Mitxela.com uses some very tiny 0201 LEDs to make LED matrix earrings. Off-the-shelf LED studs are used with the plastic gemstone replaced with an intricate circuit board sandwich with the LEDs.
To get the scale of the tiny LEDs, here is one on an 8 pin DIP chip:
The LEDs were surface mounted on one tiny circuit board and a second board with the microcontroller was attached to the back, sandwich style.
Mounting the PCB sandwich in the studs makes a very cute piece of jewelry:
See the video below (YouTube), read more about the project here and see the code on GitHub.