Green light seen in space (9)
I believe the answer is:
clearance
I believe this clue is a double definition.
'green light' is the first definition.
(I've seen this in another clue)
'space' is the second definition.
(I know that clearance is a type of space)
'seen in' acts as a link.
(Other definitions for clearance that I've seen before include "Sanction" , "Headroom" , "Intervening space" , "Authority" , "Eviction from lands" .)