A pencil, perhaps, is a little light (3)
I believe the answer is:
ray
I believe this is a double definition.
'a pencil' is the first definition.
(I have seen 'Pencil of light ' mean 'ray' so perhaps 'pencil' could also mean 'ray')
'is a little light' is the second definition.
(I've seen this before)
'perhaps' is the link.
(Other definitions for ray that I've seen before include "Shaft, beam" , "Pencil of light" , "A little light" , "beamer?" , "Broad flat fish; beam" .)