'It just seems ridiculous to have a huge sign flashing gaudy messages hundreds of yards across,' says Stephen Brown, indicating a dazzling LED billboard on the roof of a Tsim Sha Tsui mall that dominates the view from his Wan Chai office.

'It is tasteless, offensive and also breaks the ridge line of one of the most famous harbour views in the world. Maybe every other building will now follow suit.'

He may be right; at least one advertising executive predicts that within a decade, all the illuminated signs in the city will be LED displays.

'Though the initial investment is larger, they are colourful and can project graphics [and are] less vulnerable than neon lights and more effective,' said Mak Siu-tong, chairman of Convey Advertising which is one of four agencies in the city providing LED displays.

He said only 1 per cent of the rooftop signs in Hong Kong were LEDs last year, but now they accounted for 3 to 4 per cent.

Friends of the Earth environmental affairs manager Hahn Chu Hon-keung said he had received several complaints from mainland tourists about the light from the LED signs of a cosmetics shop in Nathan Road.

LED signs that have attracted the most complaints to the Friends of the Earth include one for a Bonjour cosmetics shop in Nathan Road, a rooftop sign for Prudential Insurance on Star House, the Samsung sign near Revenue Tower and the rooftop sign of iSquare.

Ron Hui Shu-yuen, a professor in the department of electrical engineering at City University, said LEDs, or light-emitting diodes, were an energy-saving light source.

The government is switching all its traffic lights to LEDs and estimates it can save 70 per cent of its power bill for the lights, but advertisers have also discovered they can get more bang for their buck.

Hui said: 'It is a good technology - environmentally friendly and energy saving - but some uses have been abusive.'

LED beams were directional and concentrated, so the glare could easily affect residents, especially those living on the same level, he said.

Former Wan Chai district councillor Ada Wong Ying-kay said she had received complaints about light pollution - including some from Mid-Levels residents who said their homes were lit up like a disco by signs across the harbour.

'Many people are resentful about light pollution and I am also strongly dissatisfied about it,' she said. 'The earth's resources are scarce and these kinds of signs are just wastage. They are not environmentally friendly.'

Mak, a veteran advertising agent, said the set-up cost of LED billboards was still high and limited the technology to those who could afford it.

The cost could be as high as HK$20,000 a square metre and rooftop signs are commonly around 1,000 square metres.

Some high-end buildings or malls, like The One, set up their own billboards and rented them to advertisers for as much as HK$1 million a month. All they needed to do to change an advertisement was make an adjustment in a computer system.

'So there is a huge potential market,' said Mak, but adding that one of the drawbacks on the environmental side was that the signs had to be kept on in the daytime to be visible.

A spokeswoman from iSquare said it turned off its LED signs and decorations every day after 11pm. The One had no comment.

Complaints to the government about light pollution are rising. There were 87 complaints in 2007, 159 in 2008 and 377 last year. In the first eight months of this year, the Environmental Protection Department alone received 152 complaints.

Chu of Friends of the Earth - whose group has long been campaigning for lights to be dimmed - said that although the brightness of LED displays could be adjusted, shops were unlikely to turn them down. 'It seems that billboards from different shops are just competing for customers by their brightness.'

He was happy to see an increasing market share for LED lights, which were an energy-saving tool that could help deal with global warming. 'But I hope advertisers have a mindset of sustainable development in designing signboards,' he said. 'If not, it could create severe light pollution problems, especially in a city with such poor urban planning.'

Chu said the government finished a consultation on light pollution last year but had never initiated legislation. He suggested dividing the city into different zones and imposing different light curfew hours.

The Environment Bureau said it had commissioned a consultancy study on external lighting, but was still consolidating the findings.

A spokeswoman said the bureau would 'gauge views from relevant stakeholders and advisory bodies' and make recommendations on how to address issues arising from external lighting.