I use a bright light at night (CygoLite Rover II = 250 lumens max) so that I can be seen and see tealth bicyclists especially the ones on the sidewalk who drop down to the road at the most inconvenient tmes and do so without even glancing to see if something's approaching them. I also like to see potholes, ridges and other debris on the road as well as kitty cat size black critters with white stripes. One of the latter was startled by a friend of mine late one evening as he was riding home with a very low powere be seen light. He had a heck of a time getting tomato juice at that time of the night and a couple of stores even told him to leave. I'm very glad i wasn't with him that time.

Cheers