Some people may want to run two front or rear dynamo lights, or even two front and two back at the same time!
Is this possible, technically yes however what you would generally find is that with two front lights (front lights drawing the most power) is that you wont achieve much/ any increase in brightness unless travelling at very high speed.
We advise people don’t add more than one front and one rear light, due to the unnecessary load it hubs the hub under. In some cases we have seen two rear lights used, which I believe is acceptable as they consume very little power. The same cannot be said for front lights however.
Note from SON website:
Is it possible to run 2 Edelux II on one hub dynamo?
In contrast to headlights with bulbs, it doesn‘t make sense to run 2 Edelux II on a hub dynamo in general. You may connect 2 headlights in series, but only at very high speed there will be significantly more light.

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