Source of Light Arts movement (4)
I believe the answer is:
star
'source of light' is the definition.
(thesaurus)
'arts movement' is the wordplay.
'movement' is an anagram indicator (letters move around).
'arts' anagrammed gives 'STAR'.
(Other definitions for star that I've seen before include "Public figure" , "huge body of gas?" , "Outstanding person" , "Brilliant performer?" , "Distant sun" .)