British Prime Minister David Cameron had asked Britons to switch off all but a single light in their homes for an hour
The last remaining light was extinguished at the Grave of the Unknown Warrior at 11pm, marking the exact time the British Empire joined the warEdward Grey (left) said: 'The lamps are going out all over Europe. We shall not see them lit again in our lifetime.'Grey's prophecy was also at the centre of a service in London's Westminster Abbey, where candles went out one by one
Piccadilly Circus displayed memorial images as the lights were turned offThe lights were also turned off on the London EyeThe Menin Gate Memorial in Belgium in near darkness after the lights that normally illuminate it were turned offBritish landmarks, including the Houses of Parliament, went dark from 10pm to mark the centenary of the start of the Great War
