Cloudy or yellow headlights: restore them or replace them?

Almost every car built since the 1990s uses polycarbonate headlight lenses instead of glass. Polycarbonate is light and shatter resistant, but it yellows in sunlight, so manufacturers coat it with a thin UV-resistant hard coat. That coat is what wears out. Once sun, sand, car-wash brushes and road grit wear through it, the plastic begins to oxidize and the yellow haze builds year after year.

The problem is not only looks. A cloudy lens scatters light instead of focusing it into the beam pattern. In a 2018 study following federal headlight standard FMVSS 108, AAA had an accredited lab test the headlights from two roughly 11-year-old sedans. The degraded low beams produced about 22 percent of the light of new ones. AAA also noted deterioration can start in as little as three to five years.

Restoration and replacement are both legitimate fixes, and they are not equal. Knowing which one you need saves either money or night vision.

Symptoms

• Lenses look yellow, foggy or frosted from outside
• Low beams seem weak and spread poorly even with new bulbs
• Rough, sandpaper-like texture on the outside of the lens
• Small cracks or crazing in the plastic
• Haze or water droplets visible on the inside of the lens
• One headlight looks clearer than the other after a previous repair

Likely causes and what they cost

Costs are typical South Florida ranges for parts and labor, for budgeting only.

What you can check yourself

1. 1
   Find out if the haze is outside or inside

   Wet the lens with water. If the yellow briefly clears while wet, the damage is on the outer surface and restoration should work. If it stays cloudy or you see droplets behind the plastic, the problem is inside.

2. 2
   Run your fingernail across the lens

   A rough or gritty surface means oxidation. Feel for cracks or deep pits, which restoration will not remove.

3. 3
   Do a beam test against a wall

   At night, park about 25 feet from a garage door or wall on level ground with low beams on. Look for a sharp top edge on the beam and even brightness side to side. A smeared, dim or uneven pattern points to lens or aim problems.

4. 4
   Check the bulbs before blaming the lens

   Halogen bulbs dim with age, and one may be the wrong type. Compare both sides. Bulbs are cheap to replace and often worth doing at the same time as a restoration. Let bulbs cool before touching them, and do not touch the glass of a halogen bulb with bare fingers.

5. 5
   Mask the paint if you try a kit

   Use two or three layers of painter's tape around the lens. Sanding discs slip, and scuffed bumper paint costs more to fix than the headlight.

When to take it to a shop

• If the haze is inside the housing, or there is visible water, you need replacement assemblies, not restoration.
• If your car has LED, adaptive or self-leveling headlights, have a shop handle replacement and aiming. These often need a scan tool to initialize.
• If you restored the lenses and night visibility is still poor, have the headlight aim checked. A shop with an aiming tool can do it in minutes.
• If you plan to keep the car several more years, ask for a quote on OEM assemblies. AAA found they restored 100 percent of original output, while restoration reached about 70 percent and aftermarket replacements 83 to 90 percent.

The Florida factor

Florida sun is hard on polycarbonate. Headlights face forward and upward, so a car parked nose-out in an open lot catches direct sun on the lenses for hours every day. Many South Florida cars show yellowing by year four or five, a little faster than the low end of AAA's estimate. Parking nose-in to a wall or hedge, or under a carport, keeps the lenses out of the afternoon sun.

Weak headlights matter more here than you might expect. Florida law, s. 316.217, requires headlights not only from sunset to sunrise but during rain, smoke and fog. That means the daily summer storm on I-95 or Glades Road is a headlight situation even at 4 p.m., and lane lines on wet asphalt are hard to see with scattered light. Sand blown off the beach and A1A also pits lenses faster on cars that live east of the Intracoastal.

Restored lenses last longest with protection. After a restoration, a quick wipe-on UV sealant every few months, or a clear protective film over the lens, extends the result. Without it, a restoration in Boca can yellow again within a year or two.

Notes for specific makes

• Mercedes-Benz: Many Mercedes models from the last decade use LED or multibeam adaptive headlights. Replacement assemblies can cost well over $1,500 per side before labor, which makes restoration and lens protection especially worthwhile while the housing is still sealed.
• Audi: Matrix LED and full LED units on many Audis are expensive to replace and require coding. If the outer lens is only oxidized, restoration is far cheaper. Internal condensation, however, needs dealer or specialist diagnosis.
• Honda: Older Civic, Accord and CR-V models with halogen projector or reflector lamps are classic candidates for restoration. Aftermarket assemblies are inexpensive, but AAA's testing suggests some may produce more glare or less output than OEM.

Frequently asked questions

More on this job: Detailing in Boca Raton, costs and how to choose a shop