Backlight outside good when darkness falls (5)
I believe the answer is:
night
'falls' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for night that I've seen before include "From dusk until dawn" , "See 8" , "Hours of darkness" , "Sunset to sunrise" , "'The 2 8 of the dog in the _____'" .)