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Prevent Moisture from Light Fixture

Prevent Moisture from Light Fixture

Prevent Moisture from Light Fixture

Hi Guys,

I have a cylindrical-shaped outdoor light fixture. Imagine sealed Dia 8in x 30in tall clear cylinder. light source at the top end.

The fixture is sealed well and is water-resistant. Still, periodically, I observe a moisture patch on the inside closer to the bottom part of the cylinder. Is there a way we can prevent this from happening?



RE: Prevent Moisture from Light Fixture

Water-resistant is not the same as "sealed"... what you're likely seeing is moisture in the internal air condensing out to water droplets. The only way to prevent it is a sealed container that has been flushed of moisture (like a nitrogen purge).

Dan - Owner

RE: Prevent Moisture from Light Fixture

Over time as it heats and cools the air expands and contracts. When it cools and contracts it will draw in moist outside air. When it builds up enough you will get condensation.
A dry nitrogen purge would slow the process down.
I have also seen fixtures where there was an internal cavity in the top of the fixture to hold a desiccant package. this can often give you a year of moisture free operation combined with good sealing.

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RE: Prevent Moisture from Light Fixture

Your solution can be found here:


Vents utilizing Gore-Tex technology can prevent water from entering the fixture while also allowing water vapor in the fixture to escape.

RE: Prevent Moisture from Light Fixture

You might actually be better off venting the cylindrical fixture top and bottom so you get some air movement in and out of the can. You want a drain hole at the bottom, and of course, you can’t plant it in water. You want it to shed/resist taking on any water in a rain storm, but it is very difficult to stop it from breathing during the hot and cold cycling as EdStainless suggests. The top vents should be under the top lid and its drip edge. The bottom vents should also be shielded in some way, against driven rain, and a few inches above grade.

RE: Prevent Moisture from Light Fixture


I am glad I shared my concern here. Thanks so much for sharing various ideas. Can't wait to try them.

Thanks again


RE: Prevent Moisture from Light Fixture

Semi-closed enclosures are extremely efficient water pumps; we had an 18-in diameter spheroidal enclosure that could, in a matter of days, accumulate a inch of standing water. Unless your enclosure is hermetic, it will pump water from the atmosphere; it is progressively worse in humid environments with cool nights.

TTFN (ta ta for now)
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RE: Prevent Moisture from Light Fixture

Let me be more direct with my link:


Gore has a solution for this problem. They have other options that work as well. We have thread mounted vents on our flood lights. Zero condensation after 3 years now.

RE: Prevent Moisture from Light Fixture


Quote (tugboateng)

Thanks a lot for this tip.

I would be curious to know if there is way to figure how many gore vents we should use. Or figure how many we need. I am sure there is a relation to volume.
I will check their website or check their tech support.



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