Underwater swimming pool light fixture needs replaced

There are quite a lot of swimming pools with standard incandescent lighting under the surface of the water. The vast majority of them are either 300 or 500 watts and are intended to be submerged throughout their lifetime. We sometimes have a hard time explaining when it is time to replace just the bulb or the entire fixture. It can be easy to determine if there is water visible inside the fixture, but it is not always obvious when the light just stops working. Eventually, all underwater light fixtures will need to be replaced, because the swimming pool water deteriorates the rubber piece that seals the cord entry into the 'can' and/or the lens gasket seals. We can replace the bulbs several times, before the fixture will need replacement, as long as we install a new lens gasket each and every time we open up a fixture. However, it is not possible to be precise in determining how long a fixture will last (regardless of how many times the bulb and gasket have been done) because we can't replace the cord entry rubber seal. Generally, I see light fixtures last between about 10 - 15 years, but conditions vary so much that replacement intervals will differ greatly.

These light fixtures come from the manufacturer as a "sealed unit", meaning the power cord has been installed permanently and cannot be repaired - at all. So, once water gets inside a fixture, and it can be determined that it got in through the cord entry, and not the lens gasket, we have no responsible choice but to replace the entire unit. My experience has found close to a ~75% of lights with water inside need to be completely replaced, though I am tempted to replace them all, just to eliminate the return calls. A small number of them can be dried out and have a new bulb and lens gasket installed without any new issues for several years. These are usually the ones which have let water in through the lens gasket and not the cord entry seal.

Here I'm showing an example of one fixture that may have been a borderline replacement decision when someone tried to repair the seal at the cord entry point with epoxy. It looked very clean inside until I inspected the socket that the bulb screws into. I recommended a new fixture due to the obvious history of repair attempts. I didn't take any pictures of the lens and gasket, just the fixture.

Above is a good view of the fixture and its face ring. You can see the coiled wire loop, coming up from the back of the 'can' on each side of the socket, that is part of the grounding system. This wire is meant to touch the glass of the bulb creating a ground to it, since glass is a conductor of electricity - though not a very good one. There is a faint showing of rust on the lower right quarter of he can indicating that the socket is getting slightly wet and corroding.

Above, closer in, we see the temperature sensor (at bottom right - looks like a cigarette but) which will cut power to the bulb if it gets too hot. The red-orange gel surrounding the socket, ground wire and temp. sensor is the epoxy used by the manufacturer to protect each of these pieces from water and hold them in place for proper lighting function. We do see some moisture here, which has caused our problem, but it isn't enough to be seen from the waters edge, through the lens. The corrosion in the socket is much more obvious here and confirms the need for replacement.

A much better view of the corrosion. If we are trying to be fast and save some money, we would be tempted to clean this up with some sand paper, dry it out and put it back together. It may work for a while, but I would count on being back to replace the fixture soon.

When I see this, I know that someone was aware of the water getting in and may have thought it was not significant enough to replace the entire fixture. Instead, in an attempt to extend its life, they tried to epoxy the cord entry.  There are very few epoxies that are good enough to permanently stick to (and seal) both rubber and stainless steel. I have never seen this work (and my opinion is that it's a waste of time and money). Although, I understand that some customers want to do anything to save money, this is one I strongly recommend against because it can be a potential safety hazard (even with all the safety precautions in place).

Most lights show much more obvious signs of damage due to water getting in through the cord entry seal. I wanted to show this one because it seems to have fooled someone before me and I really want to help explain my idea of across-the-board replacement when possible.