Ray of light down the shaft (7)
I believe the answer is:
sunbeam
'ray of light' is the definition.
(sunbeam is a kind of ray of light)
'down the shaft' is the wordplay.
'down' becomes 'sun' (I can't explain this - if you can you should give a lot more credence to this answer).
'the shaft' becomes 'beam' (synonyms).
'sun'+'beam'='SUNBEAM'
Can you help me to learn more?
(Other definitions for sunbeam that I've seen before include "Bright ray -- bus name (anag)" , "Ray of natural light" , "Bright shaft of daylight" , "sheds a bit of light" , "Ray of solar light" .)