A compact fluorescent lamp (CFL), also known as a compact fluorescent light or energy saving light (or less commonly as a compact fluorescent tube [CFT]), is a type of fluorescent lamp. Many CFLs are designed to replace an incandescent lamp and can fit into most existing light fixtures formerly used for incandescents.

Compared to general service incandescent lamps giving the same amount of visible light, CFLs use less power, have a longer rated life, but have a higher purchase price. In the United States, a CFL can save over 30 US$ in electricity costs over the lamp’s life time compared to an incandescent lamp, and save 2,000 times its own weight in greenhouse gases.[2] Like all fluorescent lamps, CFLs contain mercury, which complicates their disposal.

CFLs radiate a different light spectrum from that of incandescent lamps. Improved phosphor formulations have improved the subjective color of the light emitted by CFLs such that some sources rate the best ‘soft white’ CFLs as subjectively similar in color to standard incandescent lamps. (see Energy Efficiency Chart at bottom of page)

Energy efficiency (source: Wikipedia)

The chart shows the energy usage for different types of light bulbs operating at different light outputs. Points lower on the graph correspond to lower energy use. For a given light output, CFLs use 20 to 33 percent of the power of equivalent incandescent lamps.

Since lighting accounted for approximately 9% of household electricity usage in the United States in 2001, widespread use of CFLs could save as much as 7% of total US household usage.

Electrical power of lights with approximate equivalent luminous power

Characteristic luminous power (lumens) CFL power (W) Incandescent power (W)
450 9–13 40
800 13–15 60
1,100 18–25 75
1,600 23–30 100
2,600 30–52 150