Ultra high-speed footage of the formation of a lightning bolt. At top right, several leaders are seen, forming short glowing channels of ionised air. These grow downwards until one contacts the ground, which allows a huge return stroke of current to pass up the ionised channel. This is the bolt that is seen as lightning. Electric charge can pass several times through the same channel once it is established, which gives lightning a flickering look when seen in real time. This footage was shot at 11, 852 frames per second, slowing the action down nearly 400 times. Filmed in the USA on a spring afternoon.