Dozens of Canadian cities, towns and communities will fade to black Saturday night, switching off their lights to mark a global effort dubbed Earth Hour.

Aimed at promoting electricity conservation and lowering carbon emissions, Earth Hour will take place between 8 p.m. and 9 p.m. local time around the world.

More than 240,000 people and almost 18,000 businesses in countries as far-flung as Botswana, Vietnam and Denmark have signed up as participants this year via a website groaning under the strain. The number of people marking the event is expected to be far higher, however.

About 55,000 Canadians have registered, just behind the United States and ahead of Australia. But 70 per cent of Canadians polled recently said they planned to mark the hour, organized by the World Wildlife Fund.

Businesses and government offices across the country plan to flick off their lights for the hour. National sites will also go dark, including Toronto's CN Tower and Eaton Centre, and Niagara Falls; Vancouver city hall and its Olympic flag; as well as Halifax's MacDonald Bridge and Parade Square.

Global landmarks such as Sydney's Opera House, San Francisco's Golden Gate Bridge, San Francisco's Alcatraz prison and Chicago's Sears Tower also planned to shut off their lights.

Grammy-winning singer Nelly Furtado will play a free concert at Toronto's Nathan Phillips Square, starting at 6:45 p.m. local time until 9 p.m. Power for the event will be supplied by Bullfrog Power, a company that uses emission-free sources like wind and water.

"This has really just blown up across Canada," said Tara Wood, spokeswoman for the World Wildlife Fund in Canada. "Canada is really going to be the shining star in this global effort."

To mark the event, the home page for Google, the world's most popular internet search engine, has changed its white background to black and includes the message, "We've turned the lights out. Now it's your turn."

Canadians weigh in on Earth Hour

Most people who posted comments to CBCNews.ca said they planned to participate.

Kristy Leger, of Allison, N.B., said she will take part "with friends and candlelight (pure beeswax) probably discussing the issue and enjoying a glass of wine."

Students in the Grade 3/4 class of the South Shore Education Centre in Nipissing, Ont., called it a "great event."

"Our teacher told us that when we grow up we get to run the world and we think you grown ups should help us; give us this headstart, so that when we grow up we don't have to live in a toxic wasteland!" the class wrote in a posting.

"Our class will mark this hour by creating crafts to show what the world may look like if nobody did anything to help save the planet."

Others were less impressed by the movement.

Eric Kasap, from Ottawa, calls it "a meaningless exercise that will do nothing other than to briefly assuage the guilty consciences of hypocrite liberal urban/surburban dwellers. They talk the talk, but in the next breath, leave their 3000 sq. ft. homes to jump into their 5000 lb. SUVs to drive 100 miles to their 2000 sq. ft. cottages to jump into their 200 hp motor boats, and so on."

Another Ontario poster who called himself Jonny Venom said he "will not participate in this fraud" and noted that he turns off his lights each night between 11 p.m. and 6 a.m.

The event, spearheaded by the World Wildlife Fund, started in Sydney, Australia, in 2007. More than two million people and businesses shut off their lights for an hour, resulting in a 10 per cent reduction on the country's electrical grid.

With files from the Canadian Press