The Cambridge University scientist is making a material that he and others believe could help to cut emissions of carbon dioxide and other greenhouse gases by 15 percent -- by making low-voltage, longer-lasting and more efficient light bulbs.

"We can save about 15 percent on CO2 emissions, not by installing wind power which a lot of people don't like, nor by using our cars less, but simply by developing gallium nitride-based lighting," said Humphreys, the Goldsmiths' Professor of Materials Science at the university's Department of Materials Science and Metallurgy .

Gallium nitride is a compound that emits intense light. Humphreys believes the material that scientists are creating in the laboratory atom by atom could be the most important new electronic material since silicon.

He is convinced that using it in a light-emitting diode (LED), a device that emits visible light when an electric current passes through it, could help to curb global warming.

LEDs are already used in digital clocks, bicycle lights, mobile phones and traffic lights. Unlike normal light bulbs, which burn out quickly after about 1,000 hours, an LED lasts 100 times longer and fails gradually.

DENVER GIVES THE GREEN LIGHT

Under the 1997 Kyoto Protocol, developed nations will have to cut emissions of greenhouse gases to 5.2 percent below 1990 levels by 2008-12. Humphreys said that by 1997 most nations were already 5 percent above 1990 levels.

"So effectively this is saying that nations commit to reduce their CO2 levels by about 10 percent."

Lighting in Britain and other developed nations accounts for about 20 percent of all the electricity used. In poorer countries the figure rises to 40 percent, according to Humphreys.

The Japanese firm Nichia used gallium nitride to make the first LED to emit blue light in the early 1990s.

Humphreys and other scientists around the globe are using the material to develop tiny LEDs that emit a soft white light, instead of the current harsh one, which could eventually be five times more efficient than normal light bulbs.

"At the moment in the laboratory, gallium nitride is three times as efficient as light bulbs but in the next few years it will be five times as efficient, I'm sure," he said.

Singapore, Denver, Colorado and other cities have replaced old traffic lights with LEDs and have seen considerable financial and energy saving, according to Humphreys.

"Although the capital cost of LEDs is greater than conventional light bulbs, over 10 years which is the lifetime of these LED traffic lights, Denver calculates it will save $5 million," said Humphreys.

But the real savings could come when homes and offices can be converted to LEDs.

BRIGHT FUTURE

"At the moment the white LED is a harsh white. Coaches and cars will soon have white LEDs inside but for homes it will not be very acceptable," said Humphreys.

He estimates it could take about 5-10 years before the technology to produce gallium nitride LEDs with a more subtle white will be available.

But when this happens it could lead to real savings.

In addition to being more economic and efficient, LEDs in the home are also very safe because of their low voltage and they never become hot like other light bulbs.

"It's 4 volts but it gives off a brilliant light. One reason they are so efficient is that they stay cold. Light bulbs waste a lot of energy because they get incredibly hot," said Humphreys.

White LEDs won't solve global warming but they could be part of an overall plan to lower emissions of greenhouse gases.

Instead of lighting taking up 20 percent of the electricity LEDs could cut it to five percent which translates to a 15 percent saving on overall electricity use.

"You need a number of power station to provide electricity. If you reduce the electricity demand by 15 percent, you can close 15 percent of power stations and then you save 15 percent of the CO2 they emit," said Humphreys.