The answer to this clue should fit the light (7)
I believe the answer is:
glazier
'the answer to this clue should fit the light' is the definition.
(a glazier fits windows - 'light' can mean a window)
This is all the clue.
(Other definitions for glazier that I've seen before include "Glass cutter" , "Person who cuts flat glass to size" , "Window repairer" , "Window mender" , "Window fitter" .)