Looks like the dynamo type lights take 6v AC. Does anyone know if they can take DC? Some appear to have a capacitor for continued lighting when stopped for a period of time. That seems to imply that they would at some point rectify the AC and charge the cap with DC, which would in turn power the light off the same DC?
I use a 12v system for various other things so in thinking through this - it would be conceivable to make a converter from 12v to 6v, but it would be DC. I don't think it is worth trying to add an oscillator to create a frequency from which to drive an "inverter" that could replicate 6v AC.