Ottawa residents who shut off the lights during an international climate-change awareness event Saturday evening reduced the city's power consumption by four per cent compared to the same time at the previous Saturday, Hydro Ottawa reported.

"If you consider that lighting is only about 14 per cent of the overall load for the whole city, that's a significant drop," said Bruce Bibby, who is responsible for energy conservation at the local utility.

Ottawa was one of 150 communities across Canada and others around the world that pledged to turn off their lights and non-essential electronics for one hour starting 8 p.m. local time Saturday night as part of an event organized by the World Wildlife Fund.

In Ottawa, participants turned off the lights at the Peace Tower and in many Ottawa homes and businesses.

Consequently, they used 892,467 kilowatt hours of power between 8 p.m. and 9 p.m., or 37,114 kilowatt hours less than they did during the same hour on March 24, Hydro Ottawa said in a news release. 

The average household in Ontario uses just under 1,000 kilowatt hours a month, or 33 kilowatt hours per day, so the energy saved in Ottawa during Earth Hour would have been enough to power around 1,125 extra homes for an entire day.

The impact in Ottawa was slightly below the overall decrease in power consumption in Ontario during Earth Hour, which was five per cent.

Bibby said he expects to see greater involvement if the event is held again next year.