Ray and Ben with a sum that's wrong (7)
I believe the answer is:
sunbeam
'ray' is the definition.
(I know that sunbeam is a type of ray)
'ben with a sum that's wrong' is the wordplay.
'with' means one lot of letters go next to another.
'that's wrong' is an anagram indicator.
'a'+'sum'='asum'
'ben' put after 'asum' is 'asumben'.
'asumben' anagrammed gives 'SUNBEAM'.
'and' is the link.
(Other definitions for sunbeam that I've seen before include "Bright shaft of daylight" , "sheds a bit of light" , "Ray of natural light" , "Ray of solar light" , "Bright ray -- bus name (anag)" .)