The lights will go out at a historic Lincoln landmark next month to commemorate the 100th anniversary of the First World War.
On Monday 4 August Lincoln Castle will take part in Lights Out, a UK-wide event to mark the centenary of the conflict.
Council headquarters County Offices will also be taking part, as will landmarks around the country, including Blackpool Illuminations, the Houses of Parliament and Tower Bridge.
Councillor Nick Worth, Executive Member for Culture and Heritage, said: “A hundred years ago, the British Foreign Secretary Sir Edward Grey famously remarked that the lamps were going out all over Europe, as Britain declared war on Germany.
“What followed was one of the darkest periods of our history, and this event is a way to remember the sacrifices of all those involved.
“People around the county can also take part by turning off their lights from 10pm to 11pm, leaving on a single light or candle for this shared moment of reflection.”
The event will be complemented by a candlelit vigil held at Westminster Abbey.
Lights Out is one of a series of arts events marking the centenary of the war entitled 14-18 NOW. For further details, visit www.1418now.org.uk .