An achievement to restrict luminescence over the moon (9)
I believe the answer is:
delighted
'over the moon' is the definition.
(I've seen this before)
'an achievement to restrict luminescence' is the wordplay.
'an achievement' becomes 'deed' (deed is a kind of achievement).
'to restrict' is an insertion indicator.
'luminescence' becomes 'light'.
'deed' placed around 'light' is 'DELIGHTED'.
(Other definitions for delighted that I've seen before include "Pleased as Punch" , "Greatly pleased" , "Happy" , "Joyful" , "Over the moon" .)