Diwali, known as Deepavali, in South India is celebrated a day before the Diwali day in
North India. The difference of dates is primarily due to the variations in the regional calendars. In 2014, the date of Deepavali in Tamil Nadu, Karnataka, Kerala and in some parts of Andhra Pradesh is on October 22. In North India, Diwali is on October 23.
In Tamil Nadu, Karnataka and parts of Andhra Pradesh, Deepavali is celebrated to commemorate the killing of the demon Narakasura by Lord Krishna. This is observed on Krishna Paksha Chaturdasi mostly a day before Diwali in North India.
In Kerala, Deepavali is a low-key affair and is believed to be the day Lord Ram returned from exile.
In Karnataka, the day after Deepavali is observed as Bali Paadyami to mark the day of King Bali's return to his subject once a year.
There may be difference in date and reason for Deepavali but the central theme – good wins over evil, remains the same.