Will-o'-the-wisp

One possible naturalistic and scientific explanation for such phenomena is that the oxidation of hydrogen phosphide and methane gases produced by the decay of organic material may cause glowing lights to appear in the air. Experiments, for example, done by the Italian chemists Luigi Garlaschelli and Paolo Boschetti, have replicated the lights by adding chemicals to the gases formed by rotting compounds. Critics claim that this theory does not easily account for reported cases which claim lights bob, swoop, soar upwards or downwards, or move against the wind.

William Corliss writes, in Remarkable Luminous Phenomena in Nature (Sourcebook Project,[1] Glen Arm, MD, 2001:290): "No satisfactory mechanism has been demonstrated whereby gases escaping from marshy areas will spontaneously ignite. Furthermore, most low-level nocturnal lights are cold—not what one would expect from burning methane. Also, no one has explained how clouds of luminous gas can maintain size and shape while engaging in erratic maneuvers over many minutes."

Others believe bioluminescent effects (e.g. honey fungus) cause the light. Other explanations include causes similar to ball lightning.

More recently, under the broader banner of "Earth Lights," pseudoscientific theories as to how they are produced have been put forward by Professors Derr & Persinger, and Paul Devereux (who, in some circles, is considered the 'authority' on earth lights of various kinds, including ball lightning, St. Elmo's Fire and lights associated with earthquakes). Derr & Persinger put forward the theory that earth lights may be generated by tectonic strain. (These are faults in the earth's crust, including earthquake faults.) The theory goes that the strain causes heat in the rocks, vaporising the water in them. Piezoelectric rocks such as quartz then produce electricity, which is channeled up through this column of vaporised water, until it reaches the surface—somehow displaying itself in the form of earth lights. This theory would assert that the majority of earth lights are seen over places of tectonic strain. If it is correct, it would explain why such lights often behave in an erratic and even seemingly intelligent manner, often defying the laws of gravity. Paul Devereux's explanation, however, is much broader. He thinks that the link between the lights and the landscape is more tenuous. He says that they are probably related to many things: tectonic strain, weather conditions, local geography, 'ley lines', terrain, water table depth and so forth. This explanation, however, is rejected by most experts as highly unscientific.

Another theory was put forward claiming these lights are barn owls with luminescent plumage. Hence the possibility of them floating around, reacting to other lights, etc. See A Review of accounts of luminosity in Barn Owls Tyto alba.