Overview
Dev Deepawali, literally the "Diwali of the Gods" or "Festival of Lights of the Gods", is a festival celebrated in the city of Varanasi, Uttar Pradesh, on Kartik Poornima, the full moon of the Hindu month of Kartika (November–December). It falls fifteen days after Diwali and is also observed as Tripura Purnima Snan.
On this occasion, the steps of all the ghats along the Ganges riverfront in Varanasi, stretching from Ravidas Ghat at the southern end to Rajghat, are illuminated with more than a million earthen lamps (diyas). The lighting is offered in honour of the river Ganges and its presiding goddess, Ganga. According to traditional belief, the gods are said to descend to earth on this day to bathe in the sacred waters of the Ganges.
The tradition of lighting lamps along the ghats on Dev Deepawali was first initiated at the Dashashwamedh Ghat by Pandit Kishori Raman Dubey, popularly known as Babu Maharaj, in 1991. The practice has since grown into a widely observed festival drawing residents and visitors to the riverfront.
During the festival, houses are decorated with oil lamps and coloured designs on their front doors. Processions carrying decorated images of deities are taken out through the streets of Varanasi, and oil lamps are set afloat on the river as part of the celebrations.
References
Adapted from the English Wikipedia article on Dev Deepavali (Varanasi).