Rear light's mentioned (5)
I believe the answer is:
raise
'rear' is the definition.
(I know that rear is a kind of raise)
'light's mentioned' is the wordplay.
'light's' becomes 'ray's' (ray is a kind of light).
'mentioned' indicates a 'sounds like' (homophone) clue.
'rays' is a homophone of 'RAISE'.
(Other definitions for raise that I've seen before include "More money from America" , "Make greater" , "Gather" , "climb" , "What a poker player might do" .)