Having spent most of last winter training in the dark I know a little about this.
To ride comfortably I found I needed a 15w narrow beam hologen. Wired this myself(with a 10 15 or 20 head depending on ride time) and works great although it needs a recharge every ride. Used it along with a 1w luxon led helmet mounted(6 hrs from 4AA batteries) so I could see what I was looking at as well as where I was going!. For my fiji tour I took the led light as it is small and light. I ended up needing it one day for 15min(it gets dark real fast in the tropics!). Its summer now so I dont bother with the hologens but will put them back on when winter comes.
Something like this is probably an ideal emergency and around the campsite light
http://peterwhitecycles.com/b&m.asp