Basic output of dynos in general: MOST bottle dynos are 6 volt 3 watt, there are some 12 volt out there but they are the exception. The old Sturmey-Archer GH-6 dyno puts out 6 volts 1.8 watts (give or take) the ones incorporated into the gear hubs ie; FG or AG put out a bit less. Modern dyno hubs put our either 6 volt 3 watt or 6 volt 2.4 watt. The 2.4 watt is for the EU market to meet some specific requirement. I have at least one of each of these models. Modern LED lights will work well with ALL of the dynos I have. I have not tried them with the 12 volt one, on that one I expect you would need to be careful that you did not over drive the LED and burn something up.

My most successful LED system is the one on my 1971 Raleigh Twenty. I used a 1970's AG hub, it would barely drive a 2.5 watt halogen head light. I converted to the B&M LED (Lumotec Cyo) it would drive that and a 4 LED tail light at a brisk walking pace. I have since swapped the head light out for the newer B&M Classic

Aaron