The Bat signal is an obvious choice for a night light, but how to make one? GE makes a night light which projects an image on the ceiling:
The easiest thing to do seemed to be to start with one of those and replace their image with one of my own. Opening the light was a little tricky. It's secured by three screws which need a special triangular head. Fortunately, they can also be opened with a very small torx head. Once the screws are off, the case opens and you can remove the sphere that contains the light and pop it open.
There's a light, image, and lens assembly inside. Taking it apart, you find a tiny bit of film in the middle which contains the image. I took that out and put it aside to use as a template for size.
Making the Bat symbol was the trickiest part of the operation because it has to be so very, very tiny, ideally no larger than half the diameter of the film circle. I can't work on that scale, but I got close. I made the symbol by folding a slip of paper in half with a similarly sized bit of foil in it. Starting from the fold, I sketched out half of a Bat symbol and cut it out, then removed and unfolded the bit of foil. It ended up being a bit rough, but perfectly symmetrical. This is actually a different and slightly larger version than the one I ended up with, but it demonstrates what I did.
Next, I got some stiff, clear plastic (a bit of packaging that was about to be discarded) and, using the original film as a template, cut out two circles. The Bat symbol went between the clear disks to protect it and keep it in place. The sandwich went into the lens assembly where the old film was, then I reassembled the whole thing. How does it work? Well...