She opens up when the lights are low (4)

I believe the answer is:

iris

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'she' is the definition.
(I've seen this before)

I don't understand how the rest of the clue works.

(Other definitions for iris that I've seen before include "Flag - part of eye" , "Flower and eye membrane" , "bit of mince pie" , "Rainbow - flag" , "Lily" .)

I've seen this clue in the Evening Standard.

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