Radiant silver luminance over town centre (5)
I believe the answer is:
aglow
'radiant' is the definition.
(I've seen this before)
'silver luminance over town centre' is the wordplay.
'silver' becomes 'ag' ('Ag' can be a synonym of 'silver').
'luminance' becomes 'l' (physics abbreviation).
'over' is a charade indicator (letters next to each other).
'town centre' becomes 'ow' (central letters of the word 'town').
'ag'+'l'+'ow'='AGLOW'
(Other definitions for aglow that I've seen before include "Gleaming" , "Lit up" , "Softly bright or radiant" , "Giving out a steady light" , "Shining" .)