A shining example, but not for long (5)
I believe the answer is:
flash
'long' is the definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?
'a shining example but not for' is the wordplay.
'a shining' becomes 'fl' (I can't explain this - if you can you should give a lot more credence to this answer).
'example' becomes 'as' (I've seen this in other clues).
'but' becomes 'tho' (I've seen this in other clues).
'not' suggests deleting specific letters.
'for' becomes 'to' (eg both can mean 'in the opinion of').
'tho' with 'to' removed is 'h'.
'fl'+'as'+'h'='FLASH'
Can you help me to learn more?
(Other definitions for flash that I've seen before include "Moment" , "Mo" , "Streak" , "Scintillate" , "sort of flooding" .)