Strike a light! (4)
I believe the answer is:
lamp
This clue is a double definition.
'strike' is the first definition.
(lamp can mean to hit or strike)
'a light' is the second definition.
(lamp is a kind of light)
(Other definitions for lamp that I've seen before include "Source of artificial light" , "Artificial source of illumination" , "Florence Nightingale was the Lady with the . . . ." , "Table light" , "Source of light, usually portable" .)