OK, so xpdev said the room was closed, and one would think that the walls/ceiling are set to cast shadows.  But in P9 and Poser Pro 2012 you could have unseen emitters, props with the visible in camera box un-ticked.  You wouldn't even see them in preview.  Look in the scene hierarchy for any props (or figures) with the "eye" icon greyed out.  Is there an enviro-sphere or skydome in the scene?

 

(xpdev)

*Quote - I begin to think that there is a way of manipulating the materials of objects to get these renderings.
But do such a thing in the room very large and full of objects would be an endless work. *

     Having a lot of light sources is effortless using mesh lights.  There are over two hundred in this scene:

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Poser 12, in feet.  

OSes:  Win7Prox64, Win7Ultx64

Silo Pro 2.5.6 64bit, Vue Infinite 2014.7, Genetica 4.0 Studio, UV Mapper Pro, UV Layout Pro, PhotoImpact X3, GIF Animator 5