Ball lightning is an unexplained atmospheric electrical phenomenon described as luminescent, spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms, the phenomenon is said to last considerably longer than the split-second flash of a lightning bolt. Some nineteenth century reports describe balls that eventually explode and leave behind an odor of sulfur. Descriptions of ball lightning appear in a variety of anecdotes over the centuries, but most scientists have treated reports of ball lightning skeptically. An optical spectrum of what appears to have been a ball-lightning event was published in January 2014, and included a video at high frame-rate. Laboratory experiments have produced effects that are visually similar to reports of ball lightning, but how these relate to the supposed phenomenon remains unclear.
Scientists have proposed a number of hypotheses to explain reports of ball lightning over the centuries, but scientific data on ball lightning remains scarce. The presumption of its existence has depended on reported public sightings which have produced somewhat inconsistent findings. Owing to inconsistencies and to the lack of reliable data, the existence of ball lightning as a phenomenon remains unproven.