Research Project-Lighting Pros of CFL lamps are up to four times more efficient than incandescent bulbs you can replace a 100-watt incandescent bulb with a 22-watt CFL and get the same amount of light. CFLs use 50-80 percent less energy than incandescent lights. CFLs initially cost more but are less expensive in the long run because they last much longer. Disadvantages of CFLs, not every bulb is suitable for every job, so you must find the right match and the mercury content in CFL.