A policeman stands guard as a lantern is placed at the front door of Number 10 Downing Street during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War 1. Picture: Dylan Martinez
A policeman stands guard as a lantern is placed at the front door of Number 10 Downing Street during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War 1. Picture: Dylan Martinez
People enjoy an artwork entitled "Spectra" by Japanese visual artist Ryoji Ikeda during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War 1 in London. Picture: Dylan Martinez
People enjoy an artwork entitled "Spectra" by Japanese visual artist Ryoji Ikeda during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War 1 in London. Picture: Dylan Martinez
A roll of honour for fallen soldiers is seen as the Piccadilly lights are switched off for an hour to mark the 100th anniversary of the outbreak of World War 1, at Piccadilly Circus in London. Picture: Paul Hackett
A roll of honour for fallen soldiers is seen as the Piccadilly lights are switched off for an hour to mark the 100th anniversary of the outbreak of World War 1, at Piccadilly Circus in London. Picture: Paul Hackett
A couple embrace as a roll of honour for fallen soldiers is displayed after lights are switched off for an hour to mark the 100th anniversary of the outbreak of World War 1, at Piccadilly Circus in London. Picture: Paul Hackett
A couple embrace as a roll of honour for fallen soldiers is displayed after lights are switched off for an hour to mark the 100th anniversary of the outbreak of World War 1, at Piccadilly Circus in London. Picture: Paul Hackett
The Duchess of Cornwall (centre) accompanied by Dean of Westminster the Reverend John Hall (right) walks by the Tomb of Unknown Warriors as she attends a vigil and prayer service at Westminster Abbey in London. Picture: Sang Tan
The Duchess of Cornwall (centre) accompanied by Dean of Westminster the Reverend John Hall (right) walks by the Tomb of Unknown Warriors as she attends a vigil and prayer service at Westminster Abbey in London. Picture: Sang Tan
Catherine, the Duchess of Cambridge, King Philippe of Belgium, British Prime Minister David Cameron and Prince William, the Duke of Cambridge, pay their respects at St Symphorien Military Cemetery in Mons. Picture: Chris Jackson
Catherine, the Duchess of Cambridge, King Philippe of Belgium, British Prime Minister David Cameron and Prince William, the Duke of Cambridge, pay their respects at St Symphorien Military Cemetery in Mons. Picture: Chris Jackson
A lantern is placed at the front door of Number 10 Downing Street during "Lights Out",  as part of commemorations to mark the 100th anniversary of the outbreak of World War 1 in London. Picture: Dylan Martinez
A lantern is placed at the front door of Number 10 Downing Street during "Lights Out", as part of commemorations to mark the 100th anniversary of the outbreak of World War 1 in London. Picture: Dylan Martinez
Catherine, the Duchess of Cambridge, attends a ceremony at St Symphorien Military Cemetery in Mons, Belgium. Picture: Francois Lenoir
Catherine, the Duchess of Cambridge, attends a ceremony at St Symphorien Military Cemetery in Mons, Belgium. Picture: Francois Lenoir
(From left to right) Britain's Catherine, Duchess of Cambridge, Belgium's Queen Mathilde, Belgium's King Philippe, Britain's Prime Minister David Cameron and Britain's Prince William attend a ceremony at St Symphorien Military Cemetery in Mons. Picture: Francois Lenoir
(From left to right) Britain's Catherine, Duchess of Cambridge, Belgium's Queen Mathilde, Belgium's King Philippe, Britain's Prime Minister David Cameron and Britain's Prince William attend a ceremony at St Symphorien Military Cemetery in Mons. Picture: Francois Lenoir
British Major Maurice French, 84, of Heytesbury in Wiltshire, stands in front of his uncle's grave during a commemoration ceremony to mark the 100th anniversary of the outbreak of World War 1. Picture: Virginia Mayo
British Major Maurice French, 84, of Heytesbury in Wiltshire, stands in front of his uncle's grave during a commemoration ceremony to mark the 100th anniversary of the outbreak of World War 1. Picture: Virginia Mayo
Belgium's King Philippe, left, and Britain's Prince William attend a ceremony at St Symphorien Military Cemetery in Mons. Picture: Francois Lenoir
Belgium's King Philippe, left, and Britain's Prince William attend a ceremony at St Symphorien Military Cemetery in Mons. Picture: Francois Lenoir
(L-R) Britain's Prince William, Catherine, Duchess of Cambridge and Prince Harry attend a ceremony at the St Symphorien Military Cemetery in Mons. Picture: Gareth Fuller/Pool
(L-R) Britain's Prince William, Catherine, Duchess of Cambridge and Prince Harry attend a ceremony at the St Symphorien Military Cemetery in Mons. Picture: Gareth Fuller/Pool
Britain's Prince Harry speaks with cadets during a "Step Short" ceremony to mark the 100th anniversary of the outbreak of World War 1 in Folkestone, in southern England. Picture: Luke MacGregor
Britain's Prince Harry speaks with cadets during a "Step Short" ceremony to mark the 100th anniversary of the outbreak of World War 1 in Folkestone, in southern England. Picture: Luke MacGregor
Belgium's King Philippe (back left) attends a ceremony at the Cointe Inter-allied Memorial to commemorate the 100th anniversary of the outbreak of World War 1. Picture: Yves Herman
Belgium's King Philippe (back left) attends a ceremony at the Cointe Inter-allied Memorial to commemorate the 100th anniversary of the outbreak of World War 1. Picture: Yves Herman
Light is beamed into the sky from Trafalgar Square to mark the100th anniversary of the outbreak of World War 1, in London. Picture: Paul Hackett
Light is beamed into the sky from Trafalgar Square to mark the100th anniversary of the outbreak of World War 1, in London. Picture: Paul Hackett

Lights across Britain switched off for an hour on Monday night in a tribute to the dead of World War 1 inspired by the prophetic observation of Britain's foreign minister on the eve of war 100 years ago.

“The lamps are going out all over Europe,” Edward Grey told an acquaintance, shortly before Britain declared war on Germany on August 4, 1914. “We shall not see them lit again in our lifetime.”