Generate current and power LEDS off a bike wheel
Buy a standard bicycle dynamo like this one.



You need some form of regulator. However, you should probably use a current limiter rather than a voltage regulator. The LEDS will be dim when you are moving slowly, but that would be preferable to just dropping out.

If it is for navigation/warning lights I would also add a battery to keep the lights on when you slow down or stop though. 

By the way. I would NOT use a buck regulator for this application. Dynamos make a lot of drag on the wheel, so you really don't want to try sucking amps out of it when you are not moving very fast.







simulate this circuit &ndash; Schematic created using CircuitLab