Follow-up on the UltraFire C3 Q5. With 2x AA NiMH, it's still bright enough, and it lasts at least long enough for my 42 minute commute.
I did have some problems with the switch though. It seems erratic. I went over a bunch of gravel road, fairly rough, with minimal problems, but then it just kicked into strobe mode while riding on smooth pavement. Also at several points the output level dropped down a bit, and went back up when I whacked it. So, power is OK, but the switch, not so much. The build quality on my sample is otherwise excellent, but if that switch doesn't mend itself (I've seen switches get better after a little use) it's going to be a problem.
I bought the flashlights as an experiment, and they seem to be a good solution weight-wise. But IMHO if I were going to spend $50 on a headlight solution, I'd go with DIY halogen again. When my HID bulb dies, I'm putting my MR16 fixture back on the bike and using the flashlight as a backup.
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Work: the 8 hours that separates bike rides.