This festival is considered as the extension of the Deepavali festival. In the olden days, the people used to double the number of lamps every day from the day of Deepavali and this way, they end up with a number of lamps on the day of Karthigai Deepam.
Karthigai Deepam is the oldest festival celebrated by Tamils. Evidence from Tamil literature lets us know that this festival is one of the oldest. The oldest available Tamil Literature is Tolkappiyam dating back to 2500 BC and this Tholkappiyam gives a concise account of Karthigai festival.
Other Tamil Literatures like “Agananuuru”, “Jeevakachintamani” , ‘Karnarpadu’, ‘Kalavazhi Narpadu’ etc. of the Sangam period also carry vivid description of this festival. In “Karnarpadu”, the poet describes how in the Tamil month of Karthigai, the lamps lit by people blossomed on earth, bringing rain in its wake.
On this day, people clean their houses and draw ‘Kolams’ (Rangoli) in front of the house and also place some lamps on it. First, they place the lamps in the puja room and light them. After the ‘Deeparadhana’ the lamps are moved to the different locations in the house including on the streets. Thus the lamps lit by all houses glow all over the streets.
In commemoration of this festival, at the sunset time, there would be Deeparadhana and Maha Aarti in all Temples followed by Bonfire in front of the Temple.