Its not the pedestrians you need to worry about on the sidewalks, its' the cars pulling into or out of driveways. They are not expecting a bike moving on the sidewalk nor should they. That last time I looked into the stats you are about twice as likely to get creamed on a sidewalk as out in the road. If you are going to keep riding on sidewalks you need something better then 4 or 5 watts. A 20 watt halogen or better please. Or two lights at 10 watts each, one tight beam to light the walk and one floodlight to warn the drivers. Aside from lights, truly, consider taking the LAB (League of American Bicyclists) effective cycling course.