Condensation in headlights – a disadvantage of modern LED technology?

Condensation in headlights – a disadvantage of modern LED technology?

published on 11. February 2021

Visible water behind the lens? Steam in the housing?

Everyone has seen water or steam in headligh housings. The logical assumption is that the light is simply leaking and therefore defective. But this is not necessarily the right explanation, because even high-quality lights with a high structural tightness can show this effect. Especially with modern LED headlights, this seems to occur more frequently.

But is this really the case? And does this automatically mean that there is damage? To answer these questions, we need to take a closer look at a few aspects of this phenomenon.

Steam or small drops of water indicate condensation.

Even the highest sealing allows replacement

Well, for that you should first know that even headlights sealed to the highest standard are not hermetically sealed. The highest sealing class IP69K merely means that water cannot get into the light even under high pressure, such as during cleaning with a high-pressure or steam cleaner.

However, there are two things to keep in mind. Firstly, headlights are not produced under air seal, so even in a sealed housing there is always air. And air always contains water vapour, sometimes more, sometimes less, depending on temperature and region. Secondly, even in sealed housings there is an exchange with the atmosphere over the long term. Most headlights even have very small vents in their housing for this very purpose, but they are sealed with Goretex© membranes, for example, to be armed against high-pressure and steam cleaners. A slow exchange of gases will nevertheless take place over time.

Only very clear accumulations of water indicate a leak.

Even sealed headlights “breathe”!

Another aspect is that the inner workings (lenses, covers, etc.) and also the lenses of modern headlights are increasingly made of plastics. However, plastics are always hygroscopic. This means that these materials can and do absorb and release water from the environment. In short, they breathe.

And if you now also consider that water vapor has the property of condensing in cool places, you are very close to explaining the visible water. The coolest part of a headlamp is usually the front lens facing the surroundings. So it is not surprising that condensation water can be found there from time to time. And this is the case in every headlight, whether LED, xenon or halogen. But the question is why this seems to occur more frequently in LED headlights.

The disadvantage of good energy efficiency

There is a relatively obvious answer here. Headlights with conventional lighting technology (halogen or xenon) work significantly less efficiently than modern LED headlights. This means that a relatively large proportion of the energy absorbed is not released as light but as heat. This heat is mainly radiated directly to the front, i.e. onto and through the front lens. This means that it heats up and prevents condensation during operation. After switching off, however, clearly visible condensation can often appear in conventional lights as well. Just not during operation, when you notice it.

The good energy efficiency of modern LED headlights therefore actually seems to be a disadvantage here during operation, as less energy is “wasted” and radiated as heat. In direct comparison, the front lenses of LED headlights remain significantly cooler than those of halogen or xenon headlights, so condensation can be observed more frequently. But it is only observed, it is still not more frequent.

Condensation is usually only an aesthetic problem

As a rule, however, condensation on the inside of a headlamp is only an aesthetic problem. The visible amount of water or vapour does not usually lead to a reduction in performance or failure of the headlamp. Modern LED headlamps, however, offer such clear advantages in terms of efficiency, durability and robustness that these outweigh this small aesthetic disadvantage many times over.

But does this now mean that we have to live with it?

No, not necessarily. Today, there are already various approaches to preventing condensation even in cool LED headlamps. One obvious idea is to heat the front lens directly. But this would in turn lead to a deterioration in energy efficiency and thus represent a step backwards. So most manufacturers are taking other approaches. One is to use a cooling fan that directs the warm exhaust air from the LEDs over the front lens. This approach is currently preferred especially in the automotive industry. Another alternative is to apply an anti-fog coating to the inner front lens surface. However, such a coating does not eliminate condensation, but merely hides it. There is still some development potential here, which manufacturers are currently working on.


In a nutshell, condensation in headlights does not indicate damage. Even in sealed headlamps, there is a residual amount of moisture due to the normal air humidity during production. In addition, even completely sealed housings “breathe”, so that an exchange with the outside air continues to take place over time, albeit at a slower rate.

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