Creat a spotlight with fog terned on for it. Put it outside the room, aim it at the wall through the window. Render from inside the room. You will have to mess around with the settings of things to get it just right. But this gets you started down the right path I belive. Oh and since you said sunset.. put a little bit of orign color on the spotlight. you might have to light up the rest of the room with lower intencity lights.