Dev Deepawali is a famous Utsav celebrated every year at the holy city Varanasi. Dev Deepawali, which is also spelt as Dev Diwali, is celebrated to mark the victory of Lord Shiva over demon Tripurasur (त्रिपुरासुर). Hence Dev Deepawali Utsav is also known as Tripurotsav or Tripurari Purnima which is observed on the auspicious day of Kartik Purnima.
On Dev Deepawali, devotees take a holy dip in the Ganges on the auspicious day of Kartik Purnima and light earthen lamps or Diya(s) in the evening. When the dusk sets, the steps of all the Ghats on the riverfront of the Ganges are lit with millions of earthen lamps. Not only the Ghats of Ganges but also all temples of Benares are lit with millions of Diya(s).