In reply to TeaGirl:
SPeak to your local friendy mountain biker who night rides. IMO MTB lights are at the forefront of portable light technology. Used to be halogen, then HID and now it's LED.
I use my now old fashioned 4 years old lumicycle bike lights cabletied to my petzl headtorch headband with a piece of board to act as a heat sink for night stages in adventure races. Trust me. MTB lights are the way to go. For 12 hours un time form a sensible sized battery you need either HID or LED. LED will be best as a headtorch due to heat issues.
USE exposure joystick? all in one unit.