Swirling fog later with fading light (9)
I believe the answer is:
afterglow
'fading light' is the definition.
(I've seen this before)
'swirling fog later with' is the wordplay.
'swirling' is an anagram indicator.
'with' becomes 'w' (short for with).
'fog'+'later'='foglater'
'foglater' anagrammed gives 'afterglo'.
'afterglo'+'w'='AFTERGLOW'
(Other definitions for afterglow that I've seen before include "trace of sunset" , "Light, lingering" , "The satisfaction" , "appearing when sun has set?" , "Light once the actual source has gone" .)