Condensation happens when the outside of the lens is cooler than inside the lens. When you drive around with lights on for a few hours, the bulbs warm the air inside the headlight lens. The same thing could happen when the headlights sit out in the sun all day.
So now the air inside the headlights is warm. If you turn your lights off or pull your vehicle into the shade, there will be a large temperature difference between outside and inside the lens. The cool air wants inside and it begins to sneak into the tiny vents that are found on most headlights. When that cool air meets with the warm, condensation is formed. That happens on the warm side of the lens, so you have got a little layer of moisture on the inside of the headlight lens.
Condensation
Condensation is the change of water from a gaseous form (vapor) into liquid water. It appears as small droplets of moisture inside the light.
Condensation does not cause a problem with normal operation of the light and is, therefore, NOT considered to be a defect or warrantable condition.
In fact, ROADSIDE lights are designed to allow moisture to escape and not reenter, but it takes time for the moisture to evaporate (the amount of time will depend upon whether or not the light is turned on or not).
