An earthquake light is an unusual luminous aerial phenomenon that reportedly appears in the sky at or near areas of tectonic stress,seismic activity, or volcanic eruptions. Once commonly challenged, it was not until photographs were taken during the Matsushiro earthquake swarm in Nagano, Japan, from 1965 through 1967, that the seismology community acknowledged their occurrence.
The lights are reported to appear while an earthquake is occurring, although there are reports of lights before or after earthquakes, such as reports concerning the 1975 Kalapana earthquake. They are reported to have shapes similar to those of the auroras, with a white to bluish hue, but occasionally they have been reported having a wider color spectrum. The luminosity is reported to be visible for several seconds, but has also been reported to last for tens of minutes. Accounts of viewable distance from the epicenter varies, in the 1930 Idu earthquake, lights were reported up to 70 miles from the epicenter. Earthquake lights were reportedly spotted in Tianshui, Gansu, approximately 400 km north-northeast of the earthquakes epicenter. The phenomenon was also widely observed and caught on film during the 2007 Peru, 2008 Sichuan, 2009 L’Aquila, 2010 Chile earthquakes, and on the 7th April 2011 filmed in Tokyo during the 7.1 magnitude earthquake on the East coast of Honshu, Japan. The phenomenon was also reported around the Aimuri Earthquake in New Zealand, that occurred 1 September 1888. The lights were visible in the morning of 1 September in Reefton, and again on the 8th of September. A more recent citing, as of April of 2011, occurred when a 7.0 earthquake struck Tokyo, Japan close to midnight on April 7th, 2011. The phenomenon can be clearly observed in news footage reporting the quake taken by the Japanese network, NHK. 
Earthquake lights are caused by an unknown mechanism. There are numerous theories as to how and why they occur.
Another possible explanation is local disruption of the Earth’s magnetic field and/or ionosphere in the region of tectonic stress, resulting in the observed glow effects either from ionospheric radiative recombination at lower altitudes and greater atmospheric pressure or as aurora. However, the effect is clearly not pronounced or notably observed at all earthquake events and is yet to be directly experimentally verified.
There is also debate in the scientific community regarding radon as a possible precursor to some earthquakes, so another theory is that glowing clouds might be light emission produced by ionization or plasma-chemical reactions