Depict a red light (7)
I believe the answer is:
portray
'depict' is the definition.
(I know that depict can be written as portray)
'a red light' is the wordplay.
'a red' becomes 'port' (I am not sure about this - if you are sure you should believe this answer much more).
'light' becomes 'ray' (ray is a kind of light).
'port'+'ray'='PORTRAY'
Can you help me to learn more?
(Other definitions for portray that I've seen before include "Use words to describe" , "sketch" , "Describe in words or make a picture" , "Act" , "Delineate" .)