A vice securing top of rotating light (3,4)
I believe the answer is:
arc lamp
'light' is the definition.
(arc lamp is a kind of light)
'a vice securing top of rotating' is the wordplay.
'vice' becomes 'clamp' (I've seen this in other clues).
'securing' indicates putting letters inside.
'top of' indicates taking the first letters.
The initial letter of 'rotating' is 'r'.
'a'+'clamp'='aclamp'
'aclamp' going around 'r' is 'ARC-LAMP'.
(Other definitions for arc lamp that I've seen before include "Electric light source" , "Intense illuminator" , "one of the bright lights" , "Source of bright light" .)