Dynamo basics, and not so basics here:
Bicycle Dynamos

Some circuits here
Dynamo LED Light Systems for Bicycles (electronic circuits)
There has been a small drop in LED Vf since Martin did these charts so equivalent speeds will be a bit less.

Summary:
Will deliver 500mA into an LED, or string of LEDs. You need to go faster to make more LEDs light up.
Without some smoothing the LEDs will blink annoyingly.