CFL refers to compact fluorescent lamps. They contain argon and mercury vapor within a spiral shaped lamp. When the gas gets excited, they produce ultra violet light. This light in turn stimulates a fluorescent coating painted on the inside of the tube. Visible light gets emitted when the inside coating absorbs energy. The inside coating is made of phosphor which is painted on the inside of the bulb. The phosphor is very efficient in this process of converting electrical energy into visible light.
These lamps have become popular alternatives to the conventional incandescent lamps due to their low power consumption. CFLs last more than incandescent lamps, even 8 times more hours. They also require less electrical power to produce an equivalent amount of light.
Unfortunately, compared to the incandescent bulbs, handling and disposal of CFLs are more complex. This is because they contain mercury that makes the usage risky. Mercury is highly toxic. In case the bulb breaks, the toxic mercury vapor escapes. A small amount of mercury powder can also be released. This powder is dangerous for human health. And so their disposal too becomes a problem. There is a necessity for a very safe clean up. Why shape of CFL lamp differs from incandescent lamp? Why does a tube light have a glow delay compared to CFL?