Every LED is a Communications Port
Although almost every electronic device made today contains a microcontroller
and (theoretically) has sufficient capability to communicate with similar devices,
the cost of including a communication link often precludes two devices that
are sitting side-by-side from talking to each other. This is the “last centimeter
problem”.
With LEDComm technology, every LED becomes a potential communication
path. This has broad implications because LEDs are widely used as power-on
http://www.merl.com/publications/docs/TR2003-35.pdfhttps://en.wikipedia.org/wiki/LED_circuit#LED_as_light_sensor