always ensure you replace your lighting with good quality bulbs from trusted brands.

You can diagnose aging bulbs by checking how bright they are when the car is packed. You can tell whether the headlights are both giving the same brightness or one of them is emitting less light than usual. 

A specialist replacing a Xenon bulb.

You can easily replace the bulbs if you have confidence in DIY projects. You only need to know which bulbs were assembled as stock and get the same. You can also do some research and upgrade your bulbs to better-performing ones as long as they fit the housing you have and have the proper holders.

Corroded Wiring

The wiring can sometimes get corroded when electricity encounters resistance and pushes through. This corrosion can damage connecting points, sometimes preventing proper flow and delivery of electricity to the bulbs and other components. 

An electrician working on car wiring.

You can restore corroded connectors by sanding or brushing them with a wire brush to help them deliver the amount of electricity required. Damaged connectors need complete replacement with new connectors.

You also need to check the wires are not damaged or broken at any point. This damage can disrupt the electricity flow making the bulbs have flickering or dim light. An electrician can assess these wires for you for any damage. 

Malfunctioning Alternator

The alternator provides electricity to the headlights and other parts that need electricity to run, like power windows, steering, and windshield wipers. A malfunctioning alternator will not deliver enough power to the headlights, and you will notice them dimming. 

A close-up of a car alternator

The dimming related to the alternator happens right after switching the car on. The headlights tend to be bright right at the point of the car coming on as they are getting their electric current from the battery. But as soon as the car has started, the alternator kicks in, and the battery stops its supply. The dipping of the lights at this point indicates a failing alternator. 

Have a mechanic check the alternator for any issues with the power supply. A failing alternator can get you stranded when it fails as the battery will have to step in and supply electricity to all the demanding parts of the car, which will drain it after a very short time. You can replace a failing alternator before it stops working completely.

Poor Grounding

The grounding wire supplies part of the electricity the headlights need to function correctly. Without it delivering enough power, the headlights do not produce the light they are rated to produce. This wire sometimes accumulates dirt and grime or damages, leading to a compromised connection point. 

A close-up of wires

Replacing this wire resolves the power issue to the headlights. Replacing it is a labor-intensive exercise, though, and needs the assistance of an electrical mechanic. 

Worn Out Alternator Belt

The alternator belt connects the engine to the alternator supplying it with energy. It then converts this energy to electricity distributed through the car to the various electrical components. Sometimes the alternator belt wears out in different parts, causing the alternator to receive energy in pulses as the belt slips and grips. 

A closer look at a car engine

This action of slipping and gripping will supply varying power to the car’s components. The headlights are one of the parts that get heavily affected, and you will see the lights dip and brighten with this peak and decline of power. Have your mechanic check if the belt has worn down and needs replacement when you have these symptoms.

Cracked or Leaking Headlight 

Compromised headlights also dim the lights coming from the bulbs. They achieve this dimming by condensing water onto the lenses. This water has made its way into headlight housing through cracks on the housing or through the openings in loosely fitted housing. 

A close-up of a broken car headlight

A cracked housing can be repaired using silicon or any other agent that can seal the crack if it is small enough. This solution is only momentary as you must replace the headlight to ensure it serves you well. A loose headlight only needs some tightening to work correctly again. You must open it and clean the condensation before sealing it tight.

Wiring Compromise

Your wiring can get compromised and affect the headlights. The wiring system has several parts, including a fuse, a relay, a switch, and the bulbs to complete the circuit. Rare occasions can have this wiring system compromised. Trying out a DIY project on this system is one of the things that can compromise this system.

A specialist running diagnostics on a car

Your electrician will have to do a diagnostics of the system to verify that it does not have any compromised parts causing the lights to dim. You would have to tell them if you compromised this system while adventuring in a DIY project to make it easier for them to troubleshoot. 


Your headlights need to perform at their best at all times when you are driving. Having these headlights grow dim can affect your driving ability and compromise your safety. If you see your headlights grow dim, you can try and self-diagnose, but if unable to, seek the help of professionals to help you get to the root of the problem.

You can quickly resolve some of these dimming problems with little know-how, while others require the help of a professional. 

Have you gotten dim headlights at one point? How did you handle this problem, and did it eventually go away with your solution? Please tell us in the comments section down below.

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