The cost of using a 100-watt light bulb for 24 hours is 21 cents, whereas a compact fluorescent light costs 4 cents for 24 hours, according to an example from the city of Thief River Falls. These figures assume a cost of 10 cents per kilowatt-hour for electricity.
With over 50,000 hours of usage, a 60-watt incandescent bulb costs $300 in power at 10 cents per kilowatt-hour. A CFL uses $70.83 worth of power over the same span and an LED light costs $39.58, according to Energy Use Calculator. Energy Star's calculating tool determines how much power certain light bulbs cost to keep lit.