For the fifth year in a row, Hong Kong's famous skyline dimmed last night as residents embraced the green mantra of Earth Hour.
But for one university professor who specialises in sustainable development, it was a chance to protest against what he called a gimmick that did more harm than good.
"There are more than 8,700 hours in a year. What can one hour contribute?" said Professor Edward Ng Yan-yung from Chinese University's school of architecture. "Some say the event raises awareness, but my take is: what awareness will it bring? The dilemma is that one goes away thinking that one has already saved the earth."
For one hour from 8.30pm, thousands of buildings switched off their lights to mark the initiative, which Hong Kong first adopted in 2009. Organised by the conservation body WWF, Earth Hour debuted in Sydney in 2007 and has since spread to 152 countries.
Ng says he never turns on his office light at night because he works mainly on his computer and has a desk lamp that he uses sparingly.
"But I will turn on my office light during Earth Hour, just to remind myself what I have been doing for the rest of the year."
A WWF-Hong Kong spokeswoman says it was a symbolic event aimed at getting people to think about the ecological impact they make on the world.
"Participation in Earth Hour symbolises a commitment to change beyond the hour," she says.
Findings from a light pollution study released last week showed Hong Kong could be the world's worst city for light pollution, with Tsim Sha Tsui recording 1,200 times the brightness of a natural dark sky.
Last night, more than 3,800 companies and buildings joined the event, up from 3,300 last year. All the universities, and about 370 primary and secondary schools also took part.
Landmark buildings on Hong Kong Island that plunged into darkness included the International Finance Centre, Legislative Council complex, Hopewell Centre, Cheung Kong Centre, HSBC building and Convention Centre, while in Kowloon, the International Commerce Centre and 1881 Heritage switched off their lights. The Tsing Ma bridge, which connects Tsing Yi and Ma Wan, also went dim.
Last year, electricity usage dropped 4.27 per cent during Earth Hour, equal to saving 146 tonnes of carbon dioxide, which would take more than 6,300 trees to absorb in a year.
In Macau, major buildings are also doing their part. A new initiative will see 13 hotels including the Venetian Macau and Grand Hyatt Macau switch their lights off on the first Tuesday of every month.
But Ng called on WWF to let people know Earth Hour was just a gimmick so it could spur them to do more. "It's not just about switching off, it's about using light better," he said.