Bright town centre, dark suburbs, tired lenses
Central Croydon is one of the most brightly lit places in south London. Wellesley Road, the area around Croydon Minster and the Whitgift Almshouses, Fiveways and the retail stretch of Purley Way all throw out so much ambient light that your own headlamps barely have to work. That is a trap. Drivers get used to judging their lights on roads where the street lighting is doing the job, then take the A235 Brighton Road out through South Croydon or head for the suburbs and find the beam has nothing left in it.
What has happened is that the thin ultraviolet hard coat on the outside of each lens has broken down, and the polycarbonate underneath has oxidised to a yellow-brown haze that scatters light rather than projecting it. It is gradual, so nobody notices the day it becomes a problem. The usual prompts are an MOT comment, a passenger remarking how dim the road looks, or finally seeing the car head-on in daylight and realising the lamps have gone brown.
There are two honest limits worth stating. First, a headlamp that is deteriorated enough to reduce light output is an MOT defect and a poor beam pattern gets noted at test, so a badly clouded lens can fail, but restoration is not a guaranteed pass because the tester judges the lamp on the day. Second, the result is not permanent. A properly applied UV-stable clear coat over a fully refined surface should give you several years, and a car kept under cover will do better than one parked on a 20mph terraced street all week.
On the day we assess whether the fault is outside or inside the unit, mask the paint and trim, wet sand through progressively finer grades, machine polish, apply the clear coat and check the beam pattern and aim. The drive over is the A232 west through Waddon and Beddington to Wallington and north up London Road, about 15 minutes. Collection and delivery can be arranged if getting the car to Hackbridge is the awkward part.