Crankies do not have to be backlit, but it increases the drama factor if you are able to perform in a darkened room.
The amount of light you need depends on the thickness
of the scroll. A thin, translucent parchment paper needs less light than two thicknesses of felt. If the light is too strong for the scroll, you will get a "hot spot" in the middle of the screen. Not enough light, and images will be hard to see.
You might need to experiment with different bulbs.