Seal broke right beam (5)
I believe the answer is:
laser
'beam' is the definition.
(laser beam is a kind of beam)
'seal broke right' is the wordplay.
'broke' indicates anagramming the letters.
'right' becomes 'r' (common abbreviation).
'seal' with letters rearranged gives 'lase'.
'lase'+'r'='LASER'
(Other definitions for laser that I've seen before include "Device producing an intense beam of light or radiation" , "Intense light generator" , "modern light industry" , "Intense and concentrated beam of light" , "Device for concentrating light" .)