Running multiple dynamo lights on a single dynohub
Most bike dynamos produce roughly constant current, so if you ride fast enough, doubling the resistance by wiring two lights in series gives 12v, neatly split between the lights. The classic setup in old days was two lights in series and switch to short circuit one when riding slowly, so that the other would get the full voltage.
Some new LED lights designed for dynamo can take advantage of this feature even with single light, so it would make sense to not add any current limiting to new models. The only way to know if it works for any specific model is to try.