She lets in the light (4)
I believe the answer is:
iris
'she' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for iris that I've seen before include "- - Murdoch, novelist" , "Flowers in the eye?" , "may open up in camera" , "Pupil's place?" , "Flag - flower - girl" .)