What are earthquake lights?

Phenomena such as sheet lightning, balls of light, streamers, and steady glows, reported in association with earthquakes are called earthquake lights (EQL). Geophysicists differ on the extent to which they think that individual reports of unusual lighting near the time and epicenter of an earthquake actually represent EQL: some doubt that any of the reports constitute solid evidence for EQL, whereas others think that at least some reports plausibly correspond to EQL. Physics-based hypotheses have been proposed to explain specific classes of EQL reports, such as those in the immediate vicinity of the causative fault at the time of a major earthquake. On the other hand, some reports of EQL have turned out to be associated with electricity arcing from the power lines shaking.