Columns of light or heat (4)
I believe the answer is:
rays
'columns of light or heat' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for rays that I've seen before include "Columns of light or heat" , "Beams from sun or moon" , "Flat fish" , "Single lines of light" , "Pencils of light" .)