„Help, my headlights have fogged up!“ „How do I get rid of the moisture?“ These and other questions are among the one we hear most often. So it’s about time we took another long hard look at the phenomenon of fogging. That’s the name lighting experts have given to the effect you see when condensation builds up on the inside of the headlight lens.
1. What causes fogging?
All modern headlights are ventilated through small holes at the top and bottom. Ideally, they allow a gentle flow of air through the enclosure. If there was no ventilation there would be no way for the condensation ever to disappear. However, this flow of air can also allow moisture to enter the headlight. And then the same thing happens to the glass in the headlight as happens to the windows in a car when it’s cold outside and warm inside. You get a thin film of condensation.
2. Is fogging something really bad?
No. As we said, it’s just like your windows misting up. And in the same way, it disappears of its own accord in most cases. The only difference is that inside the car you can switch on a fan to get rid of the condensation quickly, whereas there is no fan in the headlight, except in those fitted with LEDs. There is a source of heat, however, which can speed up the drying process, namely the headlamp. So if you drive with your lights on you will have fewer problems with fogging. Xenon lamps produce less heat than halogen lamps so it will take a little longer for condensation to disappear from xenon headlights.
3. Is fogging a good reason to make a complaint?
No. Just as you wouldn’t make a formal complaint about mist-ed up windows. Once the condensation has cleared everything will be normal again and there will simply have been a short time when your headlights did not look their best.
4. Does fogging have any adverse effects on the light?
This would only be the case if the condensation extended the part of the lens through which the light from the headlamp is emitted. It would then cause the light to be unevenly distributed, resulting in glare for oncoming drivers. Generally speaking, however, condensation affects only those parts of the lens that are outside the light emission zone. Condensation particularly likes to collect at the bottom in the sharp-angled corners that designers so love to create. Ventilation has a hard job reaching these places. This is why you may even see droplets of water there.
5. What can I do to prevent fogging?
It is not possible to prevent it entirely. In fact, most car manu-als say precisely that. Humid summer days and cold winter days provide ideal conditions for this phenomenon that so many car owners find unattractive. But there are a couple of ways to minimize the risk. The one most likely to succeed is to drive with your lights on all the time. If fogging still occurs then the tips we have already mentioned will help speed up the drying process.
6. The condensation won’t go away. Is there anything I can do?
Sometimes, and in certain cars, it can take quite a long time. If it’s really bad you can use a hair dryer. Obviously you have to be careful how you use it. Don’t direct it at any plastic components as there’s a risk you might dam-age them. Ideally it’ll be enough just to heat up the head-light from the outside but it’ll be quicker if you can direct the hot air into the headlight from the engine compart-ment. To do this, remove the cover as if you were about to replace a lamp.Some workshops have even started using silica pads to dry out the condensation. You’ve probably seen them in the packaging for electronic items. They can only be used once and should not be kept per-manently in the headlight. A couple of hours with the car stationary should be enough. Don’t put silica pads in the reflectors, however, because they can easily get stuck there.
7. Can I improve the ventilation for the headlights, for example by making more holes or by leaving the cover off at the back?
No. In most cases this would just make the problem worse because the flow of air through the enclosure would be compromised. There would also be a much greater risk of dirt getting into the headlights. And dirt doesn’t disappear by itself. There are some headlights that are not exactly well designed, and some that are installed with less than optimum ventilation. Perhaps that is the reason why some manufacturers have issued instructions on how to install additional tubes to improve the exchange of air. Changes to the ventilation holes also fall into this category. It’s best if you ask your official dealer.
8. Should I try to open up the headlight to remove the moisture?
No way! The risk of breaking something far outweighs the minor irritation of the headlights not looking their best. And anyway the adhesive between the lens and the en-closure is really strong. You may have come across the „oven trick“. This damages the internals and may distort the enclosure.
9. I gave the engine a wash. Now there are gray smears in the headlights.
This is residue from the detergent used. The high-power jets in the car wash forced some of it into the headlights. Unlike pure water that has condensed from humidity in the air (in other words fogging), detergent deposits will not disappear of their own accord. So never aim a jet of water directly at a headlight. Not even from the outside.
10. There‘ a few centimeters of water in my headlights.
That’s not fogging. In most cases this is caused by a small crack or a broken seal. In a few cases it may be because a hole is blocked up. There are various reasons for this. Insects have been found in the holes. And dirt is a com-mon cause. Workshop mechanics have even come across clever people who have stopped up the holes with seal-ant, preventing water from draining out.
When it comes to fogging and moisture in headlights you can do more harm than good. So our advice is to ignore it in the first instance.