Ball lightning refers to mobile bright spheres sometimes observed during thunderstorms. Most observations of ball lightning are made during thunderstorm activity, within a few feet of the ground. A typical ball lightning is about as big as an orange or grapefruit, and lasts a few seconds. Visual sightings are often accompanied by sound, odor, and permanent material damage.
Very similar, if not identical phenomena, occur in submarines due to electric discharge of direct current across a circuit breaker, and in high-power electrical equipment. Ball lightning is sometimes confused with St Elmo's Fire. St Elmo's fire is a corona discharge from a pointed conducting object, which must remain attached to a conductor, and which usually lasts much longer than ball lightning.