If the window(s) subtend only a small angle, then the external light has to be extremely bright. My first problem with Poser in this regard is that it leaks light at corners - anywhere two surfaces meet at right angles.

Second, the space occupied by the windows relative to everything that is not self-lit means you have to use a really high number of samples. This will make it exceedingly slow.

Third you will have to have a lot of bounces - also slow.

I have been struggling with this indoor-lit-by-sky-via-window scenario for several weeks, as I'm trying to pre-light the new room for Bedroom/Furniture Set One. I can't do it.

My suggestion would be to fake it and not fully enclose the room. Open the wall where the windows are and put the camera there facing in. I haven't tried that yet, as I've been perfecting materials and the indoor/night lights first.

In the render above, which is night (black outside the windows) I have three point lights. IDL is still a very important factor in this appearance, as without it the room lighting looks more harsh.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)