According to the Hindu calendar, Kartik (Oct-Nov) is the celestial month especially on the banks of the Ganga in Varanasi. Millions of Diyas (earthen Lamps) illuminate the ghats (banks) amidst chanting of Vedic mantras.

Dev Deepavali is celebrated on the occasion of Kartik Poornima when the Ghats of Varanasi come alive with thousands of Diyas (earthen lamps). Dev Deepavali, celebrated on the fifteenth day of Diwali, is a tribute to river Ganga by the people of Varanasi. Dev Deepavali is held on the full moon day in the month of Kartik (also known as Kartik Purnima) and is observed with great fanfare and feasts. It is believed that on the day of Dev Deepavali, the Gods descend on Earth. It is interesting to note that the Kartik Purnima festival also coincides with the Jain light festival and Guru Nanak Jayanti.

To mark the occasion and also to showcase the cultural heritage of Varanasi, the Uttar Pradesh Tourism department organizes a four-day Ganga Mahotsav around this period. A large number of Hindu devotees start assembling from the day of the Prabodhini Ekadasi (the eleventh day of the fortnight) itself. The official celebration is usually held on the Dasaswamedh Ghat. On the occasion of the Ganga Mahotsava, reputed artists and performers from all over the country come and perform, making the celebrations more eventful.

On the eve of Kartik Purnima, the number of pilgrims begins to increase manifolds and most of the pilgrims camp by the riverside. In the evening, pilgrims and local people decorate the entire riverbank with tiny earthen lamps ('Diya'). These lamps are lit as a mark of welcome to the Gods as they descend on earth. The little sparks of fire flicker elegantly and is a wonderful sight to watch. The 'Ganga-Aarti' is an important event in the evening. Almost all Ghats organize their own ceremony. Huge lamps are set ablaze and the priest holds forth the lamp as the multitude chants the hymns.