Good base, light (4)
I believe the answer is:
glow
'light' is the definition.
(glow is a kind of light)
'good base' is the wordplay.
'good' becomes 'g' (abbreviation).
'base' becomes 'low' ('low' can be a synonym of 'base').
'g'+'low'='GLOW'
(Other definitions for glow that I've seen before include "Brightness" , "Emit light and heat without flame" , "Emanate light" , "Burn without flame" , "rosy colour" .)