While compact fluorescent lights have been larger than their incandescent equivalent bulbs, the newest lights are less than one half inch larger than the equivalent 60 watt incandescent bulb. In the future manufacturers promise even smaller lights. For now it is wise to measure your fixture before you shop for a compact fluorescent light. The best places for compact fluorescent lights are in frequently used fixtures that are on for at least three hours at a time. Difficult to reach fixtures are also good places to put compact fluorescent lights.
Fluorescent light is from a linear source which means it is spread out.
That is good because there is less glare even though the light can not be directed as well as an incandescent light. This means that compact fluorescent lights are good for area fixtures, but not so good for spot lights. At startup they take about 1.5 minutes to reach full brightness. For most uses this is a minor inconvenience. Three-way compact fluorescent lights are now being designed.