Pat Arneson’s VidiSynth is a DIY video controlled synthesizer.
The light sensors create interesting and complex sounds, based on the intensity of different areas of the screen. If the sensors are attached to an LCD screen you get relatively normal square wave tones but if you use a CRT screen (TV or monitor) you get ‘extra noisy and buzzy goodness’ because of way the screen refreshes.
In the video, Paul Sobczak demonstrates his expanded version of the VidiSynth.
Details on the VidiSynth project are available here.