Originally Posted by
steelbikeguy
...
The dynamo's open-circuit voltage is essentially proportional to the speed, which does present a challenge when trying to deliver a constant power to something as delicate as an incandescent bulb.
This is accomplished by the design of the dynamo and the selection of the bulb's resistance....
Years ago on a sidewall alternator with incandescent bulb I wired in a couple zener diodes to trim off the voltage peaks when I went down hills. I think I used 8 volt diodes.