Karthigai Deepam Festival falls on the Sunday November 17, 2013, in Thiruvannamalai. November 17th  and the beginning of the Tamil month Karthigai fall on the same day.

Last year, Karthigai Deepam was celebrated on 27th November 2012

Pancharatra Deepam
Pancharatra Deeepam (also as Vishnu Deepam) is the festival of lights that is celebrated in Tamil Nadu. It is observed on the full moon day (or a day earlier) in the month of Karthigai (November-December) on the Karthigai Nakshatram (star) day. This Pancharatra Deepam ritual is followed by the Vaishanva Community and this year falls on 17th NOvember 2013.

Also see this:
Thirukarthigai Festival – Why Do We Celebrate Karthigai Deepam Kathigai Deepam Recipes