Light show (4)
I believe the answer is:
fair
I believe this clue is a double definition.
'light' is the first definition.
(I've seen this in another clue)
'show' is the second definition.
(I know that fair is a type of show)
(Other definitions for fair that I've seen before include "Market for the sale of produce" , "All clues should be" , "Free from bias" , "Sign following Pisces" , "Beautiful; exhibition" .)