Incandescent to CFL
This is probably the simplest of all retrofits, replacing a power-hungry incandescent light bulb with an energy thrifty Compact Fluorescent Lamp (CFL), also known as a compact fluorescent light. In comparison to incandescent bulbs CFL’s use only one-fourth the energy and last up to 10 times longer.
The most popular variety of CFL in the U.S. The tubular CFL, shown below, is more popular
is the spiral type shown below: in Europe and slightly more energy efficient: