"A holocron, short for holographic chronicle, was an organic crystal-lattice device which stored phenomenal quantities of data guarded by the device's gatekeeper. Holocrons were used to hold information on force techniques and instruction manuals by force users beginning with the Sith and then the Jedi some three thousand years later." - Wookieepedia
A small prop Jedi Holocron I made for a friend, takes about 10-15 hours to print. The side panels are designed to be glued 3 to each inner half, so that they lock together. Inside is a 1"x1" space for a small FX lighting, this can be as simple as a few blue LEDs around a CR2032 battery; as shown in the photos.
I printed the inner two halves in transparent PETG filament at 225C, the outer side panels were printed in white ABS at 235C.