I used a CygoLite Rover II LED light that ran off a battery back. The top rating was 255 lumens, but I usually used it on the medium setting which was nearly as bright but lasted a long time, let's say maybe 220 lumens. I got a wheelset with a SON hub and in October I bought a Busch & Müller Lumotec IQ Fly (with standlight) which is now mounted on my primary commuter bike. It seems a bit dimmer than the CygoLite. It rates on a different scale, at 40 lux. There is no easy conversion between lux and lumens, but I would guess the generator light comes in at less than 200 lumens. Still more than adequate for lighting my way. The B&M lights are built to German lighing standards so there is a very clearly defined edge to the lighted area. There is a lit area that is more than bright enough, and just outside that, nothing. So the thing that took some getting used to is having a tunnel vision effect since there is not really any "halo" around the main beam. When it is in the standlight mode (i.e., when I stop), it stays lit, but dims to about half full brightness. Enough to be seen by traffic. As soon as I start rolling it comes back to full brightness. I feel no discernable drag due to the dyno when I'm riding.

The limitations on the dyno light in terms of smaller illuminated area are more than made up for by its benefits- not having to mess with charging a battery and unlimited lighting time.