Electricity to illuminate advertising signs and buildings is costing Australians more than $100 million each year. And much of the light generated is lost to the night sky, creating a generation of children who only see constellations in planetariums or on television, astronomers have warned.

The glare from outdoor night lighting is so invasive that in some parts of Melbourne's west it has wiped out backyard access to even such familiar beacons as the Southern Cross.

Night lighting was not only ruining the night sky for astronomers but was causing unnecessary economic and environmental damage to Australia, said Mr Geoff Dudley, director of the light pollution action section at the Astronomical Society of Victoria, where $23million is spent each year fighting the forces of darkness.

Dr David Crawford, the executive director of the International Dark Sky Association, said light pollution also adds to environmental degradation through the mining and burning of fossil fuels to generate this electricity.

The main causes of light pollution in Australia are illuminated advertising signs and decorative lighting on bridges and buildings, Dr Crawford said.

He estimated that 2.5 per cent of Australia's total electricity production is used for night-time outdoor lighting. About 30 per cent of this lighting ends up in the night sky, he said.

In Australia, this is equivalent to 1119 million kilowatt-hours of electricity, more than the electrical production of Ethiopia, Mr Dudley said.

"Australia-wide, this costs about $100 million a year and results in the production of over one million volumetric tonnes of the greenhouse gas carbon dioxide. The problem is not trivial," he said. "Light pollution is costing the country a lot of money and is wasting a lot of natural resources."

In Victoria, 280,000 tonnes of coal are burnt annually to light up the night sky, Mr Dudley said. One of the state's worst offenders for projecting light into the sky was City Link's Bolte Bridge, he said. But urban skies also glow from the light reflecting off the ground and buildings.

Dr Crawford said although lighting was necessary for night-time recreation, security and safety, there were many instances where it was superfluous.

To reduce the amount of light reflected into the sky, billboard lighting and business signs should be turned off at night, he said. Unnecessary lights should also be turned off and security lighting kept to the level needed for the job.

Mr Dudley said some councils were introducing night-time lighting to buildings as decoration and further degrading the night sky.

"It really is crazy that some councils are not coming up with outdoor night-lighting codes to reduce the waste and bring down costs."

Although there are Australian standards on lighting, Mr Dudley said the existing obtrusive lighting standard was inadequate because it did not apply to advertising signs.

"What state governments ought to do is introduce their own outdoor night-lighting codes and, where standards are deficient, make up for that in the code."