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Car headlights fogging up?1

Sometimes in the early morning, we will find that the surface of the lampshade (optical mirror) of the car light is foggy. At this time, don't doubt the quality of the car lights, and don't wonder whether the lights are filled with water. There is fog in the car lights, which is normal.

Many people think that car headlights are completely sealed and cannot fog up. In fact, not only cars worth over RMB 100,000 will fog up, but also cars worth over RMB 400,000 will fog up. Even for a million-dollar luxury car like Tesla, fogging up the headlights is a skill that you can't see.

Of course, the more advanced the car, the headlights will definitely be designed to prevent fogging.

First of all, everyone must understand that car lights, whether they are headlights or taillights, are not airtight. Although the lampshade is surrounded by a waterproof seal when it is installed, each lamp will have a breathable design.

The reasons for the breathable design are, firstly, to allow air to flow to cool down the car lights, and secondly, to adjust the air pressure balance inside and outside the car lights. When the car lights are on, the temperature inside the lamp is very high, and the water vapor in the air is heated and vaporized; when the car is turned off and the lights are extinguished, the temperature inside the lampshade drops sharply, and the water vapor condenses on the wall of the lampshade to form fog. This is the breathing function of the headlights.

In areas with humid air and large temperature differences between day and night, the phenomenon of headlight fogging is most obvious. Generally speaking, the fog will be evaporated by the heat of the engine and sunlight soon after the car is restarted; if the headlights are turned on, the fog will be evaporated within an hour.

When the car lights are designed to be airtight, there will be at least one ventilation hole behind the lamp housing, that is, behind the base of the car lights. These ventilation holes are responsible for the circulation of air inside the lampshade, cooling and balancing the air pressure.

According to the principle of thermodynamics, for every 1°C increase in air temperature, its volume expansion rate is 1/273. For example, traditional halogen headlights can reach a temperature of over 70°C after one hour of continuous exposure. Therefore, to ensure that the air pressure in the car lights does not become too high and cause damage to other parts, a breathable design is required.

At the same time, in order to ensure that the lampshade, that is, the light distribution lens, will not melt due to excessive temperature, air circulation is required to cool down. It can be said that the design of the ventilation holes is crucial to ensure the normal operation of the car lights and extend the life of the car lights.

When designing the headlights of luxury cars, air circulation and temperature balance will be taken into consideration in their shape. For example, if the headlights of a car have a sharp-angled design, then this flowing dead zone will be difficult to be heated by the light, thus forming a temperature difference with the area that can be illuminated by the light, easily forming fog, and not easily being evaporate.

In addition, due to the popularity of xenon lamp and LED headlight technology, it is difficult to quickly evaporate fog solely by the heat of the light source. The power of halogen headlights is 55W, while the power of xenon lights is 35W, and the heat output is not as good as that of halogen headlights. In addition, xenon lamps and LED lamps generally have lenses, so the light source is more focused, making it more difficult to evaporate the fog in the corners of the lampshade.

Therefore, in order to reduce the formation of fog in the car lights, the shape design of the car lights is very important, and it is necessary to ensure that relatively complete air convection can be formed within the lamp body. At the same time, the bonding between the lampshade (optical lens) and the lamp housing should ensure tightness to prevent air from entering here.

The ventilation holes generally have breathable covers or U-shaped rubber tubes to prevent rainwater from entering, and the ventilation holes themselves also have a breathable membrane (sponge or non-woven fabric) to filter part of the water. However, since the diameter of water vapor molecules is 0.0004 microns, ordinary breathable membranes cannot stop it at all.

When designing the lights of luxury cars, in order to reduce the generation of fog, they will try to avoid the existence of flow dead zones, which may compromise the aesthetics; the inner wall of the lampshade will also be coated with special masking paint. Avoid fog from adhering to it; at the same time, the distribution of the positions of the ventilation holes on the lamp housing should also be conducive to the rapid flow of air; in the selection of filters, micron-level breathable films with extremely small pores will also be used to block the air as much as possible moisture in it.

Of course, the amount of water vapor is relative. How much moisture can be blocked also depends on the air pressure. If the air pressure is high, water molecules will be squeezed in.

However, if the pore size of the breathable membrane is too small, it will hinder breathability. The best solution should be: the pore size of the breathable membrane should be between the diameter of water vapor molecules and the diameter of the smallest fog molecules present in rainwater (20 microns), which can not only block the entry of fog in the air on rainy days, but also ensure breathability.

This high-performance waterproof membrane was first developed by the American Gore Company using polytetrafluoroethylene (PTFE) material. Japan's Nitto Denko Co., Ltd. (NITTO) also has such products.

For some car lights, because the quality control of parts is not strict enough, the fog phenomenon is serious and lasts for a long time. In this regard, the headlight can be disassembled, the fog water can be manually cleaned, and the sealing ring can be replaced with a new one. If it is a quality problem, the headlight assembly should be directly replaced with a new one during the warranty period. Never use a heating lamp to bake or pour hot water on the lamp body, as this will damage the physical properties of the lampshade.

It should be noted that to clean the fog in the headlights, it is not necessary to completely disassemble the headlights. In fact, if we have the tools, we can do it at home: remove the headlight assembly, open the back cover, blow hot air inside to let the mist evaporate, and then tighten the back cover; buy sealant and use a syringe to line the lampshade and lamp shell. Just glue the edges.

In addition, we must also distinguish the difference between fogging of car lights and water ingress of car lights. If you find traces of water flowing on the inner wall of the lampshade, it is possible that the car lamp has water in it. There are many reasons for water in the car lights, such as aging of the sealing ring, rupture of the breathable film, not tightening the back cover of the lamp housing, etc. If the headlights are flooded, the headlights should be disassembled and repaired.

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Car headlights fogging up?1 1

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