Compact Fluorescent Lamps, usually billed as energy-saving - or long-life - bulbs, are certainly worth having. However, as BBC Radio 4's "More or Less" pointed out this week, manufacturer's claims do exaggerate. The rule of thumb adopted by their association is that an incandescent light-bulb's wattage should be divided by 5 to give the equivalent CFL. Thus 12-watt CFLs are marketed as the equivalent of a traditional 60-watt bulb. In fact, for various reasons the conversion factor is nearer 4. A US technical body believes that 3 is more realistic.
One should also remember that bulbs should be disposed of safely.