I thought I would chime in... I have lit my windows from the inside the last couple of years. I cut white peg board the size of my window frames. I then spent many hours with hot glue securing incandescent mini bulbs into the pre-drilled holes. That was great for the older lights - I have 15 windows...
With the smart string lights, it was simply too expensive to use smart string lights for 15 windows. I seriously considered it, but I just couldn't justify the cost. (The nodes do fit in the peg board if you drill out the holes to 1/2".)
I dcided i would turn my windows into low-resolution matrixes. I'm using 1 rectangular node per window frame. My windows now range from 5 to 15 nodes per window. What I did this year was pull out my old mini lights and add a 4" spacer to the perimeter of the peg board. The spacer is a plastic gutter guard type device sold at lowes. (they come in 3' sections.) I zip tied the gutter guard things around the peg board which gave me a little space between the peg board and the glass. Lastly, I will add a white shower curtain as a screen for a diffuser.
Not perfect, but I generally like the results - and much cheaper than spart strings around the perimeter - and seems to put out light from the whole window instead od just the perimeter.