I just noticed, looking at the work-sheet, that this was a ten minute exposure on Ektachrome T. It is weak daylight cominig in two windows - but the background is painted that way to project the light further across behind the subject shadow side.
Taking about Inv.Sq.Law; the left side is flagged over to dodge excessive exposure.
However, no artificial window can match the real thing for what you might call 'throw'.
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