Little attention has been directed toward the environmental and economic costs of light pollution. We estimate that 2.5 percent of the total United States electricity production is expended on nighttime outdoor lighting. About 30 percent of all outdoor nighttime lighting ends up in the night sky. This is equivalent to 17.4 billion kilowatt-hours of electricity, more than the individual electrical production of many countries, including Chile, Cuba, Hungary, Ireland, Indonesia, Israel, Libya, Peru, Syria, or Vietnam. About one half of light pollution arises from direct upward lighting and one half from reflections off the ground and buildings. Light pollution directly costs the country at least a billion dollars a year in unnecessary electricity charges, in addition to the associated environmental harm from the mining and burning of fossil fuels to generate this wasted electricity. The equivalent of 8.2 million tons of coal (or 30 million barrels of oil) are burned annually in the United States simply to light up the night sky. The proper use of full cut-off shielding, timers, and appropriate light levels, if widely instituted, could reduce the overall urban sky glow by at least a factor of four in the next few decades.