To me this looks like mostly ambient window light with a lot of white walls for soft fill all around. They don't seem to be filling in much with other light sources, so the shots are actually fairly underexposed and there's not much pop to them. It does look very natural (if boring) and adds to a verité feeling that suits some stories. Not for nothin' you can shoot very fast and cheap this way because you aren't spending tons of time setting up lights. Another reason you see it in a lot of indie films.
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