I did some testing, and here's the result:

• The room is closed and no windows
• No light
• I added an object primitive (square hig-res) and set the value to ambient_color 126:126:126 and ambient_value to 3

if the size of the square-hig res are almost like the room I get this result quite acceptable

Poser Pro 2014 SR 1 on Windows 7 64 bit
I use IDL, Gamma Correction and EZSkin for all final renders.