Green light in spare room (9)
I believe the answer is:
clearance
This clue is a double definition.
'green light' is the first definition.
(I've seen this in another clue)
'spare room' is the second definition.
(I've seen this before)
'in' acts as a link.
(Other definitions for clearance that I've seen before include "Official authorisation" , "Intervening space" , "Eviction from lands" , "Go-ahead" , "Vacation" .)