Seaside location, sunny and happening (8)
I believe the answer is:
Here is my best explanation:
'seaside location' is the definition.
(I've seen this before)
'sunny and happening' is the wordplay.
'sunny' becomes 'bright' ('bright' can be similar in meaning to 'sunny').
'and' says to put letters next to each other.
'happening' becomes 'on'.
(Other definitions for brighton that I've seen before include "City", "South-coast resort", "Where the Prince Regent built his Pavilion", "Graham Greene wrote ` `........ Rock' '", "Sussex seaside resort", "Sussex city (with Hove)", "South coast city combined with Hove", "This resort", "seaside location" and "Resort on the south coast of England".)