Light refractor (5)
I believe the answer is:
prism
'light refractor' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for prism that I've seen before include "Cut-glass object" , "Female character in The Importance of Being Ernest -- optical device" , "Triangular piece of glass, optical device" , "source of colourful viewing?" , "Refracting glass" .)