Bad lighting (5)
I believe the answer is:
arson
'bad lighting' is the definition.
The answer and definition can be both acts as well as being singular nouns.
Maybe they are linked in a way I don't understand?
This is all the clue.
Can you help me to learn more?
(Other definitions for arson that I've seen before include "Fire-raising crime" , "Criminal activity" , "Malicious burning to destroy property" , "Crime involving fire" , "Act of a pyromaniac" .)