B&M Lyt N is pretty low cost ..

I have used Halogen bulbs in DIY battery pack lights and they work OK .. but with a dynamo you need the total load=to the dynamo output
So headlight only it needs a 3w bulb ... add a wired taillight, 0.6w and the headlight is 2.4w.


a battery will have the draw determine the need , and I got away with a cheap halogen flashlight bulb
rated higher wattage than I was supplying . 5 1,2v D cells in series .