Lack of light (7)
'lack of light' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for dimness that I've seen before include "exhibiting stupidity" , "Shortage of light; weakness of intellect" , "That's not very clever" , "Dark" , "Quality of dull light" .)
'lack of light' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for darkness that I've seen before include "Unlit state" , "Black of night" , "See 19" , "Gloom" , "Better to light a candle than to curse it, they say" .)