Nonsense! Light up! (4)
I believe the answer is:
rats
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for rats that I've seen before include "Treacherous rodents" , "Blast" , "Rodent pests" , "Damn" , "(Hunts) rodents - expression of irritation" .)