Your choice will vary depending on the degree to which the motion sensor reduces the total amount of time the incandescent light is on.

The energy consumed by the 26-watt CFL in nine hours is actually less than the energy consumed by the 75-watt incandescent in four hours. Consider that 26 watts is roughly one-third of 75 watts. Therefore, if the 75-watt incandescent bulb on the motion sensor is on for more than one-third the amount of time the 26-watt CFL would be on, you should go with the CFL. If the incandescent on the motion sensor is on for less than one-third the time the CFL would be on, you should go with the incandescent.

Don’t worry if you haven’t been keeping track of your lamp usage. Just think about your activity spaces:

For areas that are seldom occupied (laundry rooms, dens, storage closets, garages, or workshops) you might consider using the motion sensor with the incandescent bulb – especially if lights tend to be left on for long periods of time when no one’s around.

For areas that are used regularly (offices, bedrooms, dining areas, or living rooms) installing a motion sensor might not significantly decrease the total amount of time the lights are on. For these spaces, CFLs are preferred.