Based on some tests performed on a common 6V-3W dynohub (Shimano DH-3D32) span at an equivalent of 20 km/h on a 28” wheel and connected to a variable resistive load, I plotted Power vs Load Resistance getting a maximum of power at about 30 Ohm load.
At this point I tried several filament lamp configurations aimed to get closer as much as possible to the above indicated optimal resistance.
In the WIRING DIAGRAM below all labelled powers and relevant resistances are the nominal ones whereas in the next table all reported numbers are actually measured values.
CONCLUSION: using a 3-ways single pole selector (S1) it seems to be possible to have the following lighting modes:
S-0 - OFF
S-1 - Common Head and Rear Light combination mode (normal mode)
S-2 - Reinforced double front light configuration mode (flood mode)
REMARK: as said above all tests have been performed with very common tungsten filament, it’d be interesting to repeat same test either with alogen filament lamps and led lights.