I don't know, you guys. I rode for three months a 15km stretch of mostly pitch-black MUP, at top speed, with one 10W halogen on a helmet mount (http://www.blt-lights.com/gammaraysl42.htm). I paid $40 USD for it, and the old school battery was pretty heavy, but it was plenty of light, enough to bring out every bug out for miles around, with the hungry bats not far behind! (see bat story in very long commute thread).