Streak photograph of lightning. The electrified cumulonimbus cloud (the thunderstorm) is simply a giant natural electrical capacitor. The "light" in lightning is generated by the positive electron flow in the return stroke. If the cloud has created enough voltage, several return strokes will be necessary to equalize the charges between the negatively charged cloud base and the positively charged ground. In this photograph the camera was moved horizontally while mounted on a tripod during a lightning strike. The camera recorded thirteen (13) return strokes.