Chibitronics ( https://chibitronics.com ) makes Circuit Stickers, which include LEDs and some effects and logic components. Those make it a lot easier to do paper electronics. Before they existed, one had to solder surface mount LEDs to copper tape.
I will try to get a making-of video edited together soon. In the meantime, you can see them in some of my other projects, including my light-up icosahedra:
… and last year’s light-up pop up card (starting at 4:41 in the video):
