Dev Diwali 2021: Dev Diwali is celebrated on the full moon day after Kartik Amavasya. This time Dev Diwali will be celebrated on Friday, November 19, 2021. It is called Tripurari Purnima because in ancient times on this date Shiva killed a demon named Tripurasur. Apart from this, it is believed that Lord Vishnu had also taken Matsya avatar on Kartik Purnima. Sikh Guru Nanak Devji was also born on this day.