Brilliant dismount (6)
I believe the answer is:
alight
I believe this is a double definition.
'brilliant' is the first definition.
(brilliant can mean shining or lit up)
'dismount' is the second definition.
(alight can mean to get off or dismount)
(Other definitions for alight that I've seen before include "Leave a vehicle - burning" , "Touch down" , "Ignited; get off" , "Come to rest, settle" , "Descend, being on fire" .)