Hindu festival of lights (6)
I believe the answer is:
diwali
'hindu festival of lights' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for diwali that I've seen before include "religious festival" , "Hindu festival; I'd wail (anag.)" , "Light festival" , "Indian festival" , "Hindu festival of lights" .)