You need:
A plastic container with either a flat and smooth bottom or top
A length of rope lights (I used a 12 foot lenght)
Black plastic friendly spray paint
Hot glue gun and lots of hot glue sticks
Blue painter's tape
Piece of vellum paper to fit window (optional)
This container is great because it's not very deep and is really sturdy. I got it at Target. As you can see, the lid is not smooth and flat...
but the bottom is. This actually is better because it makes the light box more stable. The lid/top is wider than the bottom.
Tape off the inside bottom of the box. And spray paint the inside of the box and the inside of the lid.
Drill a hole in the box for the cord to go through. Hot glue the rope lights to the lid. I used a lot of glue.
Optional. tape a piece of vellum paper to the inside of the window.
Put the pieces together and you're ready to go!
What can you do with a light box?
Play with translucent toys such as blocks, sheer fabrics, hair gel ziplocks, pieces of paper, water beads etc etc