Arizona. Lightning. Time exposure image of lightning strikes over Tucson, Arizona, USA..The silhouette of a giant saguaro cactus (Carnegiea gigantea) is in the foreground at right and left. Car tail light trails are also seen in the foreground. Lightning occurs when a large electrical charge builds up in a cloud, probably due to the friction of water and ice particles. The charge induces an opposite charge on the ground, and a few leader electrons travel to the ground. When one makes contact, there is a huge backflow of energy up the path of the electron. This produces a bright flash of light, and temperatures of up to 30,000 degrees Celsius. Photographed in Tucson, Arizona, USA. .