It is welcomed on the month of Karthigai in the Tamil calendar on a Karthigai Pournami (full moon). Traditionally, earthen lamps are lit in the evening after sunset.
This festival is believed to be the oldest festival celebrated by the Tamils as evidence from Tamil literature dating back to 2500 BC have written accounts of the Karthigai festival. Several other Tamil literature like the ‘’Agananuuru”, “Jeevakachintamani”, ''Karnarpadu'' from the Sangam period has also described this festival.
To stop this argument, Lord Shiva appeared in the form of a fire and challenged the two fighting Gods to find the end of the fire from the top and bottom. Lord Brahma took the form of a bird and tried to find the top of the fire, whereas, Lord Vishnu took the form of boar to find the bottom of the pillar.
Ancient kings later on built a temple on the hill as a commemoration to Lord Shiva. The temple is named Annamalaiyar Temple and the hill was named Annamalai Hill. Thousands of devotees flock to this temple in Thiruvannamalai to join the Karthigai Deepam because it is welcomed in a grand manner.
A huge light is lit at the Annamalaiyar Temple from around 5 pm on Karthigai Deepam. The locals belief that it will bring them closer to Lord Shiva. Lord Shiva is believed to shed all his blessing during this time of the year and devotees will pray to bring peace and end all the troubles in their everyday life.