This year the first three days of the 17 day Deepam Festival started off last night (November 30, 2016) at the Durga Amman Temple, Tiruvannamalai. The reason for the unique connection with the Goddess at Durga Amman Temple with the Karthigai Festival is believed to be because of the Goddess and her fight with the demon Mahisha. Go to this link to read ‘The Fight with Mahisasura’.
In the Mahishasura legend, before fighting with the demon, the Goddess appointed four noble Bhairavis (celestial damsels) to keep watch on all four sides of Arunagiri.
"Admit only those who have come to worship Arunachala and are tired, hungry and thirsty. Others should not enter. She then appointed strong men to guard the boundaries of Arunachala and continued Her penance at Her ashram."
[The Glory of Arunachala]
In accordance with the mythology of Arunachala, Durga is recognised as Guardian of Arunachala and thus a precursor of the Deepam Festival is always a celebration of this aspect of the Goddess.