Here's an O scale church I scratchbuilt for a customer in Massachusetts. I wanted the WOW factor and the only thing besides church bells ringing I could think of were illuminated stained glass windows.
After a Google search I found the windows on-line in connection with the building plans for a protestant church yet to be built in the mid-west. I copied the file, resized it and then printed several copies on clear acetate. These were cut to fit and glued inside each window opening.
Next, I built a lighting grid so an LED would illuminate each window. I added a voltage regulator so I could power the lights with 16VAC.
The photos shows the illuminated windows as they would look at about dusk.