If this photo was taken circa 1870 (Prue's earlier posting) , I believe they were still experimenting with artificial lighting - magnesium flares and powder, etc. It's more likely that it would be a very long exposure with natural lighting, as you say, Denn.
I'm yet to be convinced that it isn't a 'set' of some kind but, bearing in mind the story of the two women, could it possibly be some kind of spiritualist/supernaturalist room for communing with whatever they communed with ('the other side'). It might explain the strange collection of objects and arrangements.
Somehow, it does give the feeling of Jane Eyre's mad woman in the attic or Rosemary's Baby.
Gadget