From Stoneback Audio:
A new kind of musical instrument that replaces the wood and sound used by acoustic musical instruments with electrical currents and light waves. The physics behind sound and light are similar, so the light guitar has musical qualities similar to those found in acoustic instruments. However, light is more complex than sound and this complexity leads to new instrument behaviors.
Since light waves produced by a light musical instrument aren't audible, the waves are measured and recorded. This audio unit exactly recreates the "sound" of the instrument using those measurements. It does this in a way that allows you to change properties of the light guitar to suit your particular music and still be physically accurate. A nearly infinite number of guitar tones are at your fingertips. Plug any instrument into your Mac and hear the light!