Dark close, light's ending (5)
I believe the answer is:
night
'dark' is the definition.
(it's dark at nighttime)
'close light's ending' is the wordplay.
'close' becomes 'nigh' (similar in meaning).
'ending' says to take the final letters (the letter at the end of the word).
The last letter of 'light' is 't'.
'nigh'+'t'='NIGHT'
(Other definitions for night that I've seen before include "The dark time" , "From dusk until dawn" , "late" , "''Twas the ... before Christmas, when all through the house / Not a creature was stirring, not even a mouse''" , "death" .)