"Earth lights" may be related to ball lightning and earthquake lights but do not require electrical storm or earthquake conditions in order to appear. They usually haunt localised regions and are terrain-related. In some places many have been seen for generations. These places have so far been found to contain recurring geological characteristics such as significant faulting, seismic history, mineral deposits or bodies of water. This apparent geological connection is further highlighted by old mining texts which tell of the use of lightballs emerging from the ground in prospecting for mineral seams, especially copper veins. This method of prospecting was used in England until early this century.
Prime amongst current theories accounting for the lights is the Tectonic Stress Theory which posits that a strain field is produced during tectonic flexing of the Earth's crust in suitable zones, not necessarily leading to earthquake or tremor, and that this generalised field can move through an area, causing electrical and geomagnetic changes and focusing in certain topographical and geological configurations, producing light phenomena.
Ethnology reveals that earth lights have been seen and absorbed into their magical worldview by many ancient cultures and are/were usually interpreted as various kinds of spirits or shamans flying at night. Light phenomena have been associated with many "holy" mountains and hills world-wide, and temples have even been built dedicated to the lights in India, China and the Alps. It may be that prehistoric standing stones in western Europe were likewise raised in honour of places haunted by light phenomena.
There have been many interpretations of the lights in Western society over the centuries. The longest-lived was that they were the fiery breath of dragons: the matter was the subject of scholarly debate during the Middle Ages. In Denmark and Germany, particularly strange lights were known as "treasure lights", hovering over buried treasure. In recent times they have been seen as enemy airships, and in World War Two, "foo fighters". Now they have been caught up in the UFO interpretation, though in some areas they are sometimes seen as ghosts or "spooklights".
Typically the lights appear as "basketball-sized" globes, but smaller and larger ones have also been reliably reported. Also, the lights can take on many shapes and can hover, fly rapidly, perform acrobatic manoeuvres, merge together, etc. The lights have been photographed, by individual witnesses and by research teams. The nature of the light energy is not known, but it seems to have electromagnetic aspects.
There are, however, more exotic reported characteristics of these phenomena: their ability to assume coherent shapes, as well as to shape-shift, is not understood (as is indeed the case with ball lightning): the lights can sometimes be seen from one direction, but not from another; they can sometimes exhibit rapidly alternating signs of having mass and being weightless; they can sometimes burn vegetation and witnesses yet at other times have no effect. They may represent some kind of "macro-quantum" effect occurring in nature.