A soft light, please (4)
I believe the answer is:
pray
'please' is the definition.
(I've seen this before)
'a soft light' is the wordplay.
'a soft' becomes 'p' (musical abbreviation for 'piano').
'light' becomes 'ray' (ray is a kind of light).
'p'+'ray'='PRAY'
(Other definitions for pray that I've seen before include "Address a deity" , "make supplications" , "Appeal to higher authority" , "Devoutly hope" , "May I ask" .)