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Why Dim Headlights and Brake Lights Are Still a Hazard

Headlights on a car. Here's why dim headlights and brake lights are dangerous and can affect your ability to see the road.

“They still work, they’re just a little dim. What’s the point of replacing them before they burn out?”

You probably know someone who says or thinks that about their barely-lit headlights or brake lights. You may even be that person. We need to fix that. Your vehicle’s headlights are like your eyes. Dim headlights are like not being able to see very well. And unlike your eyes, dim headlights make other drivers less able to see you.Headlight

Oh, yeah — and that lack of vision is happening while you’re moving at anywhere from 25 to 70 mph. Not good. Especially if you or someone else gets hurt in an accident that happened because you couldn’t see them or vice versa.

Light Is Light, Right?

No, not when it comes to your vehicle. Part of the problem is that we’re conditioned by other lights in our lives. LEDs are binary. They’re on or off. CFLs and incandescent bulbs in our houses and workplaces, for the most part, don’t slowly go dim. They put out the light the package promises until the day they stop altogether.

In theory, your vehicle’s headlights and brake lights should deliver that kind of consistency, too. If they’re not — if you’re noticing you can’t see as much of the road at night as you used to — or the lamps just look dim when you’re standing outside the car and looking directly at them, there are some things you should check right away:

  • Are the lenses over the headlights getting cloudy? If so, clean them. Even really opaque plastic headlight covers can be improved with a rag, some toothpaste and good old-fashioned elbow grease.
  • Check the ground wire that attaches to your chassis. If it’s corroded, that could absolutely be reducing the power that’s going to your headlights. Clean that off with a wire brush.
  • A bad alternator or a loose alternator belt can show up in dimmer headlights. And there are other problems that come with either of those. Checking the alternator belt for wear, adjusting the tension of the belt and — if necessary — replacing the alternator can brighten your headlights considerably.

Or …

It could be your bulbs. Especially if they’re incandescent or even halogen headlamps. The filaments in incandescent bulbs can leave a brown or gray deposit on the glass of the bulb itself (you might see this at home, too — especially on bulbs that have been in use for a long time). And halogen bulbs, over time, can develop a film that reduces the light escaping as well.

If that’s the case, it’s time to replace the bulbs. And the good news is that bulb technology is a lot different today than it was just a few years ago, with choices in terms of whiteness and brightness that didn’t exist before. A small investment and a quick bulb swap can make a huge difference in what you can see.

Check out all the vision and safety products available on NAPA Online or trust one of our 17,000 NAPA AutoCare locations for routine maintenance and repairs. For more information on headlight bulb options, chat with a knowledgeable expert at your local NAPA AUTO PARTS store.

Photo courtesy of Wikimedia Commons.


Mike Hagerty View All

Mike Hagerty is an automotive journalist whose work has been featured on radio, TV, in print and online since 1997. He's the Publisher and Editor of, and contributes car reviews to the Los Altos Town Crier and Previous outlets have included KFBK and in Sacramento, California, the ABC television affiliates and Hearst-Argyle and Emmis radio stations in Phoenix, Arizona; AAA magazines for Arizona, Oklahoma, Northwest Ohio, South Dakota and the Mountain West and

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