Use this CFL savings calculator to figure out how much money you can save by installing compact fluorescent lights to replace incandescent lights.
The calculator assumes an average incandescent bulb lifetime of 1,000 hours and an average compact fluorescent bulb lifetime of 8,000 hours. You can change this if you wish based on the advertised lifetime hours of either the original or replacement bulb, or both.
For LED house lights, see my LED savings calculator.
Remember that there are cases where replacing incandescent bulbs with CFLs does not make sense financially, or environmentally – cases where the light is so seldom used that the added expense of the new bulb doesn’t cover the savings. So as you change incandescent bulbs for CFLs in rooms where it does make sense, be sure to hold on to those old incandescents!
One of the conclusions you can draw after using this CFL savings calculator is that the push to eliminate incandescent light bulbs is perhaps ill advised. Yes, the incandescent light bulb is far less efficient than a CFL and produces far more heat than light. But there are many situations where the added expense of a CFL (and the added environmental disposal hassle, since CFLs, like all fluorescents, contain toxic mercury and must be disposed of through a hazardous waste dropoff) aren’t justified by the minimal savings. I have a narrow furnace room that is just big enough for the furnace, hot water tank, and a bit of storage. I need to turn on the light down there occasionally to look for a stored item or when the technician does my annual furnace maintenance. The light is on for about three hours a year at most. At 3 hours per year, that translates into 0.0082 hours per day, which at my current electricity rate saves about 1.6 cents per year and has a payback of about 93 years!