Ray perhaps is small and perversely heavy (8)
I believe the answer is:
sunlight
'ray perhaps' is the definition.
(ray of light)
'small and perversely heavy' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'and' is a charade indicator (letters next to each other).
'perversely heavy' becomes 'unlight' (heavy is the opposite of light).
's'+'unlight'='SUNLIGHT'
'is' is the link.
(Other definitions for sunlight that I've seen before include "Possible reason why blinking" , "Hustling under heavenly radiance" , "Beams" , "Solar illumination" , "Prerequisite for photosynthesis" .)