Dev Deepavali is observed on the first day of the Margashirsh month as per the traditional calendar followed in
Maharashtra. Dev Deepavali 2015 date is December 12. It must be noted that Dev Deepavali is also observed on the Kartik Purnima day in many regions - this is on November 6.
Please note that in many regions Dev Diwali is observed on Kartik Purnima. That is around 15 days earlier.
Dev Deepavali as the name suggests is dedicated to the Devas or Demi Gods. It is observed to commemorate the victory over demons and their return to heaven or Devaloka.
The most popular dev Deepavali is the one observed during the Kartik Purnima day which is the first Purnima after the Diwali celebrations.