Nah, I'm only using a resistor to limit current. It was tricky to get the right one in there too, since it didn't seem to follow ohm's law... or at least, the diode voltage drop was different than what I had calculated. In any case, I blew out two LEDs (the original chinese knockoffs that were in these flashlights) so I had to replace them with genuine Luxeon LEDs... It's probably better this way anyway, at least the LEDs are the same colour.

I still may add some ground FX LEDs as well, since as you can see from the night shot the bike isn't very visible except on the front and back.

Hmmm, buck current regulator, eh? I went the resistor route for simplicity's sake (it had to fit inside the body of one of the lights), but if I can find a clever way of properly regulating current, then I may do so.