Artist Robert Mathy created "Light Sensitive Fingertips" -- a musical instrument that has light sensitive phototransistors in the tips of the fingers. It's played by moving the sensors over light sources of varying intensity:

Light, emitted by the displays of activated mobile phones, functions as the origin of the sounds. As each mobile phone's display generates a different light frequency, each results in an audio signal with a different pitch. In addition, other electronic devices, such as flashing bicycle lights, can be used to generate rhythmic tones.

In the links, you can find a video of Mathy playing this instrument.

Link via GearFuse | Video | Photo: Robert Mathy