Show a light (4)
I believe the answer is:
fair
I believe this clue is a double definition.
'show' is the first definition.
(fair is a kind of show)
'a light' is the second definition.
(I've seen this before)
(Other definitions for fair that I've seen before include "Favourable" , "Treating people equally" , "Free from discrimination" , "Impartial, so-so" , "Light; entertainment" .)