|Most framed art, including Animation Cels, are visible due to light reflecting off the art's surface. That's not the case with transparencies. To be seen they must be illuminated from behind. In the past our only option was to build a light box. They worked but were bulky, hot, and required an electrical cord and outlet.
Today, "behind the art" illumination is possible with LED strips and panels. This Snoopy and Jan-Vive collectable 4x5 transparency is back-lit over a battery powered LED panel. The back of the frame, below, is open, allowing access to the battery pack and the on/off switch.