Karthikai Deepam is a festival of lights celebrated by Tamil Hindus on the full moon day of Karthikai month.
This occurs on the day when the moon is in conjunction with the constellation Karthigai (Pleiades) and purnima.
Karthigai festival in Tiruvannamalai hills is very famous. On Karthigai day, a huge fire lamp is lit up on the hill, visible for several kilometers around the hill.
Web : http://en.wikipedia.org/wiki/Karthikai_Deepam