"A light and sound machine is a  brainwave entrainment tool. The method by which this entrainment occurs is known as the Frequency Following Response (FFR). Through the use of audio (headphones) & visual (eye frames with LEDs) stimulation, listeners are gently guided into specific brainwave states. Each audio beat and pulse is a specific frequency. Our minds "think" in terms of frequency. Brainwaves change frequencies based on neural activity within the brain, be it by hearing, touch, smell, vision and/or taste. These senses respond to activity from the environment and transmits that information to the brain via electrical signals. Hearing + vision are considered the favorable senses for affecting brainwaves safely. By presenting these beats & pulses to the brain, within a few minutes, the brain begins to mimic or follow the same frequencies as the stimuli (the beats and pulses). This process is referred to as entrainment. In essence, these instruments speak to the mind in it's own language - the language of frequency". - Michael Landgraf, Publusher of the AVSJournal mindmachine blog