some background for using LED's for bi-directional communication:
LED's as sensors
Looks like there may be some use for this kind of thing in the FX community as a replacement(or alternative) for LDR's.
Bill Bowden has a circuit here:
that can output a control voltage based on the light sensing capabilities of the LED. Looks like you could easily interface it to an envelope follower or LFO driving a LED.
imagine being able to control something like the resonant peaks of a filter in 3D using a matrix of such sensors like here:
watch the video link, it's way cool!
how practical would this approach be?