Secure light (4)
I believe the answer is:
land
I believe this clue is a double definition.
'secure' is the first definition.
(I've seen this in other clues)
'light' is the second definition.
(I've seen this before)
(Other definitions for land that I've seen before include "soil" , "Acquire" , "nation" , "Put in" , "SECOND PART OF 15" .)