Light, soft drink (4)
I believe the answer is:
pale
'light' is the definition.
('pale' can be similar in meaning to 'light')
'soft drink' is the wordplay.
'soft' becomes 'p' (musical abbreviation for 'piano'**).
'drink' becomes 'ale' (ale is a kind of drink).
'p'+'ale'='PALE'
(Other definitions for pale that I've seen before include "stick" , "picket" , "Lightly coloured" , "Very light coloured" , "Dim - wan" .)