After bungle, source of light is softened (7)
I believe the answer is:
muffled
'is softened' is the definition.
(synonyms)
'after bungle source of light' is the wordplay.
'after' says to put letters next to each other.
'bungle' becomes 'muff' (muff is a kind of bungle).
'source of light' becomes 'led' (abbreviation for light emitting diode).
'muff' next to 'led' is 'MUFFLED'.
(Other definitions for muffled that I've seen before include "Silenced; wrapped" , "Wrapped (up), stifled" , "Of sound, deadened or made indistinct" , "Wrapped for warmth" .)