Under the 1968 International Vienna Convention on Road Traffic of the United Nations, a bicycle is a vehicle and like any vehicle, it needs lights at night. Here in the U.S., the Consumer Product Safety Commission (CPSC) has issued a warning to bike riders to take necessary steps to make themselves and their bicycles more visible after dark: "Be sure your bike has reflectors required on all new bicycles by the CPSC bicycle regulation. Each bike should have front and rear reflectors, pedal reflectors, and side rim or wheel reflectors. Use front and rear lights (as required in many States) to help make your bicycle more noticeable to cars at night. Small battery-operated lamps strapped to your legs also help."
Although these laws and warnings are in place and studies have found a clear correlation between bicycle lights and nighttime riding safety, it is believed that 75% of bicycles used at night in the U.S. do not meet the legal requirements for lighting. If you're not in that prudent 25%, the time is now to equip your bike with night lights.Some Green Bike Light Options (courtesy of TreeHugger):