Outdoor Lights Not Working After Rain? Here Is What Is Usually Wrong

It is a familiar one. The garden lights were grand all summer, we get a proper wet week, and now half of them are dead. Or worse, the whole downstairs trips every time you flick the switch for them.

Dublin gives outdoor fittings plenty of chances to fail. Met Éireann recorded 184 rain days at Dublin Airport in 2025, 134 of which were wet days, meaning a millimetre of rain or more, with 804.2 mm of rain over the year. An outdoor fitting here is not dealing with the odd shower. It is getting soaked, drying, and getting soaked again, a few hundred times a year.

Why does rain stop an outdoor light working?

Water does not have to fill a fitting to stop it. It only has to get far enough in to make a path between a live part and earth. Once it does, one of two things happens.

Either the moisture corrodes the connection until the circuit is simply broken, and the light goes dead on its own, or the water bridges live and earth, current leaks where it should not, and the RCD in your board does exactly what it is designed to do and cuts the power. That is why a garden light fault so often takes out the sockets or the lights inside the house at the same time. People assume the two are unrelated. They are usually the same fault.

The common ways water gets in are worth knowing, because they tell you where to look:

• the seal or gasket around the glass has hardened and stopped sealing
• the cable gland underneath was never tightened properly, so water runs down the cable and straight in
• the fitting is mounted facing upwards, which no outdoor fitting enjoys
• a junction box behind the fitting is indoor grade, or is sitting in long grass
• condensation, which forms inside a sealed fitting as it heats and cools, and has nowhere to go

What does the IP rating on a fitting actually mean?

Every outdoor fitting carries an IP rating, two digits after the letters IP. The first digit is about solid things getting in, dust and the like. The second is the one that matters outdoors, because it is about water.

IP44 means splashing water from any direction. IP65 means it will take a low pressure jet. IP67 means it can be temporarily submerged. A fitting sold as suitable for outdoors is not automatically suitable for your outdoors. A light under a deep porch that never sees direct rain is a different job to a light on an exposed gable wall or one set into a step where water pools around it.

We see a lot of decent quality fittings failing early simply because they were the wrong rating for where they ended up, or because the right fitting was installed with the gland left loose. When we do garden and outdoor lighting we pick the rating for the position, not for the catalogue photo.

Why did it start working again by itself?

This is the part that costs people money. The light dries out over a few clear days, the leak path disappears, the RCD stops tripping, and everything seems fine. Nothing has been fixed. The water still has a way in, the corrosion is still spreading, and the fault comes back with the next wet spell, usually worse.

An intermittent fault is still a fault. It is also the hardest kind to find later, because by the time somebody is looking at it, it is behaving itself. If you know roughly when it started and what the weather was doing, say so. It genuinely narrows things down.

What can you check yourself before ringing anyone?

Only the safe, obvious things, and only with the circuit switched off at the board:

• Has the bulb gone? Swap it for a known good one. It is the cheapest test there is.
• Is there visible water sitting inside the glass or the diffuser?
• Is the fitting loose on the wall, or is the seal perished and cracked?
• Has anything been added lately, a new socket, a pond pump, a hot tub, that started around the same time as the trouble?

What not to do is keep resetting a tripping RCD to get the lights back on. It is not a nuisance switch, it is the thing standing between a wet fault and somebody getting a shock in their own garden. The CRU and ESB Networks advise testing your RCD twice a year, when the clocks change, by pressing the test button. If it does not trip when you press it, that is a separate and more urgent problem.

Beyond that it is a job for a meter rather than a guess, which is most of what fault finding is. Isolating which fitting is leaking on a run of five or six means testing them, not eyeballing them.

Worth sorting before the winter

Outdoor lighting gets used hardest between October and February, which is exactly when it is wettest and when a dark path or driveway matters most. A fault found in September is a straightforward job. The same fault found in December, in the rain, with the power tripping every evening, is a miserable one.