Really simple and cool model. Nice design by @DesignMakeTeach.
I added a small hole on the bottom where a switch can be placed. There are also some supports for the switch inside the object. Something like one of the switches here:
Adafruit Industries Breadboard-friendly SPDT Slide Switch
The inside measurement of the holder for the switch is 11.5mm X 5.85mm
There is a battery holder and cover that snaps in to keep wires tight so you don't need to solder anything to the battery. A CR2032 battery was used.
I very poorly soldered the wire ends to the switch and the LED, just good enough to work. Glued together afterwards.
Enjoy the lighted tetrahedron.