Figure it produces light separation (5)
I believe the answer is:
prism
I believe this clue is a double definition.
'figure' is the first definition.
(I have seen 'solid figure' mean 'prism' so perhaps 'figure' could also mean 'prism')
'it produces light separation' is the second definition.
(Other definitions for prism that I've seen before include "Light-splitting device" , "Triangular piece of glass to deviate a beam" , "Light-diffracting glass" , "Transparent 3-sided object that separates light into colours" , "Solid figure - light separator" .)