Ball lightning is an unexplained 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 accounts over the centuries, and have received much attention from scientists. 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.