Light pollution finally stops after November (7)
I believe the answer is:
lantern
'light' is the definition.
(lantern is a type of light)
'pollution finally stops after november' is the wordplay.
'finally' indicates one should take the final letters.
'stops' means one lot of letters goes inside another (stopping can mean blocking a gap).
'after' becomes 'later' (I've seen this before).
'november' becomes 'N' (phonetic alphabet: alpha, bravo, charlie etc.).
The final letter of 'pollution' is 'n'.
'n' placed inside 'later' is 'lanter'.
'lanter'+'n'='LANTERN'
(Other definitions for lantern that I've seen before include "Light-admitting structure on roof" , "Enclosed light" , "Case for a light, provides pictures when magic" , "Enclosed lamp" , "Light held by 26/27 Across" .)