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Last Updated: Monday, 23 October 2006, 14:40 GMT 15:40 UK
The cost of lighting the world
London seen from space
Light pollution means cities like London are visible from space
Electric light is one of the greatest advances of the modern world, but, with the rise of light pollution, it has proved to be something of a mixed blessing.

The twinkles of the stars are fewer these days - drowned in the glare of Earthly light sources. Light pollution has become a problem, and not just for astronomers - although they are among the most frustrated with it.

"I think it's terribly important to see the stars," space expert Heather Couper told BBC World Service's One Planet programme.

"You get the impression that what light pollution is doing is knocking out the landscape of what's above us.

"Imagine if you lived on Venus, which is continually veiled with clouds - you'd never see the stars, and you'd be 'landlocked'; you could only look at your own landscape."

Good news

Much of the light generated on Earth is wasted, spilling out into space.

In terms of energy consumption, this is not very efficient.

Incandescent lightbulbs, the type which have a filament inside, account for around half of the lightbulbs in homes around the world. But only about 5% of the energy they use is actually turned into light. The other 95% is wasted.

LEDs (EyeWire)
Because LEDs are so small, we're able to put them into very efficient optical systems - waste light is significantly reduced
Mike Simpson, Philips Lighting
Paul Wade of the International Energy Agency (IEA) says that this is a dismal state of affairs.

"We estimate that around 19% of all electricity is being used for lighting in one form or another," he said.

"To put that in context, that's equivalent to using all the power produced by nuclear or hydro power, plus another 15% on top of that, just for lighting applications."

The IEA projects that the energy need for lighting will grow by around 80% between now and 2030 unless efficiency efforts are made.

However, Mr Wade added that the "good news" is that there are enormous inefficiencies in normal lighting practices, "which means an awful lot more can be done to get the same service for much less energy".

Indeed, it is believed that a major advance in light technology is not far away.

The latest advances have been light-emitting diodes - LEDs - and are developing at a very fast rate.

Because the individual LEDs are so small, they can be put into efficient optical systems, directing the light.

"With the conventional lighting equipment, a lot of the light that you want to go onto a building actually shoots past it and goes off into the night sky," said Mike Simpson, the technical and design director of the lighting division of electronics giant Philips.

"Because the LEDs are so small, we're able to put them into very efficient optical systems - which means that the waste light that we have doesn't completely disappear, but is significantly reduced."

Mr Simpson said that in total, at least 50% of the light that is currently wasted can be captured.

Bigger savings

Over the past five years, Philips has invested around 400m euros in "green light technology".

It now estimates that replacing all the standard lightbulbs in Europe with new energy-efficient ones could cut carbon emissions by 28million tonnes a year - the equivalent of 50million barrels of oil.

LED scoreboard for the Philadelphia Fliers
LEDs are becoming ever more commonplace
But even bigger savings could also be made by using light in a more selective and controlled way.

According to Paul Wade, that includes learning to make better use of daylight, and learning when to switch the light off.

"There are many options to use daylight more efficiently - including technologies which would automatically dim artificial lighting systems in response to rising daylight levels," he said.

"There are also occupancy sensors, which can tell when people have left the space and turn off the light."

Meanwhile, Philips is promoting an automated lighting control system, which is on when people are present but turns itself off when they leave.

"We estimate that by using very basic lighting controls for an office environment, you could probably save 50% of the energy," said Mr Simpson.

"We've all been past large office blocks in the city and seen the lights burning all through the night. It's completely unnecessary."

100m city lights project begins
09 Oct 06 |  West Yorkshire
Lighting is still in the Dark Age
17 Aug 06 |  Science/Nature
Paintings reveal pollution clues
09 Aug 06 |  Science/Nature

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