The profoundly positive effect that light has on both the immune system and a person's emotional stability is examined in this informative reference that pays particular attention to naturally lit interior spaces. Although architects and physicians in the ancient world recognized that the light levels necessary to promote well-being were much higher than those required for vision, the knowledge seems to have been lost from regular practice. Bringing together historical evidence, traditional wisdom, and the latest scientific findings, this comprehensive reference explains how to use light-especially sunlight-to promote health in architecture and enclosed environments.