Not to brag or anything, but I make some mean window rays (check out my Backhall feature in the Showcase forum)!
The best window rays are comprised of multiple billboards (fixed axis, pointing in the direction of your spotlight) rotated so that the player can see them when not directly in front of the window, and also see them "glowing" outwards while oriented directly in front of the window. (I can upload screenies if this is confusing)
Change the color of each billboard to 0.05 to 0.1 for each R, G, and B value. This will fade it so it isn't so blindingly bright, causing the rays to be EXTREMELY bright when they overlap), and so that you wont see the billboard "cut in" to your window. To help avoid this, move the billboards so that they begin at the floor (or as far away as you want them to go), and end just before the window. If you don't understand what I mean, I can post some screenshots of good and bad billboard compounds.
I also add a billboard that is oriented parallel to the window, so the window has a sort of glow to it. This also helps avoid billboards "cutting in" to the window.
In the screenies I also noticed your spotlights gobo map is upside down. Just rotate your spotlight so it is oriented correctly