http://www.google.com/search?q=hub+d...owerforums.com

There are soooo many thread to read.

My light is a two XP-G warm white leds wired in series in a square aluminum housing with a schotky bridge rectifier and a switch. For reflectors I use two reginas from ledil optics.
It is really simple and provides more than enough light for less than 20-30$
One day I will add a circuit that "senses" the frequency of the dynamo's output and when it is under a limit (when the lights start to flicker) it will switch to a backup battery. If you can read a datasheet and can make a pcb google LM2917.