measure RMS power from bicycle induction light

this is my first forum post, so please pardon me if it's not in the right place etc.

I would like to know what kind of power output you get from a small induction circuit on bicycles, like these:
Reelight: Magnet Powered LED Bike Light | Gadget Lab | Wired.com


I have access to most basic lab equipment.

I have considered the basic just measuring voltage over a known resistor and monitoring with a scope. Seeing how much one turn on the wheel gets, i can calculate power output as a function revs/min i guess?


maybe it is better to see, how much a known capacitor will be charged over time?

something i have overlooked?

It probably would be easiest to let it charge a large capacitor (large enough so there is no significant ripple under load), add a known resistive load, and measure the voltage. Then power = V²/Rload. You could try different loads to see which produces the most power.