The Emirates Stadium is a three-tiered bowl with translucent polycarbonate roofing over the stands but not over the pitch.[78] The underside is clad with metallic panels and the roof is supported by four triangular trusses, made of welded tubular steel.[78] Two trusses span 200 metres (660 ft) in a north–south direction while a further two span an east–west direction.[78] The trusses are supported by the stadium's vertical concrete cores, eight of which connected to them by steel tripods. They in turn each house four stairways, a passenger lift as well as service access.[78] Façades are either glazed or woven between the cores which allows visitors on the podium to see inside the stadium.[78] The glass and steel construction was devised by Populous to give an impression that the stadium sparkles in sunlight and glows in the night.