Compact fluorescent bulbs are much more efficient at producing light than are ordinary incandescent bulbs. They initially cost much more, but last far longer and use much less electricity. According to one study of these bulbs, a compact bulb that produces as much light as a 100 W incandescent bulb uses only 23.0 W of power. The compact bulb lasts 10000 hours, on the average, and costs $ 12.00, whereas the incandescent bulb costs only $ 0.76, but lasts just 750 hours. The study assumed that electricity cost $ 0.090 per kilowatt-hour and that the bulbs were on for 4.0 h per day.