A type of fluorescent light bulb that will fit in a socket designed for a traditional incandescent light bulb. Not only do the use less electricity to produce similar amounts of light (money you save), they also produce less heat (lower cooling bills). This is because only 10 percent of the energy consumed by an incandescent bulb actually produces light. The remaining 90 percent generates heat, that is wasted...or heats up your house in the summer. They cost more than regular light bulbs (~$15 US), but they last longer than incandescents and use less energy, theoretically paying for themselves in time. Just don't put them in a lamp you may knock over....