They can. A WoF inspection assesses headlight condition and light output, not haziness on its own, so mild cloudiness usually passes. Heavy yellowing or oxidation that noticeably reduces output can fail, and so will a cracked lens or moisture inside the housing. Lighting faults are the most common WoF failure category in New Zealand.

NZTA data consistently puts lighting and signalling at roughly 35 to 40 percent of first-inspection failures — ahead of tyres, brakes and everything else. Most of those are bulbs, but degraded lenses contribute.

If your WoF is due and your headlights look tired, restoration is far cheaper than a failed inspection and a re-test. If you have already failed, you have 28 days to get it sorted and return for a free recheck at the same inspecting organisation.

Headlight restoration at Mats Detailing starts from $100 per set for a polish and sealant on mildly hazy lenses, and from $200 per set for full sanding and a UV clear coat on heavily yellowed ones. Headlight paint protection film is available from $200 per set.

The difference between the two is how far the oxidation has gone. Light haze polishes out. Yellowed, chalky lenses need the degraded outer layer sanded back in stages before polishing, which takes considerably longer.

We will tell you which one your car needs from a photo. Send us a clear shot of both headlights in daylight and we will quote without you coming in.

A polish and sealant typically holds up for around six to twelve months before the haze starts returning. Sanding with a proper UV clear coat lasts considerably longer — generally two to four years, and longer again on a garaged car. Headlight PPF outlasts both.

The variable that matters most is UV protection. Factory headlights have a UV-resistant coating from new, and once that has been sanded away, anything that does not replace it leaves bare polycarbonate exposed. Bare polycarbonate yellows fast.

That is the whole reason the cheaper option is cheaper. A polish and sealant is a maintenance treatment; sanding plus UV clear is a repair.

Modern headlight lenses are polycarbonate with a thin UV-resistant factory coating. UV exposure, road grit, bug splatter, harsh washing chemicals and general weathering break that coating down over years. Once it fails, the plastic underneath oxidises, and that is the milky yellow haze you see.

Cars parked outdoors degrade faster than garaged ones, and north-facing windscreens get more sun on the lenses. In New Zealand it happens faster than in most countries — our UV levels are among the highest in the world, roughly 40 percent stronger than comparable northern-hemisphere latitudes.

It is a surface problem, which is why it can be repaired. The lens itself is usually fine underneath.

Short-term, yes; long-term, rarely. Most kits include an abrasive and a polish but no UV clear coat, so you remove the oxidised layer and leave bare polycarbonate exposed. It looks great for a few weeks, then yellows again faster than before because the factory UV coating is now gone too.

The toothpaste trick works on the same principle and has the same problem. You are abrading the surface with a mild abrasive and protecting nothing.

If you are going to do it yourself, the one thing that matters is finishing with a proper UV clear coat rather than a wax or a general-purpose sealant. Without that step you are making next year worse.

Usually, yes. Even severely yellowed lenses generally restore well, because the damage is in the outer layer of the plastic rather than through it. The process is staged sanding to remove the degraded material, multi-step polishing to return optical clarity, then a UV clear coat.

What cannot be fixed: cracked lenses, moisture or condensation inside the housing, a flaking internal reflector, and failed LED or projector units. Those are replacement jobs and we will say so rather than take your money.

Peeling factory coating is a middle case. It restores well but needs all of the old coating removed first, which takes longer than ordinary oxidation.

Usually by a wide margin. A replacement headlight assembly on a modern car frequently runs into four figures per side once you factor in LED or adaptive units, and that is before fitting. Restoration is a fraction of that when the damage is external.

Replacement makes sense when the lens is cracked, the housing is letting water in, the reflector has deteriorated or the electronics have failed. No amount of polishing fixes any of those.

Send us a photo before you order parts. It costs nothing to find out whether yours can be saved.

Yes, noticeably on badly oxidised lenses. Oxidised polycarbonate scatters and absorbs light rather than letting it through cleanly, so output drops and the beam pattern softens. Clearing the lens restores both.

The difference is most obvious on unlit rural roads and in rain, which is most of the Waikato in winter. Drivers often describe it as feeling like new bulbs rather than new lenses.

It will not fix a genuinely dim headlight caused by an aging bulb, a poor earth or a failing ballast. If the lens is clear and the light is still weak, the problem is electrical.

It is the best long-term answer, particularly on a new car. Headlight paint protection film protects against stone chips as well as UV, and it means the lens underneath never oxidises in the first place. We fit headlight PPF from $200 per set.

On a new vehicle it is the obvious time — the lens is perfect, so film simply preserves it. Headlights are also one of the most commonly stone-chipped parts of a car on open roads, and a chipped lens cannot be polished out.

On restored headlights, film goes on after the restoration and protects the result. It is more expensive than a UV clear coat but it lasts far longer.

Eventually, yes — but how soon depends entirely on what was applied afterwards. A polish and sealant will haze again within a year. A proper UV clear coat holds for years. Headlight PPF effectively stops it for the life of the film.

You can slow it either way. Park out of direct sun where you can, avoid harsh cleaners and automatic brush washes on the lenses, and wash them with the same pH-neutral shampoo you use on the paint.

If your headlights have gone yellow quickly after a previous restoration somewhere else, it almost certainly means no UV coating was applied.

Before publishing: the two price placeholders, the durability ranges in question three, and the mobile split in question eleven all need confirming. The WoF answer is worded carefully to be accurate — please do not let anyone tighten it into "cloudy headlights fail a WoF", because that is not what the rules say