Bike lights have two purposes: to see where you are going and to be seen by others. There is a misconception that if you ride a bike in the city you do not need bright lights because there is ambient lighting from street and car lights which allows you to see and be seen. While any small powered bike light is better than nothing, a bright light will improve your safety by extending your ability to be seen from a greater distant and providing better illumination of the road.
Earth Rider Blog about Cycing
Sharon Kaminecki and others comment on adventures in bicycling and other stories