Bright in bar after opening of curtains (6)
I believe the answer is:
clever
'bright' is the definition.
(thesaurus)
'bar after opening of curtains' is the wordplay.
'bar' becomes 'lever' (lever is a kind of bar).
'after' means one lot of letters go next to another.
'opening of curtains' becomes 'c' (I am not sure about this - if you are sure you should believe this answer much more).
'lever' put after 'c' is 'CLEVER'.
'in' acts as a link.
(Other definitions for clever that I've seen before include "Quick-minded" , "Cute" , "Bright; smart" , "Smar and canny" , "Deft, able, bright" .)