Artist, one into ballet, shows brilliance (8)
I believe the answer is:
radiance
'brilliance' is the definition.
(I have seen 'Brilliance of glow ' mean 'radiance' so perhaps 'brilliance' could also mean 'radiance')
'artist one into ballet' is the wordplay.
'artist' becomes 'ra' (Royal Academician, member of Royal Academy of Arts).
'one' becomes 'i' (Roman numeral).
'into' means one lot of letters goes inside another.
'ballet' becomes 'dance'.
'i' put within 'dance' is 'diance'.
'ra'+'diance'='RADIANCE'
'shows' is the link.
(Other definitions for radiance that I've seen before include "Brilliance of glow" , "shine" , "Effulgence" , "Great joy" , "Brightness" .)