Gray hair is sometimes considered a sign of wisdom and farsightedness. The gray of the cover lens of a car headlamp is something entirely different. The sight is not very far at all. The gray veil does not only cost light. That wouldn’t be a serious problem. But the milky surface acts as a diffuser, thus refracting the light. The headlamp no longer shines in the direction actually assigned to it. Less light arrives at the important points of the road and more at unwanted ones. Glare is the result.
Result of a cleaning frenzy
But why do headlamp lenses become dull, gray or otherwise discolored? There are a few natural causes for this. Fine sand, in combination with wind, is an effective abrasive whose misdeeds can be easily observed by holidaymakers on dry Atlantic islands. The sea salt, also blown away by the wind, probably does the rest. Extended and frequent journeys on dusty roads and paths are therefore not good for headlamps.
However, there are no major concerns in this respect, as the far more important cause of worn cover lenses is excessive cleaning and misunderstood care. Some people think that the light from the headlight shines through a glass pane. And glass is so hard that it can withstand fly sponges and other aggressive cleaning methods. But that was true a long time ago. Today’s cars all have headlights with plastic polycarbonate lenses. Incidentally, it is not due to the stinginess of car manufacturers, but to pedestrian protection in the event of accidents. Polycarbonate does not splinter. It’s even more expensive than glass. These plastic discs are additionally coated with a lacquer. And it does not react well to rough cleaning rites. It is softer than car paint and the usual polish is already getting to it. A few wrong treatments and the paint comes off. After such a treatment, the headlamp at first has a pore-deeply clean look and high-gloss effect. After a short time, however, an initially only dull, later increasingly grayish sheen appears. This is like a metallic paint that no longer has a top coat. In the case of the headlamp, however, not only the gloss is missing, but also the UV protection that the coating offers. Sunlight can attack naked polycarbonate unfiltered.
If you call for help in internet forums, you will get plenty of tips. Polishing with baking powder is recommended. Others swear by toothpaste. The car will certainly not get cavities after the treatment and whether fluorine compounds damage the headlamp remains to be investigated. What is certain, however, is that enamel is much harder than varnish and polycarbonate. The abrasives in toothpaste are too aggressive for the latter. In short, all polishing methods only make things worse in the long run.
Less is more
So not taking the spotless cleanliness at the front of the vehicle too seriously is a good plan to keep the headlights in good condition. If you still want to polish, you should use a soft cloth and ordinary car shampoo. Even simple detergent does the trick. Some caution regarding cleaning agents is also appropriate if the car has a headlight cleaning system. Additives to wash water and antifreeze should be especially suitable for polycarbonate. All is good if the packaging notes it.