Informational Guide

Why Are My Headlights So Dim?

The car headlights are needed to maintain optimal visibility at night and during inclement weather. When they start to dim, you need to know what’s going on. Why are my headlights so dim?  

There are several causes to consider. In this guide, we cover what causes dim headlights and how to fix dim headlights. We also answer when should you dim your headlights? 

Burnt Out Bulb 

Why is one headlight dim and the other bright? The most common issue is that one of the bulbs has burnt out or is dying. Of all the potential causes, this one is the easiest to fix. It simply requires that you put a new bulb in place of the burnt-out one.  

However, you might be able to replace it before it goes out completely. If you are paying attention, you will notice that one starts to get dim in comparison to the other side. Thankfully, you shouldn’t need to replace the bulbs often, so this should be a rare occurrence.  

Aging Headlight Lenses 

Do headlights dim over time? The bulb itself is only going to become dim if the bulb is burning out or there is an electrical issue. If the bulb seems to be burning just as bright as ever, but the beam still doesn’t shine through the lens completely, it could be time to look at the lenses.  

Just like most other car components, the headlight lenses can simply start to wear out. If there are scratches and blemishes on the lenses, these imperfections could cause the light to shine less brightly. It’s possible to restore some headlights, but if they are really old, you might decide that replacing them is a better option.  

Lens Oxidation Or Yellow Lenses 

Why are my car headlights dim? Sometimes, it is simply due to oxidation. The acrylic material that the lenses are made from can chemically react with the UV rays coming from the sun. This reaction leads to oxidation, which causes a yellow, cloudy or foggy lens. Also, because of the opaque condition, the light coming from the bulbs won't pass through as easily. If you've recently replaced the bulbs thinking that would solve the dim beam, but you are still in the same boat, it could be due to oxidation of the lens instead. 

With headlight restoration, you can clear up the headlight lens. You don’t even need to spend a lot on at-home restoration kits. There are also professional body shops that offer a full detailing service if you prefer to have someone else do it for you.  

Wiring Issues 

The headlight bulbs are powered by several different electrical components working in harmony. If a fuse has blown or there is an issue with a wiring harness, the bulbs could be out, or you could notice performance problems.  

While this issue seems easy to fix, it can become complicated in a hurry. Replacing a blown fuse isn’t an issue, but tracking down an electrical system fault and repairing it can be. Sometimes, it makes sense to get help from someone that has experience working with the electrical systems. Visit a professional if you need help walking through an electrical diagram and figuring out where each wire belongs.  

Wrong Setting 

The modern headlight allows for several different settings. If the headlights appear dim, there’s always the chance that you don’t have it on the right setting. Take a second and look at where the light switch is located. It’s possible that you’ve accidentally bumped the controller and turned them to an unusual setting.  

You can check the owner’s manual to understand what all of the signs are on the headlight controller. Practice in front of a garage door if you are unsure what each one means. If you have automatic headlights, you will also want to read up on how to override the system when needed.  

Bad Alternator/Loose Alternator Belt 

The headlights need power from the car to run. When the engine isn’t running, the headlights can still be on, but they receive power from the car battery. However, when the car is running, the alternator is responsible for powering the headlights. If there’s an issue with the brightness, one of these systems might be failing. 

When the alternator begins to fail, you might notice other issues. For example, the electronics inside the car might start to act erratically. Additionally, the car battery is going to die since the alternator won't be able to recharge it while you drive. Unfortunately, some people don't even find out that the alternator is bad until they have replaced a battery when it wasn’t needed.  

causes of dim headlight

Why Is One Headlight Dim And The Other Bright? 

Why are my LED headlights dim on one side but not the other? If you notice that one headlight is duller than the other, there are a couple of possible culprits.  

For starters, it could just be an old bulb. If the headlight is old, it might be time to replace it. It could also have to do with the installation. Is it possible that you put it in the wrong way or used the improper amount of wattage?  

There’s also the chance that the one headlight is misaligned, so the bulb is shining in the wrong direction. Of course, it might have to do with the lens and nothing to do with the bulb. Check the lens to see if it has become foggy and oxidized. If so, you can use a headlight restoration kit to make it clear again.  

one headlight is dim

People Also Ask (FAQs)

Why do my headlights dim when I hit the brakes? 

There could be a wiring or electrical issue to look at. When you press the brakes, the car needs to pull more power to the brake light, which can pull from your headlights.  

When should you dim your headlights while driving? 

When must you dim your headlights for oncoming vehicles? Driver tests commonly teach that you want to dim your high beams within 300 to 1,000 feet of oncoming traffic, but the laws are different in each state.  

Why are my HID headlights so dim? 

Over time, HID bulbs are known to lose some intensity. However, it could also be caused by a mechanical issue or a dirty headlight lens that needs to be restored.  

Do halogen bulbs lose brightness in car headlights? 

In general, halogen bulbs will retain the original brightness until they start to die. However, there could be misalignment concerns or electrical wiring problems that are creating dimness.  


Whether you are trying to figure out how to fix dim headlights on a Cadillac SRX or you want to know how to dim LED headlights, this guide should have provided you with some concrete answers. Knowing when to dim your high beam headlights and when it's time to replace the bulbs are both imperative so that you can ensure maximum visibility in any condition.