There was [earlier work](http://www.applied-math.org/optical_tempest.pdf) on pulling Ethernet data from the LEDs of a 100MBps switch, as they were hard-wired to the cable.

There was also a paper from around the same time about a keyboard hack that flashes the caps lock key imperceptibly fast but brightly enough so that a remote watcher can see the encoded keystrokes on your curtains or ceiling, but I can't seem to find that one.