Fish providing light (3)
I believe the answer is:
ray
This clue is a double definition.
'fish' is the first definition.
(I know that ray is a type of fish)
'light' is the second definition.
(I know that ray is a light)
'providing' is the link.
(Other definitions for ray that I've seen before include "Lindwall" , "Gleam" , "may be electric" , "beamer?" , "Broad flat fish; beam" .)