I have one of these ...
Whoops, the light fitting is in fact the 240v model:
when off'.
There is a very small capacitance formed between the wires of cables. This capacitance, lets the AC voltage 'leak' through between wires, and induce a small current. It's utterly harmless (unless the cables are kilometers long), and pretty much happens because current design practices for house wiring were designed for filliment bulbs, where this level of current causes them to warm to a couple of C over ambient. With many sorts of energy saving light, this can instead produce very small amounts of light, instead.
The amount of light needed to be visible in a dark room is very, very small. A normal LED torch runs at 20 thousandths of an amp. At a millionth of an amp, it's clearly visible in a dark room.
Thanks Ian, I can shower with confidence again!
Another thing to check that can make this effect more prononunced is if the switch is in the neutral rather than the live...
And also those light switches that have an indicator that comes on when the main light is off to show you where the switch is. These rely on a small leakage current through the bulb to light the neon and are only suitable for filament bulbs.
Christian.
Actually, we have one of those for the hall light. The switch in question is just inside the front door, and it's a useful place to have an illuminated switch.
But there are no filament bulbs on the circuit - just two CFLs (OK, in parallel, of course) and there seems to be enough leakage to make it work.
It's rarely lack of leakage to operate the indicator that is the problem. It is more the effect this leakage has on the lamp. A filament lamp will stay dark. A CFL or LED could do one of many things, including staying dark, lighting very dimly or flashing. It depends on the design of the individual lamp.
Christian.
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