Left before light show (7)
I believe the answer is:
portray
'show' is the definition.
(to portray is to show or depict)
'left before light' is the wordplay.
'left' becomes 'port' (left side of a ship - opposite of starboard).
'before' is a charade indicator (letters next to each other).
'light' becomes 'ray' (ray is a kind of light).
'port'+'ray'='PORTRAY'
(Other definitions for portray that I've seen before include "Use words to describe" , "Delineate" , "Depict, present" , "Act" , "sketch" .)