'Everlasting' light bulb on the way

Colin Humphreys and his gallium nitride bulbs

By BBC News Online's Damian Carrington

Changing light bulbs could become a thing of the past as future homes will be lit by everlasting bulbs wired directly into the walls.

Professor Colin Humphreys, a material scientist at Cambridge University claims that it is the biggest step forward in lighting technology since Edison invented the tungsten bulb.

The semiconductor making this possible is called gallium nitride. "I think that gallium nitride is the most important new material since silicon," said Professor Humphreys, speaking at the British Association's Festival of Science in Sheffield, UK.

Within five years, it is also expected to lead to new, "sharper" lasers which will allow an entire music collection to be stored on a single disc and more accurate surgery and dentistry.

Gallium nitride emits an intense blue light when an electric current is passed through it, making it the first bright blue, light-emitting diode. But it uses just 20% of the power consumed by an equally bright conventional bulb.

Brightest and best

Adding the element indium, creates an increasingly rosy tone, through to red. And for white light, a phosphor coating can be added to the outside, just like fluorescent tubes today.

"With normal intermittent use, they would last a lifetime," said Professor Humphreys. "So once fitted, you may never have to change another lightbulb. The potential market is huge."

Bulbs are being tested at the moment in traffic lights in London and Bristol where they are expected to last 10 years. Conventional bulbs last just six months.

The power savings would be huge too - keeping the UK's traffic lights running requires the equivalent of two medium-sized power stations.

Blue lasers using gallium nitride would allow compact discs to be produced with enormous recording capacity. This is because the shorter wavelength of blue light makes it possible to store information more densely than with the red lasers now used.

"It should prove possible to have all of Beethoven's symphonies or all of Madonna's songs on a single CD," said Professor Humphreys.

In addition, blue lasers could improve laser surgery and dentistry, because they can be focused more finely than red lasers. Gallium nitride would also be useful for making high-power transistors which could give mobile phones a much greater range than they have at present.

The gallium nitride blue LED was invented in 1994 by Shuji Nakamura of Nichia Chemical Industries in Japan.