Buildings and homes across the country went dark Saturday night as Canadians took part in the fifth annual Earth Hour.
But early results suggested fewer people turned off the lights this year.
In Toronto, energy use fell by 115 megawatts between 8:30 p.m. and 9:30 p.m., a drop of about 5 per cent, said Jennifer Link, a spokeswoman for Toronto Hydro.
Last year, the city's Earth Hour efforts saved 296 megawatts; in 2009, it was 454 megawatts.
Meanwhile, Nova Scotia Power reported saving 10 megawatts of power, a significant drop from last year's 18 megawatts.
Utilities in other provinces said it could take them until Monday to calculate the results.
Some experts say Earth Hour is losing steam now that the novelty has worn off.
But Steven Price of the World Wildlife Fund, which runs Earth Hour, said the goal isn't to boost energy savings during the event.
"What we want is the participation, because it's an awareness campaign that allows people to take some action" to fight climate change, he said after Saturday's Earth Hour.
A record number of countries and municipalities signed up for this year's event, he said.
Over the next few days, the organization will conduct surveys to determine how many people participated, Price said. He expects there to be about one-billion people worldwide.
In Toronto, hundreds watched as the billboards in Dundas Square suddenly shut down.
Still, some in the crowd said they were disappointed to see so many stores stay brightly lit.
"There's still too many lights on," said Brandon Marton, pointing to the store signs and street lights illuminating the area. "You really don't get the full effect."
Others were dismayed to find no public celebrations, like there had been in previous years.
"It's unfortunate, because it seems to draw people," said Dave Makarchuk of Guelph, Ont., who expected some kind of outdoor show to mark the occasion.
"I know it drew us here," he added.
Earth Hour began in Australia in 2007 and has since spread to more than 130 countries.