Compact fluorescent light bulbs (CFLs) have the following advantages over incandescent light bulbs when used properly: they last up to ten times longer, use about a quarter of the energy, and produce 90 percent less heat, while producing more light per watt. For example, a 27-watt compact fluorescent lamp provides about 1,800 lumens, compared to 1,750 lumens from a 100-watt incandescent lamp. CFLs are most efficient in areas where lights are on for long periods of time.