The snow-covered Olympic Stadium has sparkled under floodlights for the first time.
Prime Minister David Cameron, accompanied by a choir of local schoolchildren, hit the button for the big switch-on which shone a megawatt of light on to the showpiece venue.
It was the first time that all 532 bulbs had been lit together - in a scene that will be repeated during the London 2012 Games.
Mr Cameron joked that the £537 million stadium in Stratford, east London, looked more like a winter Olympic venue with ski-jumper Eddie the Eagle expected at any moment rather than the setting for the London 2012 summer Games.
But he told the 400-strong invited crowd, which included 2012 builders at the site: "It is being delivered on time and on budget thanks to British genius and many of the people here."
Introductions were carried out by London Mayor Boris Johnson, who did not seem aware that the lights take up to eight minutes to reach full power.
"They are coming, they are coming," Mr Johnson told the crowd before all the lights had phased in.
He described it as a "wonderful and historic evening", while also joking that with plans so advanced, including 75% of building work complete, London 2012 might consider holding a snap Olympics now 17 months before the Games "to catch the world napping".
There are 14 lighting towers reaching 70 metres (230ft) above the sports area. They are supporting a total of 532 individual lights.
Mr Cameron also spoke of changes to unpopular plans to cut £162 million from school sport.
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