Compact fluorescent lamps are designed to replace incandescent lamps, because the former use less power and have a longer rated life.
Since CFLs use less power to supply the same amount of light as an incandescent lamp, they can be used to decrease energy consumption at the location in which they are used. In countries where electricity is largely produced from burning fossil fuels, the savings reduces emissions of greenhouse gases and other pollutants; in other countries the reduction may help reduce negative impacts from radioactive waste, hydroelectric plants, or other sources; see environmental concerns with electricity generation for details.
But such bulbs are not so environment-friendly as it may seem. Broken CFLs are an immediate health hazard due to the evaporation of mercury into the atmosphere. The U.S. Environmental Protection Agency recommends that, in the absence of local guideline, fluorescent bulbs be double-bagged in plastic bags before disposal.
When such a bulb is broken it’s better to vacate the room and open windows for fifteen minutes to allow any mercury vapor to air out, then clean up the breakage while wearing protective gloves, and use double plastic bags for all broken pieces.