I'm in Chapter three and am helpingt he Wandering Village (IIRC) the one with Nym in. I have got the ghosty guy in the forest and he asked me to kill all the lights. The thing is when I enter an area where there is one - it disappears and I have to follow it and kill it.

But how many are there?

Recently I got about three and they all disappeared and I couldn't find them again. Does anyone know how many there are?

When the ghost gave you that quest to get rid of the "lights", he does not mean those you see on the way. You have to get to the Inner part of the woods.
:)
Basically, you use the wilderness lore to get back to the same place where you found the horn, then from there, use the lore again to find the inner woods. i think you have to exit at the top right of the horn-map first, or maybe the bottom right. :D

This question was asked before, you can search the forum for it.

Thanks -_-

There are abot 3 will o the wisps.
You will also need to kill some treants.

Cheers.