The design of light is a fundamental aspect shaping our spatial experiences. This lecture delves into the intricate relationship between human vision and the qualities of natural light, encompassing its spectrum, dynamics, and temporal variations. By examining the interplay of direct sunlight, diffuse overcast light, and the interplay of highlights and shadows, we uncover how it relates to spatial perception, Highlighting the pivotal role of light, colour, and contrast, we elucidate how their strategic deployment molds the visual quality and ambiance of a space, and how these qualities could be interpreted with electrical light. Through a synthesis of scientific insights and design practices, this lecture offers a holistic perspective and illuminates the bridge between theoretical understanding and practical application.