Moisture in the air will enter the headlight through the vent pipe and adhere to the lampshade. As the water vapor gathers, water droplets will flow down the lampshade. This situation is mostly caused by large temperature differences, and this phenomenon is most likely to occur in winter and rainy seasons. After the car lights are turned on for a period of time, the fog will be discharged out of the lights through the vent pipe along with the hot air, which will basically not damage the headlights and electrical circuits.
In this situation, the driver’s friend should not act rashly, for example, must not bake the headlights. If the operation is improper, this can easily damage the headlights.
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In addition to changes in weather, human factors can also make car lights "tear eyes", such as wading and washing cars. When the vehicle is wading, because the engine and exhaust system itself are relatively large heat sources, rainwater will form a large amount of water vapor on it. Along the vent pipe, part of the water vapor will enter the headlight.
Car washing is even more straightforward. Some car owners like to flush the engine compartment with a high-pressure water gun. After flushing, the accumulated water in the engine compartment was not treated in time. After closing the engine compartment cover, the water vapor could not be quickly dissipated outside the car, and the water vapor stuffed in the engine compartment might enter the headlights.