Lumens: Lumens tell you how much light the bulb produces. When replacing incandescent bulbs, match the lumens you want rather than the watts you may not need.
Base-up / Base-down: Not all CFLs are the same. Some manufacturers caution against installing their CFL base-up. Read the label to see if base-up installation may shorten the life of the bulb.
Enclosed fixtures: Indoors, some CFLs should be installed only in open fixtures. Outdoors, in cold climates, enclosed fixtures are best.
Interference: CFLs may interfere with other electronic devices in the home like radios, TVs, or portable phones. Consider that when locating lamps.
Electronic timer and photocells: Most CFLs are not designed for use on circuits controlled by electronic timers or photocells. When replacing outdoor lighting, and for all your lighting needs, read the package label to find CFLs that will work best for you.
Remember: No "one-size fits all". Read the package labels and look for Energy Star® to be sure of efficiency.