Humans have been using light and sound to achieve altered states of consciousness for thousands of years. Primitive cultures used flickering fires and rythmic drumming to induce these altered states. Today, you can choose from a wide variety of electronic brain-wave machines which use light and/or sound to alter brain-wave activity. Brain-wave activity ranges from fully awake to deep dreamless sleep.

I first saw one of these at a hackers convention in Holland. I subsequently made one of my own and used it as my part in an exhibition with the help mainly of stuff gleamed from the archives of Hack Canada