I found a solution for my opaque windows with your objects and PVR 1.5. [=D>] [=D>] [=D>]
In this first picture, light panels (in front of window) are at 0% : we see external flowers.
In this second picture, we have opacity and light with :
at left of the door, the light panel is at 5%,
at right of the door: a light panel is at 50%.
=> We don't see external objects, just light.
[:)]