Sydney Morning Herald: IT IS one of the world’s most recognised buildings but its distinctive sails are now often left in the dark. In a move expected to save about 15 tonnes of greenhouse gases every year, the Sydney Opera House is switching off its external floodlights at 2am on weekends, and am on weekdays. The Opera House briefly extinguished its sail lights for the first Earth Hour in 2007, did it again last year, and will do so once more on the evening of March 28. But the ghostly vista …