The upstairs bathroom got too much water on the floor and it dripped through to the kitchen below, by the ceiling light fixture (discoloration on ceiling around light fixture). The place was built about 7 years ago, with circuit breakers. Is there a fire risk having the lights on? Is there a fire risk keeping the lights off until it dries out?
Chances are the ceiling is damp and you'll be fine. However, I have never been a fan of water and electricity at the same time. With the breaker switched off, take the globe, glass off the fixture. Water probably wouldn't be in the junction box but could have dripped between the box and the ceiling. If there is any dampness, dry everything off. Put the fixture back together and operate the light as usual... the heat will dry out the ceiling.
Water can corrode connections, which increases contact resistance. When current flows in such a connection with high resistance, it will heat. This can cause problems. Water can also cause current to leak to Earth via the fixture or conduit metal parts and trip the RCD if you have one. If you don't have one, or if everything is not properly earthed, then some metal parts may be dangerous to touch. If you change a lightbulb you might get shocked. You probably won't be electrocuted that badly, but the most likely cause of injury is falling off the ladder due to the shock.
If the light fixture uses an electronic transformer, LED driver or LED lightbulbs and that gets wet, I don't think it can cause a fire but it can certainly damage the electronics if they are powered when wet.
After fixing the leak, you should check inside your light fixture for corrosion (turn off power at the panel first). Don't turn it back on until everything is dry.
I cant think of any non-obscure scenarios where water in a regular electrical installation could cause a fire. However it could cause some building parts to carry an electrical potential and current which means a risk of electrical shock, but even that is quite unlikely in the scenario you are describing. The most likely thing to happen is nothing at all. The second most likely thing is that either an RCD (aka GFCI) or circuit breaker will trip.
If the bathroom floor is not properly grounded there is a small risk of electrical shock if someone walks bare foot on the floor, and touches something grounded, e.g. tap or a radiator. But I consider it unlikely that the bathroom is constructed in such a way that the floor is not electrically bonded with all other metal parts (tap, etc). And even if so, I also consider it unlikely that the water could cause a fault current in the scenario you describe. Not impossible though.
I would not worry if I was you.
When the water has dried out, the danger is over. Until then you could consider wearing slippers in the bathroom and avoid showering.
Ours will splash outside of the tub, or hit it just right, so it runs under/around the tub onto the floor and then into the drywall ceiling. Enough water and it'll leak through the seams/follow them to the light fixture, and then fill up the light.
No, it's not going to break that much UNLESS you're taking baths in pure Epsom salts or NaCl. However it's a good idea to get those leaks fixed, or at least find out where it's coming from.
A one-off isn't going to be too bad. Just get some air into the area the leak was (access panel under the tub) and blow it dry.