You can use a flashlight, lots of options with either a Zefal Doodad or Twofish Bikeblock for easy mounting..

http://www.amazon.com/Zefal-Doodad-P.../dp/B000AO3FTE

http://www.amazon.com/gp/product/B00...7HK8DVDRZ7T7T6

If you use 18650 cells, this light is a nice one.. 300 lumens, long burn time of 3+ hours in high mode.

http://www.shiningbeam.com/servlet/t...4-II-NW/Detail

If you prefer using aaa cells with options for longer runtimes in the future, this is a good light, Romisen RC-C8 II R2 Flood-to-Throw LED Flashlight. You can adjust the beam to your liking, either tight for long throw or opened wide for full flood.. 200+ lumens.. 3.5 ounces, 5 ounces with battery..

http://www.shiningbeam.com/servlet/t...h-C8-II/Detail