Unmasking in dark room? (8)
I believe the answer is:
exposure
'unmasking' is the definition.
(I've seen this before)
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for exposure that I've seen before include "Appearance before the public" , "being unmasked" , "Vulnerability; photograph" , "Laying open to public view" , "Act of laying open or bare" .)