Ray of light with doctor on right track (8)
I believe the answer is:
moonbeam
'ray of light' is the definition.
(moonbeam is a kind of ray of light)
'with doctor on right track' is the wordplay.
'with' is a charade indicator (letters next to each other).
'doctor' becomes 'mo' (medical officer).
'right track' becomes 'beam' (I can't explain this - if you can you should give a lot more credence to this answer).
'mo' next to 'on' is 'moon'.
'moon'+'beam'='MOONBEAM'
Can you help me to learn more?
(Other definitions for moonbeam that I've seen before include "Ray, not the brightest" , "reflective illumination" , "Lunar shaft of light" , "Natural light" , "Night shiner" .)