Definition of brightens:
(v) :
(transitive, figuratively) To make more cheerful and pleasant; to enliven
(v) :
(transitive) To make bright or brighter in color.
(v) :
(transitive) To make illustrious, or more distinguished; to add luster or splendor to
(v) :
(intransitive) To grow bright, or more bright in color; to clear up
(v) :
(intransitive) To become brighter or more cheerful in mood