The Four Courts and the Custom House were among public buildings in Dublin where lights were switched off for the past hour.
They are just two of the buildings around the world involved in the campaign to put towns and cities in semi-darkness between 8pm and 9pm.
The gesture is part of efforts to raise awareness about climate change.
The move is part of the global initiative 'Earth Hour' which has already taken place in Australia this morning which will see millions of people switch off their lights.
Astronomy Ireland held a special astronomy event in Phoenix Park, Dublin with a hope to seeing some objects usually not seen due to light pollution.
'Earth Hour is a wonderful opportunity for people and businesses to switch off and switch on to a new way of thinking,' Mr Gormley said.
'We can demonstrate through Earth Hour that individual action can make a difference on climate change,' he said.
Sydney was the first major metropolis to mark 'Earth Hour', a self-imposed 60-minute black-out, with the lights on landmark buildings, corporate skyscrapers, businesses and homes switched off from 9am Irish time.
From there the initiative, which aims to engage the community in combatting global warming, will see lights dimmed or turned off at 8pm local time in Asian cities such as Bangkok and Manila, before spreading further to Europe and the Americas.
'Earth Hour' founder Andy Ridley, who has said up to 30 million people could participate this year, said he was amazed at how far the initiative had spread since it was launched by environmental group WWF in Sydney a year ago.
‘When we first talked about it, right at the beginning, our dream was to come up with something that made sense to a lot of people to do,’ he said,
‘And what seems to have happened is that it does seem to make sense to a lot of people to do it.’
'Earth Hour' encourages governments, companies and homeowners to voluntarily switch off power to non-essential appliances for one hour to illustrate how, by working together, people can make a difference by using less energy, thereby producing fewer greenhouse gas emissions.
