This work is a 8 x 15 array of full-color LEDs, driven by an embedded Linux board. Each LED is addressable, and optical sensors trigger interactions when someone is in proximity. The algorithm is a digital simulation of the 2-dimensional wave equation. Think of water in the bathtub: it's quiescent when not disturbed. However triggering an optical sensor does the digital equivalent of throwing a rock in a pool: it disturbs the initial conditions, and sends ripples propagating away.