Okay bear with me mike

Do you want a random set of images shown or do you want some form of control over all images presented.

From your example you wish to display a certain group of images either on or off in a specific section then tile that specific group around your whole scene is this correct.

If this is the case and using your example of

Light_on Light_off Light_off
Light_off Light_off Light_on

What I would do is create a larger texture with the group of windows looking exactly how you want them on or off then I would just UV tile them this would also render faster in that you wouldn't need the expression or the blender node instead it's just one large texture with the specific window colors set to whats required.

Is this what you require if it is and it works I would like to see the end result. Sound Interesting.