They are small fluorescent lights which fit into standard light sockets. They have longer lives and use less energy than a standard (incandescent) light bulb.
Yes, they need mercury to generate light efficiently. The mercury is used to produce ultraviolet light, which is then changed into light we can see by a special coating in the lamp. The coating is inert and poses no health risk.
Nowadays, the typical amount is around 4 milligrams per lamp – just enough to cover the tip of a ball point pen and just enough to last the expected life-time of the lamp.
The mercury cannot escape from an intact lamp and, even if the lamp should be broken, the very small amount of mercury contained in a single, modern CFL is most unlikely to cause any harm.
But it makes sense to avoid unnecessary contact with mercury; and a broken light bulb will also produce sharp pieces of glass. So it's best to deal with breakages sensibly, as described below.
Of course, we should avoid putting mercury into the environment where we can, so dispose of unwanted CFLs correctly, as advised below.
In the event of an accidental breakage of a CFL, normal good housekeeping is required.
As mentioned earlier, the amount of mercury contained in a typical CFL is very small, up to 5 mg and is unlikely to cause any harm to human health. The level of risks involved in the case of a broken CFL on carpet is no greater than that on hard surfaces, although it may take a longer while to clean up the affected area due to the nature of the carpet surface.
The above clean up procedure should apply, but minus wiping up with a damp cloth and more attention should be paid to residual CFL pieces or powder removal using sticky tapes.
The bags can then be discarded through your local council. All local councils have to make arrangements for disposing of hazardous household waste. Many local authorities have a special place for hazardous household waste at a civic amenity site or household waste recycling centre. The National Household Hazardous Waste Forum runs a website with details of these centres for chemicals, but which also applies to other hazardous wastes (http://www.chem-away.org.uk/). Alternatively contact your local council direct.
Further information on the environment and compact fluorescent lamps is available from the Defra website
Background information on mercury spills in residential settings is also available.
Last reviewed: 15 June 2010