James Turrell studied optics and perceptual psychology in college, but he gravitated towards art as his curiosity led him to investigate light itself. His thinking and work are compelling to scientists, artists, and laypeople because his understanding of light comes from a personal process of investigation, resulting in works of astounding beauty. In this Webcast of a lecture, sponsored by the Sonoma County Museum, Turrell discusses his experiences manipulating pure light and how it became his artistic medium. He reveals how this early work led him to discover Roden Crater in Arizona and to create his subsequent lifelong project of transforming the crater into an astronomical observatory.