Went fast over stream of light, then dispersed (7)
I believe the answer is:
sprayed
'dispersed' is the definition.
(spraying is a kind of dispersing)
'went fast over stream of light' is the wordplay.
'went fast' becomes 'sped' (I've seen this in another clue).
'over' indicates putting letters inside.
'stream of light' becomes 'ray' (a ray of light).
'sped' placed around 'ray' is 'SPRAYED'.
'then' is the link.
(Other definitions for sprayed that I've seen before include "showered" , "Sprinkled" , "Sent out liquid in very small drops" .)