You might want to do more involved googling "research" and find http://www.bikequarterly.com/images/...Resistance.pdf. Among other things, it shows good dynohubs have less than 1 W draw when not running the lights. Google a bit more and you'll likely find that good dynohubs have less rolling resistance, with the lights off, than not-so-good hubs. I.e., there's no practical downside to rolling resistance from a dynohub.