I might add: make sure that you get LED lamps if using a dynamo hub...my wife and I (me in the function of replacing the bulbs) made the experience that common bulbs were regulary burnt out with the Shimano hub on the Kettler city bike she uses for commuting. Replaced the headlamp with a Basta Sprint Steady Switch for around 13€ - now burnt out bulbs are no issue anymore, plus she is enjoying a way more brighter light.

Shimano also offers some kind of external regulator/protector for dyno hubs, but since nearly all LED headlamps features an inbuilt overload protection, why spending extra money?