Go out when you light up (6)
I believe the answer is:
strike
'go out' is the definition.
(thesaurus)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for strike that I've seen before include "Deliver a blow" , "Sudden attack; chime" , "Walk-out" , "Downing of tools" , "Agree on" .)