Millions of Canadians are expected to turn off the lights Saturday during the third annual Earth Hour, an event that plunges cities around the world into darkness to heighten awareness about climate change.

They will be part of an estimated one billion people worldwide who are expected to turn the lights off at 8:30 p.m. local time.

Earth Hour was first started by the WWF in Sydney, Australia in 2007 as a way to reduce power use and send a message about the dangers of climate change.

Since that first year, the one-hour, voluntary blackout has spread like wildfire. Organizers expect more than one billion people in 126 countries to participate in this year's event, which has already begun in Australia and New Zealand, and across Asia.

In Canada, the event attracts a number of participants that is unmatched by nearly any other occasion, according to Keith Stewart, WWF Canada's climate change director.

"In terms of participation, the only time you get more Canadians doing the same thing at the same time is watching the gold medal hockey game," Stewart told CTV News Channel Saturday. "We had over 10 million Canadians participate last year. The skylines do go significantly darker."

Traffic lights and safety measures are not affected by Earth Hour.

In Edmonton

There will be a number of activities held in Churchill Square to mark this year's Earth Hour, including performances by fire dancers and singers, bannock making and a craft section for kids.  

While many are planning to take part, The Canadian Brewhouse says it cannot shut off its power because the pub is expecting 500 Ultimate Fighting Championship fans who are coming their to watch a broadcast of a George St. Pierre fight Saturday evening. 

"There would be a riot for sure," said pub co-owner Matt Woods.  "I would not want to be in here if I did turn it off."

Epcor will be logging power usage in Edmonton during Earth Hour and officials should be releasing the results Sunday morning. 

Last year Edmonton reduced its power consumption by 5 per cent.  Some Calgarians are challenging the City of Champions this year to see which city can reduce their power consumption the most. 

For information about Edmonton Earth Hour events click here.

Across Canada

Canadians may choose to spend a quiet evening at home, reading or socializing by candlelight, or they may opt to join an Earth Hour event.

Free concerts in Halifax and Toronto are some of the marquee events Canadians can attend. Many communities across the country are hosting smaller-scale affairs, such as live acoustic music by candlelight at churches and coffee shops, and yoga by candlelight.

A more complete list of Earth Hour events can be found at WWF Canada's Earth Hour website.

No matter what a person chooses to do to mark Earth Hour, the end goal of the symbolic hour of darkness remains the same.

"It's about giving people a chance to make visible what's usually invisible," Stewart said. "And that's the desire for action on climate change and a willingness to be part of the solution."

Andy Riley, a WWF worker in Sydney who came up with the idea for Earth Hour, said he hoped this year's event would encourage world leaders to push for a stronger climate agreement than the one reached at the Copenhagen climate change summit last December. That agreement failed to include binding rules on reducing the pollution that is blamed for global warming.

"What we're still looking for in this coming year is a global deal that encourages all countries to lower their emissions," Ridley told The Associated Press on Saturday. "China is going to have to be a big part of that, but so is every other major economy."