Earthquake Lights are lights that appear in the sky during, after, and occasionally before an earthquake, especially severe ones.  They resemble the aurora Borealis, or northern lights.  Scientists had no explanation for this phenomena so most have simply denied that it happens, dismissing them as electrical power transformers arching, etc.  
    This phenomena has a long history.  The Greeks reported in 373 BC that "immense columns of flame" foretold a great earthquake.  The night before the tangshan earthquake in 1976 many area residents saw strange lights in the sky.  During the 2007 earthquake in Peru the lights were reported.  They were also reported during the Quebec quakes in 1988 and 1989 and the 1999 quake in Japan.  The first photographs of them were taken in Japan in the 1960s during a month long swarm of quakes.  The best evidence of them come from the recent earthquake in China.  Someone managed to video them with a cell phone 30 minutes before the earthquake occurred.  Some Scientists believe that this video shows a very different phenomena: rainbows caused by ice crystals, but how strange that these rainbows happened to appear just before a major earthquake and in the area where the quake happened.  
    Theories are now popping up to explain the lights.  One theory is that gases released from the earth become electrically charged.  Another is that the earths magnetic field is disturbed in the area by the great tectonic stress.    The best theory so far is from physicist Friedemann Freund who noted  that rock can contain positive charged areas called p-holes andd p-holes are good conductors.  He conducted experiments using sensors that detected electrical discharge, radio noise and light released by impacted rock.  
    It is hoped that the lights will help in warning people of pending eathquakes, but at this point not enough is known.  They may not appear at all, they may appear only during a quake or they may appear before the quake.  When they do appear before a quake, they have been seen anywhere from a few minutes to several day before the quake occured.  Nonetheless, I think it is worthwhile to let people know about this and warm them of what it likely means if they do see these lights.