Log improved with shine (4)
I believe the answer is:
glow
'shine' is the definition.
('glow' can be a synonym of 'shine')
'log improved with' is the wordplay.
'improved' indicates an anagram.
'with' becomes 'w' (abbreviation).
'log' anagrammed gives 'glo'.
'glo'+'w'='GLOW'
(Other definitions for glow that I've seen before include "Gentle, warm light" , "Shine, maybe in dark" , "Give out steady light" , "Shine steadily and brightly" , "Shine with warmth, emotion" .)