It's about putting enough candlepower out there to identify and avoid the walkers, runners, and other cyclists out there with no light, no reflectors, and dressed out in solid black (or sometimes camouflage, this being the Deep South). I call it "ninja-detection mode." Our trails aren't consistently lighted, and in addition to the ninjas, there's quite a bit of wildlife, ranging from deer to possums, armadillos, and skunks to watch out for. Hit one of those latter critters in the dark, and you'll be a believer in bright lights, too.

State law requires me to run head and tail lights when I'm out riding around in the hours of darkness. In the lighted sections of road and/or trail I'll usually run in flashing mode in order to save battery power. When it gets into the dark (and wooded, twisty) sections, I switch to steady beam for better visibility.