Fair illumination (5)
I believe the answer is:
light
This clue is a double definition.
'fair' is the first definition.
(as in fair hair)
'illumination' is the second definition.
(I know that illumination can be written as light)
(Other definitions for light that I've seen before include "solution to clue" , "skedaddle!" , "Not dark; not heavy" , "Illumination weighs very little" , "Eminent person" .)