There is compelling information about the increased visibility, safety, and common sense that comes with riding your bike ( or even in your car ) with the lights on. Pedestrians, car, truck, bus and light rail operators, other bicycle riders, all will see you better if your lights are on.
Increasingly the costs of lights come down, and the efficiency of LED lighting which has expanded to almost all new bike lighting, means that they have longer run time ( less battery cost ) and are more durable.
Did you know that in many places in the US that lights on a bicycle are mandatory?
Here is the State of Washington Revised Code pertaining to bicycle lights. I will bet that the code will be further revised in the next few years to make a rear light mandatory on bicycles as well.
RCW 46.61.780 Lamps and other equipment on bicycles. (1) Every bicycle when in use during the hours of darkness as defined in RCW 46.37.200 shall be equipped with a lamp on the front which shall emit a white light visible from a distance of at least five hundred feet to the front and with a red reflector on the rear of a type approved by the state patrol which shall be visible from all distances from one hundred feet to six hundred feet to the rear when directly in front of lawful lower beams of head lamps on a motor vehicle. A lamp emitting a red light visible from a distance of five hundred feet to the rear may be used in addition to the red reflector. (2) Every bicycle shall be equipped with a brake which will enable the operator to make the braked wheels skid on dry, level, clean pavement.