photo by Hari Nandakumar

Why Are My Headlights Getting Dim?

There are several reasons why your headlights are getting dim. The problem could be due to corrosion, light bulb problems, and even poor eyesight.

Driving home the other night, I noticed my headlights were dim. The road was darker than it should be. Other vehicles had lights that beamed brightly and illuminated the way. While I could still see ahead of me, there was a lot of squinting, and I looked forward to passing under street lights. When I got back to my house, I remembered the last time it rained the roads seemed quite dark. And then I wondered Do headlights get dimmer over time? Maybe there’s something wrong with my car? Perhaps there’s something wrong with my eyes?

The Danger Posed By Dim Headlights

Headlights that don’t function properly are a real threat to the driver, their passengers, and everyone in the vicinity. Consumer Reports (CR) reported in 2018, the dangers they pose.

Over time, the plastic coating on headlights can become so clouded or yellowed that they give off only 20 percent of the light they had when you first bought the car, the AAA study says. That puts drivers at great risk of crashes as their car ages.

Only 20 percent! That number is jarring. Drivers are distracted enough. We don’t need poor night visibility to add to the dangerous mix!

CR states headlights may start to deteriorate after 3–5 years. Many cars on the road are over three years old, and that means there are probably a good number of them with dim lamps.

Eye Sensitivity To Light

Dim headlights may be the cause of you not seeing things clearly at night. However, there is another possibility. The older the driver is, the less sensitive they are to light. Harvard Medical School writes the problem is very real.

It doesn’t get that much attention, but diminished night vision is one of the most common problems of the aging eye. Rare is the person who, starting around age 40, doesn’t dread driving at night. Roadway crashes are the leading cause of on-the-job fatalities among older workers in the United States; safety officials say that poor night vision could be partly to blame. And a certain — if unspecified — number of falls and stumbles at home are probably related to the inability of the older eye to pierce the gloom.

There are a few reasons why an older eye isn’t as sensitive to light. There are less light receptive cells (rods) in the eye. The pupils of older drivers are smaller than those of younger ones, and that means less light gets in. The lense may become cloudy. And the ability to shift from lighted conditions to dark ones gets worse as we get older.

Bad Ground Wire

A faulty wire couldbe the cause of your dim headlights. You may remember from high school science class electricity needs to travel in a complete circuit for it to do the job. A ground wire completes that circuit in your vehicle. A lousy ground wire will cause those headlamps to burn less brightly. explains.

Problems with the ground circuits to headlights can cause them to dim or not operate at all. The ground circuit provides a path for the electricity from the headlight to return to the negative terminal of the vehicle battery. The ground wire is normally a short wire attached to the vehicle chassis near the headlight. The vehicle chassis itself provides the remainder of the return path to the vehicle battery.

Your local mechanic can see if your ground wire is working correctly.

Battery Terminal Or Headlight Socket Corrosion

Corrosion of the bulb terminals and/or battery terminals may be the source of your problems. Corrosion is a process where metal deteriorates. Rusting occurs when iron or a metal with iron in it interacts with oxygen over time. When battery terminals corrode, it’s due to hydrogen gasses escaping from the battery and interacting with the metal that makes up the terminals. Headlight sockets may corrode due to exposure to the elements or gasses leaking from the bulb. In both circumstances, the residue created by corrosion interferes with the electricity passing into the headlight, making it dim.

Light Bulb Problems

Issues with the bulbs themselves can cause the lights to lose their luster. The Know How Napa Blog reports the older the bulb is the greater chance it is to be dim.

Although LED and HID headlights are becoming more common, the majority of cars and trucks still make use of halogen bulbs as their primary light source. In theory, halogen lights are designed to retain almost 100 percent of their initial brightness over time due to how tungsten particles in the filament are recycled during the illumination process.

In reality, however, there can be many factors affecting how well a halogen bulb illuminates as it ages, including inefficiencies in power usage, design flaws that pull too much power initially to appear brighter out of the box (prematurely wearing out the bulb) or loose filaments that can make it harder to focus the light.

Headlight Lenses Are Hazy

The problem may not be with your eyes, the bulbs, or the electrical system. The casing around your headlights can be the problem. Popular Mechanics explains:

Most headlight lenses are made of polycarbonate plastic. This strong plastic is perfect for taking on harsh road conditions without breaking, which you definitely want, but it doesn’t play well with the sun. To protect it initially, manufacturers coat the lenses with a UV protective film. But over time this film is destroyed by UV rays, allowing the plastic to oxidize.

The good thing is there are simple ways of restoring your lenses!

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