Daily Mail | November 19, 2009
By David Derbyshire

Energy-saving lightbulbs being used in millions of homes could lose up to 40 per cent of their brightness over the next few years, engineers warned yesterday.

A design flaw in compact florescent bulbs mean they become dimmer as they age, a report by the Institution of Engineering and Technology said.

Millions could need replacing long before their advertised lifespan of five or six years is reached.

The Government is phasing out traditional bulbs in order to meet Europe's climate change targets.

Although other types of low energy bulb are available - including halogen and LED lights - most households are being encouraged to use compact fluorescent lamps.

The Department for Environment, Food and Rural Affairs says CFLs use a fifth of the energy of traditional bulbs, saving a typical home at least £37 a year and cutting the UK's carbon dioxide emissions by five million tons.

However, independent retailers and critics say many of the low-energy alternatives are ugly, expensive and produce poor quality light. Doctors have warned that CFLs may cause rashes in light-sensitive patients.

A report in Engineering and Technology Magazine now warns that CFLs lose 'a significant amount of brightness' over time.

Even a good quality bulb could lose 20 per cent of its light over its 8,000-hour lifespan - while cheaper bulbs could dim even more. The problem is made worse because some manufacturers exaggerate how much light comes from CLFs in the first place, the report says.

'Consumers could end up with a CFL nearing the end of its life that emits just 60 per cent as much light as a supposedly equivalent incandescent bulb,' the report says. That means a CFL that begins life as bright as a traditional 100watt bulb, could become as dim as a 60watt bulbs.

CFLs give off light when a current passes through a gas-filled tube. The gas glows with ultraviolet radiation which lights up a coating of white phosphor on the inside of the tube. Over time, this coating loses some of its ability to light up.

Other low-energy bulbs don't have the same problem. A halogen light - which uses 70 per cent of the energy of a conventional bulb - remains bright throughout its life.

LED bulbs - which are beginning to appear in conventional bulb shapes and brightness - are also more reliable.

Editor in chief of Engineering and Technology Dickon Ross said most people were unaware that CFLs eventually lost their brightness.

'Our article goes someway to explaining consumers' dissatisfaction with CFLs and it's interesting that the major manufacturers have switched their focus to the development of LED lighting,' he said.

The Energy Saving Trust, which is funded by the Government, confirmed CFLs did lose brightness but claimed most people would not notice the difference.

Trust-approved bulbs should never fall below 76 per cent of their initial brightness, it added.