The idea behind this festival is to keep away bad things from life and welcome the good and holy things of life that’s why it is called the festival of lamps. We use to light oil lamps all over the house in the evening and crackers, fires are burnt. Rows of Agal vilakkus (Clay Oil lamps) are lit in every house. Karthigai is essentially a festival of lamps. The lighted lamp is considered an auspicious symbol. It is believed to ward off evil forces and usher in prosperity and joy.
While the lighted lamp is important for all Hindu rituals and festivals, it is indispensable for Karthigai. This festival is also celebrated to commemorate the bonding between brothers and sisters in south India (analogous to Bhaiya-Dhuj and Raakhi). Sisters pray for the prosperity and success of their brothers and light lamps to mark the occasion.
In Telugu households, Kaartheeka maasam (month) is considered very auspicious. The Kartheeka month starts on the day of Deepawali. From that day till the end of the month, oil lamps are lit every day. On Kartheeka Pournami (full moon of Kartheeka month) oil lamp with 365 wicks, prepared at home, are lit in Lord Shiva temples. Apart from that, Kaartheeka puranam is read and fasting is observed till sunset, every day for the whole month.