Was over at someones house yesterday and they have deleloped a very strange fault with a light.

Problem is.

40W non energy efficent bulb works fine.

various W energy bulbs have strange faults. One would illumuinate very slightly when turned off. Another would flicker when off.

Both work fine when the light is turned on.

When off there is 2v ac at the lamp holder with no bulb. When a 10W long life bulb is put in the light flickers and the voltage jumps to 90V ac peaking at about 114V ac.

Any ideas?.

I think that there is an arch on the lamp holder to cause the flicker or a faulty earth. But there shouldn't be any voltage to the holder as the switch is off.

Faulty switch?

Damaged cable?

I think you have a neutral fault or a faulty switch.

It is possible for AC to "back voltage" when there is a loose conection somewhere on the circuit. The problem is often tricly to trace as you need to systi,aticly go through each place there is a joint or connection and check all is tight

I would also say a faulty switch