Along with his colleagues Professor Russell Foster broke the conventional wisdom and discovered a light-sensitive cell inside the eye that had nothing to do with vision. Although much of the scientific community was originally skeptical, these photosensitive Retinal Ganglion Cells (pRGCs) have not only become an accepted part of our biology they have major consequences for people young and old living in every part of the world. That's because pRGCs regulate sleep. In spite of playing no role in vision, these crucial components of the eye use the light exposure in our daily lives to manage an activity so important we spend a third of our lives doing it. In this episode of the show, Professor Foster offers insight into what sleep is, why it matters so very much and what his research means for individuals, businesses and societies as a whole.Russell Foster is the author of three particularly excellent books for a general audience Sleep: A Very Short Introduction, Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing and Seasons of Life: The Biological Rhythms that Enable Living Things to Thrive and Survive.