The Headlights Work — But Do They Still Illuminate the Road Properly?

A headlight doesn’t have to burn out to become bad.

On an older car, both headlights may still work perfectly well, while the driver sees significantly less at night than when the vehicle was new.

This is one of those problems that develops so gradually that the driver often does not even notice it.

The bulbs work. There is no warning on the instrument panel. When you stand in front of the car, both headlights are on.

And yet, night driving is no longer the same. The road seems darker, the low beams seem to reach less and less far, and on unlit roads you increasingly feel the need to switch on the high beams.

The problem may not be your eyesight.

Your headlights may simply have aged.

Why this is a bigger problem here than in much of Europe

There are two reasons, and both are particularly relevant to Serbia.

The first is the age of the vehicle fleet. According to data from the Road Traffic Safety Agency, the average vehicle in Serbia is more than 16 years old, while more than 80% of passenger cars are over ten years old. In the European Union, the average is around 12 years.

This means that a huge proportion of our cars are already in the age range where headlight degradation is no longer merely a theoretical possibility, but something that should be expected.

The second reason is the law. Article 77 of the Road Traffic Safety Act requires low-beam headlights or daytime running lights to be switched on during daytime driving.

In newer vehicles, this is handled by dedicated daytime running lights (DRLs). But in an older car without DRLs, the driver uses the low beams during the day — which means that the halogen bulbs and the entire headlight assembly are operating practically every time the vehicle is moving, not only at night.

The same headlight, the same number of years, but many more operating hours than in countries where lights are not used during the day.

That is why the fact that some headlights can begin to deteriorate after only three to five years — a period cited by the American Automobile Association (AAA) for halogen reflector headlights, depending on sun exposure — should not be considered an upper limit in our market, but rather a realistic starting point.

What actually changes over time

A headlight is not just a bulb.

For the light to end up where it belongs — on the road ahead of the vehicle — the entire system has to work properly: the light source, reflector or projector, lens, transparent headlight cover, electrical system and correct beam alignment.

Each of these components can lose some of its original performance over the years.

1. The transparent plastic is no longer completely transparent

On many modern vehicles, the outer headlight cover is made of polycarbonate.

It is lightweight and impact-resistant, but over the years it is exposed to UV radiation, high and low temperatures, road salt and dirt, chemicals, washing, and small impacts from sand and stones.

The protective coating can deteriorate over time, while the headlight surface may become yellowed or cloudy.

When that happens, some of the light is no longer directed properly onto the road but is scattered instead.

In an AAA study carried out in an accredited laboratory on the headlights of two popular sedans approximately 11 years old, heavily degraded headlights produced only around 22% of the low-beam light output of new headlights of the same type.

That does not mean that every ten-year-old headlight will lose that much light. But it does show how large the difference can become when deterioration is ignored for years — and it is worth remembering that the average car in Serbia is older than the vehicles used in that test.

In other words: the headlight is still on — but much less light is reaching the place where the driver actually needs it.

2. Components you cannot see from the outside can deteriorate too

A clean and transparent outer cover does not automatically mean that the headlight is in good condition.

Inside the headlight is a reflective surface whose job is to direct the light.

Over time, it can lose its original properties, become dull or suffer damage. Moisture inside the housing can also contribute to the long-term deterioration of the reflector and optical components.

With projector headlights, the problem may also be in the projector itself or the lens.

In that case, polishing the outer plastic will not solve the underlying problem.

3. A bulb does not have to burn out to become weaker — and the electrical supply may not be perfect either

There is a common misconception, particularly with older halogen systems:

“I replace the bulb when it burns out.”

However, a bulb can gradually lose some of its light output during use even though it continues to function. Lighting equipment manufacturers have been pointing this out for years and often recommend replacing bulbs in pairs before complete failure occurs.

Also consider what we have already mentioned: if you drive an older car without daytime running lights, those bulbs are also operating during the day. Their useful life is being consumed much faster than mileage alone might suggest.

That is why a large difference between an old and a new bulb does not necessarily mean the old one was “faulty.”

It had simply aged.

But even a new bulb is not always the solution.

Halogen bulbs are highly dependent on the voltage they receive. On an older car, oxidised connectors, poor grounding, ageing wiring or other electrical problems may cause a voltage drop — resulting in visibly weaker light output.

A good repair shop therefore will not only check whether the bulb works, but will also check the power supply when necessary.

4. Or perhaps the headlight is simply shining in the wrong direction

You can have a perfectly functioning headlight and a new bulb — and still have poor visibility.

If the headlight is aimed too low, much of the light ends up only a few dozen metres in front of the vehicle.

If it is aimed too high, it can dazzle oncoming drivers, while the distribution of light on the road is still poor.

In its review of research, the U.S. National Highway Traffic Safety Administration (NHTSA) identifies incorrect headlight aim as a factor that can reduce visibility when headlights are aimed too low and increase glare for other drivers when they are aimed too high.

In Serbia, this is not merely a matter of comfort. Headlight beam alignment is measured — beam setters used for this purpose are legally regulated measuring instruments, and the proper operation of lighting and signalling equipment is part of the mandatory vehicle inspection.

That is why headlight quality cannot be assessed simply by looking at the lamp.

What matters is where the light actually ends up.

Check your lights before someone else does

If your technical inspection is approaching, the lights are one of the easiest things to deal with in advance — and one of the items that commonly cause vehicles to be sent back.

Find a technical inspection centre or repair shop in your city at autokonekt.rs/lokacije.

LED and xenon: a different story, and a more expensive decision

Everything mentioned so far primarily applies to halogen systems, which are still the most common on our roads.

With LED headlights, the logic is different — and this often surprises drivers.

In many LED assemblies, the light source is not a replaceable bulb — the LED diodes are integrated into the headlight itself. When they weaken or fail, you do not replace a “bulb”; the entire assembly may need to be replaced, which can make a significant difference to the repair bill.

LEDs also lose some of their light output over time, only more slowly and less noticeably than halogen bulbs. Their degradation can actually be harder to notice because there is no obvious moment when a bulb suddenly burns out.

With xenon (HID) systems, there is another issue many drivers are unaware of: over the years, a xenon bulb does not only lose intensity — its light colour often changes as well, shifting towards a bluish or purple hue.

If you notice that your two headlights produce different colours, it is a clear sign that one light source is significantly older than the other.

The outer plastic, however, oxidises in the same way regardless of the lighting technology. A cloudy headlight cover on an LED-equipped vehicle will still scatter light — even though the driver may assume that because it is LED, “it must be fine.”

How can you notice that something is wrong yourself?

You do not need special equipment to spot the first warning signs.

Pay attention if:

▪ the headlight surface is no longer completely transparent
▪ one headlight appears brighter than the other
▪ the two headlights produce different light colours
▪ the low beams have noticeably less range than before
▪ at night you increasingly feel the need to use the high beams
▪ the beam pattern is uneven
▪ one headlight shines higher or lower than the other
▪ moisture regularly appears inside the headlight
▪ replacing the bulbs brings very little improvement

You can also perform a simple check on a flat surface in front of a wall or garage door.

Park the car a few metres away from the wall and switch on the low beams.

This test is not intended for adjusting the headlights yourself — proper adjustment requires the correct equipment and measurement. It is simply a way to compare the left and right headlights: are they roughly similar in height, beam pattern and intensity?

If there is an obvious difference, you know that it is worth having the system checked — and you already know what to discuss with the technician.

Does headlight polishing solve the problem?

Sometimes yes.

But not always.

If the main problem is oxidation and clouding of the outer polycarbonate surface, a properly performed restoration can significantly improve light transmission.

In the AAA study mentioned earlier, both professional and DIY restoration brought the average light output of the tested degraded headlights back to approximately 70% of a new headlight, while replacing the assembly with a new original unit produced the best result — a return to 100%.

There is also another side to that finding: both restoration methods produced more glare than was considered acceptable under the U.S. criteria used in the study.

In other words, polishing can restore the amount of light, but not necessarily its correct distribution — which is another reason to check beam alignment after restoration.

But polishing will not fix:

▪ a burned or damaged reflector
▪ a problem with the projector or lens
▪ an electrical fault or voltage drop
▪ incorrect headlight alignment
▪ an unsuitable or worn-out bulb

That is why it is important to identify the actual cause first and only then decide what needs to be repaired.

What about a more powerful bulb?

A common reaction is:

“My headlights are weak — I’ll install stronger bulbs.”

But if the light cannot pass properly through a cloudy lens or the reflector no longer directs it correctly, a more powerful light source does not solve the underlying problem.

You may simply end up with more scattered light rather than better road visibility — while increasing the risk of dazzling oncoming drivers.

A much more logical sequence is:

headlight inspection → check the bulb and power supply → inspect the optics → adjust the beam → only then decide what needs replacing.

Headlights age slowly. That is why the problem is easy to miss.

When a bulb burns out, you immediately know something is wrong.

With gradual headlight degradation, there is no such moment.

Today it shines slightly less brightly than yesterday. You do not notice the difference.

The same thing happens the following month and the following year.

Only when you get into a newer car and drive the same road at night do you think:

“Wow, this car has really good headlights.”

Maybe it is not just because the car is newer.

Maybe you have simply become accustomed over the years to headlights that are getting progressively weaker.

And during the autumn and winter months, when much more driving takes place in darkness, that difference is no longer simply a matter of comfort.

AutoKonekt advice

If you drive an older car and feel that you can no longer see the road at night as well as you used to, do not wait for a bulb to burn out.

Ask for the entire lighting system to be checked — the condition of the outer headlight surface, reflector and projector, the bulbs, the power supply and correct beam alignment.

Book a lighting system check with a trusted repair shop through autokonekt.rs.

Because the question is not simply:

“Do the headlights work?”

The far more important question is: “Do they still illuminate the road the way they should?”

Frequently Asked Questions

How long does a car headlight last?

A headlight does not have a fixed service life, but the outer polycarbonate surface often begins to show signs of deterioration after several years of sun exposure. AAA cites a period of three to five years for halogen reflector headlights.

The rate of deterioration depends on whether the vehicle is parked outdoors or in a garage, the climate and the way the car is washed.

Does headlight polishing really help?

It helps if the cause of the weaker light is a cloudy outer plastic surface. In the AAA test, restoration brought light output back to around 70% of that of a new headlight.

It will not help if the problem is in the reflector, projector, power supply or alignment — which is why the cause should be identified first.

Why is one headlight weaker than the other?

The most common causes are bulbs of different ages, uneven deterioration of the outer plastic, moisture in one housing, poor electrical contact or grounding on one side, or different beam heights.

A difference in light colour usually indicates that the light sources are of different ages.

Are headlights checked during the technical inspection?

Yes. The proper operation of lighting and signalling equipment is part of the technical inspection, while headlight beam alignment is checked with a beam setter, a device that is legally regulated as a measuring instrument in Serbia.

Do stronger bulbs solve the problem of weak headlights?

No, not if the cause is the headlight optics or incorrect alignment.

A stronger light source in a cloudy or poorly aimed headlight produces more scattered light, not necessarily better visibility, while also increasing the risk of dazzling other drivers.

What if there is moisture inside the headlight?

Occasional light condensation is normal on some vehicles and disappears after driving.

However, recurring water or visible droplets indicate that the sealing is not functioning properly, and over time this can accelerate deterioration of the reflector and electrical contacts.

It is worth having the headlight checked at a repair shop.

Sources

▪ Road Traffic Safety Act, Article 77 — use of vehicle lights
▪ Road Traffic Safety Agency — statistics on the age of the vehicle fleet
▪ AAA, “Headlight Replacement and Restoration Research” (2018)
▪ NHTSA — review of research on headlight alignment and visibility
▪ Rulebook on beam setters, Ministry of Economy of the Republic of Serbia