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