Broken down bus means travelling light (8)
I believe the answer is:
sunbeams
'travelling light' is the definition.
(beams of light travelling from a source)
'broken down bus means' is the wordplay.
'broken down' is an anagram indicator.
'bus'+'means'='busmeans'
'busmeans' anagrammed gives 'SUNBEAMS'.
(Other definitions for sunbeams that I've seen before include "daylight?" , "They provide light" .)