Many lights used in the theatre (6)
I believe the answer is:
clamps
'in the theatre' is the definition.
I can't judge whether this definition defines the answer.
'many lights' is the wordplay.
'many' becomes 'c' (C is the Roman numeral for 100).
'lights' becomes 'lamps' (lamp is a kind of light).
'c'+'lamps'='CLAMPS'
'used' acts as a link.
Can you help me to learn more?
(Other definitions for clamps that I've seen before include "fasteners" , "Devices to hold things, car wheels say" , "Devices to hold things firmly, car-wheels say" , "Holds tightly with device - illegally parked cars? (6)" , "Grips" .)