Re: Light powered by engine
if you wanted, you can get a single component cree HID led from superbrightleds.com and build one with advanced electrical knowledge. the problem is that the voltage can be anything in a reasonable range (2.5 - 36v) what matters is current, for leds its mA. these leds require at least 300mA and to provide awesome light, up to 800mA in some cases. this causes problems with the spark, killing the motor also.
i spent 80 bucks and bought a sturmey archer xl-fdd. its a 6v 3w dynamo built into the front hub. some people make quality lights for dynamos at a steep price, im building my own power station to charge a cell phone, my lights and a sla battery. not at the same time of course...
in all, if you just want to ride without worrying about battery charging... just go with a 30 dollar solar trickle charger. its 12v giving a larger range of lighting choice, its cheap, and its hands free. best of all, you get to keep 25% of your engines power.