I have two LED lamps in my corridor, and when I switch them off, they keep emitting light (not very strong, but it's annoying at night).
What can it be? How can I fix it?
Some light switches run a small amount of current through the bulbs even when off, usually to power small devices at the switch like a timer, motion sensor, or night light. Do your switches have either of those features, or something else like that?
The way those devices work is instead of having a hot/neutral pair powering the switch, they just sit inline with the hot wire and draw a very small amount of power. Old fashioned incandescent bulbs won't light up if there's only a small amount of electricity running through them, so you would never notice this current, but LEDs are much more efficient and apparently are getting enough power to run.
If that is the cause of the problem, there are a few solutions:
If we're talking a high voltage circuit, w high intensity LEDs: Many high intensity white LED's use a phosphor that is in fact phosphorescent, like glow in the dark paint. You just have to wait for it to dim down. Switching to a different brand of bulb, with a different phosphor may help, but it's hard to "try before you buy".
If we're talking a low voltage circuit, 5-12v: A capacitor in line with an LED can power it for quite some time. You can limit this effect by by using a power supply with a smaller filter capacitor.
If the light is controlled by 3-way switches wired with a 3 wire conductor, the electromagnetic field will induce enough voltage on the other wire to dimly light an LED bulb.