I was mystified by something I experienced today. I'm sure any
electrician will know the answer. Sorry if its a naive question.

I was using one of those electrical screwdrivers with abuilt-in diode
for identifying live wires. I wanted to disconnect a security light on
my house but I wasn't sure which circuit it was connected to. I
concluded the light was wired into the lighting circuit, because it
failed to come on after I pulled the main fuse from that circuit. But
just to play safe, I touched the screwdriver onto the terminals in the
junction box which the light was connected to. The diode didn't light
up. However, when I touched the brass end of the screwdriver's handle,
it lit up, quite brightly. So I found my volt meter and tested the
wires to see if there was any voltage there. No voltage registered.
Can anyone explain why the diode lit up when I touched the brass end?
And it lit up the same, whether I touched the screwdriver onto the
live, the neutral or the earth terminal.

Regards,

Drake