Homes and businesses across Northern Ireland are being urged to switch off lights and lamps for one hour tonight to commemorate the 100th anniversary of the outbreak of the First World War.
In a symbolic, nationwide gesture, houses and buildings throughout the UK will be plunged into darkness at 10pm, with just a single light or candle burning for an hour.
The dimming of the lights is just one of a number of events taking place to mark 100 years since Prime Minister Herbert Asquith declared that Britain was at war with Germany on August 4, 1914.
Tens of thousands of house-holders and hundreds of buildings, including the Houses of Parliament and St Paul's Cathedral in London, are expected to join in the Lights Out plan.
Closer to home, special events are being held in Northern Ireland to mark the start of the conflict, which claimed the lives of millions of soldiers from around the world.
In Belfast, the outbreak of the First World War will be remembered at a centenary commemoration service to be held in St Anne's Cathedral, tonight at 7pm.
The service is expected to be attended by Secretary of State Theresa Villiers, Heather Humphreys TD, Minister for Arts, Heritage and the Gaeltacht for the Republic, and senior figures from the main churches in Northern Ireland.
The Queen will be represented in Belfast by the Duke of York, who will read a lesson and will light a candle to mark the occasion.
The service will be conducted by the Dean of Belfast, the Very Rev John Mann. Young people will light five candles during the service, each representing a year of the war.
Admission to the event is by invitation only.
Elsewhere in Northern Ireland, a number of candlelit vigils are being held to mark the occasion.
In Belfast, a wreath laying ceremony will take place at 10pm, as City Hall is plunged into darkness.
In Coleraine, a vigil will be held in the town centre at 10.30pm, followed by a tolling of church bells at 11pm, while in Carrickfergus, the Knockagh Monument will be lit up for an hour at 10pm.
In Antrim, a candlelit vigil will be held followed by the release of lanterns into the sky.
Meanwhile, the great-niece of a First World War soldier will join dignitaries, including the Duke and Duchess of Cambridge, at a special ceremony this evening.
Helen Jones will be the first member of her family to visit the grave of her great-uncle Private George Bellamy at St Symphorien military cemetery near Mons in Belgium.
Mrs Jones and her husband will be among a guest list which includes the Duke and Duchess of Cambridge and Prince Harry.
The 57-year-old plans to lay some flowers on the grave of Private Bellamy, of 2nd Battalion the Royal Irish Regiment, to say thank you for the sacrifice made by him and millions of other soldiers.
The mother-of-three, who will be joined on the trip by her husband, said she expected it to be an emotional occasion.
"I really want to lay some flowers on George's grave and just say 'you know what, thanks, because you changed the world for us'. Without it, it wouldn't be the same," she said.
"They just gave everything, a whole generation almost of young men just disappeared. We just can't credit it."
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