Is Water in the Headlamp?
Photo Credit To Industrielblick/

Is Water in the Headlamp?

What to do and what not to do if condensation strikes.

Condensation in headlamps can be detected as a thin veil of humidity that has deposited itself on the inside surface of the headlamp lens. It occurs only during specific weather conditions, mostly when the vehicle is parked outside during a cold and humid night.

Humidity condensation

Humidity condensation occurs where warm and humid air comes in to contact with a cold surface; humidity, which is contained in the air, simply lays down on the surface. As such, headlamps can be particularly susceptible to this type of condensation.

Headlamps are water-tight products, which need to breathe via ventilations, so humidity can enter and exit the headlamp. This humidity may enter in contact and lay down on a cold portion of the surface. During a wet, cold day, with an external temperature around 10 – 15°C and relative humidity above 85%, moisture condensation can take place in the interior of the headlamp.

Many people believe that condensation will only occur during winter conditions, but this is not true as it can occur all year round. When the temperature is high during the daytime and it drops overnight, this will cause conditions that can produce condensation inside headlamps.

“A high humidity level when the car is being washed may also lead to condensation in the headlamp.”

Why do headlamps “breathe”?

When the light is switched on, the heat coming from the bulb increases the air temperature inside the headlamp. In order to avoid a pressure increase inside, the headlamp needs to exchange air with the outside.

Specifically designed venting holes allow for the necessary air exchange, while protecting the headlamp against water ingress. After the bulb is switched off the internal air will cool down, and the headlamp “breathes” air from the environment. This incoming air could be humid and, if so, will eventually condensate at cold surfaces within the projector.

All headlamps are vulnerable to condensation, but how amplified this is depends on their environment inside the vehicle. On modern headlamps, which feature clear glass, the effect is more visible than on the older generations where stripes would often mask the appearance of condensation.

Consequences for the headlamp

Headlamps are designed as open systems, with a normal air exchange with the environment. Those that have spotted the effects of condensation could suspect there is actual damage to the headlamp. It is not, however, harmful to the headlamp as these components are designed to withstand such conditions.

Under normal circumstances, any condensation inside the headlamp should naturally disappear. Lighting system activation can also further accelerate the drying process because of heat generated by the lamp.


When condensation is present inside the headlamp it needs to be dried using the heat generated by the lamps. You should switch on the headlamp and wait for 30 minutes – under normal circumstances any condensation inside the headlamp should disappear. If you want to accelerate the process, you can open the caps (covers over the access to the lamps) for better air circulation, but don’t forget to put them back in place again after.

“Don’t be tempted to clean the engine compartment with a pressure washer as this generates a lot of humidity.”

After drying, the headlamp’s water protection characteristics must be checked. You should check that there are no cracks or damage at the front or the rear and that the glue sealing between the glass and housing is undamaged. Caps should be present and well placed and any ventilations should be in a good state and correctly fixed. Bulb sockets should also be correctly locked.

In the event that a significant quantity of water has entered the headlamp, it must be replaced. Water ingress can also be visually detected by water marks that remain on the glass or on the reflector.


Don’t be tempted to clean the engine compartment with a pressure washer as this generates a lot of humidity that might enter the headlamps. Some technicians have also been known to heat the headlamp lens with a heat gun, but the synthetic material is heat sensitive and may be damaged.

Don’t inject pressurised air into the headlamp, as this could project pollutants inside, while injecting warm and humid air into the headlamp could even amplify the effects of condensation. Lastly, you should never drill holes in the headlamp or try to dry the headlamp in an oven.

For further details about Valeo’s range of headlamps and bulbs, click here.

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