Hutasani Poornima, or Hutashani Purnima, is the full moon day in the month of Falgun or Phalguna (February – March) in traditional lunar Hindu calendar. In 2017, the date of Hutasani Purnima is March 12. It is also known as Hutasani Fagun Sud Poonam. The famous Holika Dahan associated with Holi festival is observed on the Hutasani Purnima day.
According to Puranas, the great demon king Hiranyakashipu, with the help of a boon from Brahma, ruled the three worlds and forcefully made all the people worship him. But he could not make Prahlad, his son, worship him. Prahlad was an ardent devotee of Lord Vishnu.
Hiranyakashipu could not tolerate his son worshipping Lord Vishnu and looked for ways to eliminate him. But each time the young Prahlad was rescued by Lord Vishnu. Finally, the task of annihilating Prahlad was given to Holika, a sister of Hiranyakashipu. She had a boon that she would never get burnt by fire.
Taking advantage of this boon, Holika took Prahlad and sat in a burning pyre. But with the blessings of Lord Agni and Vishnu, Prahlad escaped without any injuries. But Holika got burnt and was killed.
People light up bonfire in memory of this incident on the day before Rang Holi. It symbolically represents the victory of good over evil. In some regions, it is believed that Lord Agni saved Prahlad and people lit bonfire to worship him.