Originally Posted by
noglider
Wouldn't that be too high power for the dynamo? Dynamos typically are rated at 3W, no?
You don't need to run the LED at full power (the resistor in the circuit limits the power draw), and no dynamos aren't rated at 3W, 3W is what they deliver when hooked up to the traditional incandescent bulb.
Bubbles; DX product descriptions are usually screwy. Pretty sure thats a cree XPE, Vf ~ 2.3V and max current 700mA. Yes, heatsinking is a good idea but at 150mA you might get away without it. At least move the resistor out of the case.
OP, You probably want to use two of those LEDs (will better match the 6V from the light). You can get a board with 3 on them from cutter.com.au. Not sure why Supernova say not to use another tail light, there are plenty out there... Maybe a too high power draw will kill the headlight? Have you emailed them to ask and pointed out your reasons?