I don't have the Edelux, so this is just a guess, but perhaps the light isn't properly grounded. When you spin the tire by hand, maybe the frame is grounded because the frame is connected to the ground by whatever is holding up the frame (you or a frame stand). When you ride the bike, the frame is not grounded because the tires are insulating it from the ground. On the other hand, why would the frame need to be grounded? It is more likely that the light would need to be grounded to the frame. [Editing out my obvious wrong suggestion, so as to not mislead future readers. Between the dynohub and the light, there needs to be only two wires. The light does not need to be grounded to the frame, and the frame certainly does not need grounding to the earth.]
Could that ring be intended for grounding the light to the frame?
These are just some guesses.
- DaveS