How excactly can you fire the candle? With what object?
Just move the cursor over it and when "Candle" pops up, left click on it. Hey presto, let there be light. And a funny undead dude following you about.
My one problem with him was that once I'd got him, I didn't want to go back to the surface until I'd got all the use I could out of him (i.e. he was dead. Again). So I spent ages trawling around the lower reaches of that place burning potions and snack food in a desperate attempt to avoid Aleroth. Still, he helped me out in a couple of tough fights, so I reckon it was worth it.