The German consumer organisation Warentest tested 18 energy-saving bulbs in 2008, and after 10,000 hours, three of the 18 bulbs had stopped working completely with an average reduction in brightness of 22% for the remaining 15 bulbs.
The US Department of Energy tested 124 bulbs for 2,400 hours (which it should be stressed is much less than the intended working lifetime of 10,000 hours), of which found that 28% no longer gave a decent light output. In contrast, normal filament light bulbs lose perhaps 7% of their brightness when the filament "goes", which is after about 2,000 hours.
The Energy Savings Trust purports that a 11-14W energy efficient bulb is equivalent to a 60W traditional bulb, which is put on the packet by most British lighting manufacturers. However, the European Commission has issued a warning that these claims are "not true". On a consumer website it claims that: "The light output of 15W compact fluorescent lamp is slightly more than the light output from a 60W incandescent."
As from September 2011, 60W clear incandescent bulbs will be banned and from last August it became illegal for retailers to import 100W, frosted or pearled incandescent light bulbs, or to sell them once their current stocks have run out, leaving low energy bulbs (low energy halogen or compact fluorescent lights CFLs) as the only option.
There are certainly saving in the amount of electricity required to run the different kinds of bulb, however. Dr Paula Owen at the government-backed Energy Saving Trust, is quoted as saying that good energy saving light bulbs would only be noticeably dimmer after six to ten years. She noted: "Typically, a low energy light bulb used in a living room, for example, will last 10 times longer than a traditional one. In this time, the householder will have saved about £65 on their energy bill.