Irishman, I have to disagree with you there. It's a confusing topic, but from what I can gather "earthquake lights" are a completely different phenomenon which has not been proven, and may have a very mundane explanation.
http://en.wikipedia.org/wiki/Earthquake_light

All of the photographs and videos of purported earthquake lights show a glow on the horizon which is visible at night(and which would likely be invisible in daylight). Quite different from a circumhorizontal arc. Here's a citation link from the Wikipedia article, which has a collection of videos and stills. To me these seem pretty unconvincing, and I would guess what's shown in the the urban videos are caused by power surges.
http://inamidst.com/lights/earthquake

Another thing you shouldn't confuse this with is what's called "earthquake clouds". That's a term used by people who claim to be able to predict earthquakes weeks in advance by observing the shape of clouds.
http://en.wikipedia.org/wiki/Earthquake_cloud

As for the idea that circumhorizontal arcs can predict earthquakes. . . I guess it would need to happen more then once.