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Can Heat Cycles Cause an Underwater Light to Draw in Water?

We have to admit, this was a new one for us. It’s one hell of a theory, and we can see how someone might have gone down this rabbit hole, but ultimately, it’s not true. 

We've been asked, as an underwater light goes through repeated heating and cooling cycles, can it cause an underwater light to "pump" water into the fixture over time.

The short answer is no. The light doesn’t suck in air. 

This query was so left field though, we thought we’d better write a short Knowledge Base article to debunk the myth.

As an example, let’s look at the X-Series X4. 

First, let’s talk design…

Our X-Series X4 is designed to be installed with the fixture fully sealed to the hull using 4200 marine sealant. Once installed correctly, the back of the light is isolated from the surrounding water.

While the air inside the fixture will naturally expand and contract in microscopic amounts as temperatures change, there is no external path for water to be drawn into the light. Without a route for water to enter, thermal cycling alone cannot cause the fixture to pump water into the light.

It’s also worth noting the temperature variations needed to achieve thermal cycling are massive. The variance of temperature of our underwater lights is far too small for a pump like reaction. 

So, onto the obvious question, why does water ingress occur?

We can’t speak to other manufacturers, but If water is found inside any of our underwater lights, it indicates that the sealing system has been compromised. Most commonly this is down to:

  1. Incorrect installation, a lack of sealant is probably the most common culprit here.

  2. Physical damage to the fixture, commonly the use of something like ‘LightSpeed’.

  3. Damage caused during cleaning. DON’T Jet wash lights! Follow our very simple cleaning instructions. 

As you can see, these situations are not caused by normal thermal expansion and contraction.

The Bottom Line

When one of our underwater lights is installed exactly as specified in the installation instructions, the fixture forms a sealed system. Under these conditions, normal operating temperature changes do not create a mechanism for water to be drawn into the light.