Twinkling beam (5)
I believe the answer is:
flash
I believe this is a double definition.
'twinkling' is the first definition.
('flash' can be a synonym of 'twinkling')
'beam' is the second definition.
(thesaurus)
(Other definitions for flash that I've seen before include "Short gleam of light" , "Streak" , "emblem on uniform" , "Momentary brightness" , "Conspicuously display" .)