Events held in the city, as well as power-saving efforts by businesses and individuals, meant electricity consumption was down 5% during the hour from 8.30pm to 9.30pm compared to the previous Saturday.
In Cromwell and Wanaka there were even bigger savings, residents turning off lights to amount to a 10% saving, Delta network services manager Lindsay McLennan, of Dunedin, said.
In the Wakatipu basin, power consumption was down 5% and in Alexandra, Roxburgh and Omakau 4%.
The savings in Otago were greater than the national average of 3.5%.
New Zealand was the first country to "power down" for an hour as part of a global initiative, started in Sydney in 2007, to highlight the threat of climate change.
The Chatham Islands made the first move, by switching off its diesel generators.
Soon after, the exterior lights of Auckland's Sky Tower, were turned off.
Dunedin Earth Hour committee member Charlotte Flaherty said about 1000 people gathered in the Octagon where lanterns were hung from trees and paper boats holding candles were placed in the water fountain.
Street lights, as well as lights from businesses and restaurants, were turned off meaning the only thing electric in the Octagon was the atmosphere, Mrs Flaherty said.
The bells at St Paul's Cathedral and First Church were rung throughout the hour as many people enjoyed dinner and drinks by candlelight at the bars around the Octagon.
Otago District Health Board group manager diagnostic and support services Sonja Dillon said emergency battery operated ceiling lighting was turned on at Dunedin Hospital so other lights could be safely turned off.
Women dressed as Florence Nightingale went through the wards with lamps to see which ward had made the best power saving effort.
At Wakari Hospital wards also turned off their lights, with one ward having a special supper in the darkness.
Central Otago's main Earth Hour event took place in Pioneer Park at Alexandra, where hundreds of people gathered with torches and candles from 8.30pm.
Shapes made by people carrying lights were filmed and streamed live on to the internet from a webcam situated on Alexandra's clock on the hill.
Energy-efficient light bulbs were also given away by the Central Otago District Council.
Following New Zealand's lead, time zone by time zone, nearly 4000 cities and towns in 88 countries joined the event, sponsored by the World Wildlife Fund.
United Nations Secretary-general Ban Ki-moon called Earth Hour "a way for the citizens of the world to send a clear message: They want action on climate change".
Earth Hour organisers say there is no uniform way to measure how much energy is saved worldwide.
