Light beams (4)
I believe the answer is:
rays
'light beams' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for rays that I've seen before include "Beams from sun or moon" , "we hope to catch occasionally out of the blue?" , "Single lines of light" , "Beams of sunlight" , "Narrow beams of light" .)