This chapter explores the fundamental aspects of illumination, covering natural and artificial light sources and their applications in interior spaces. It introduces the significance of lighting in shaping ambiance and functionality, discussing light generation and essential units of measure for a comprehensive understanding. The chapter emphasizes the importance of day lighting in architectural design, showcasing how natural light creates sustainable and visually appealing spaces. It delves into smart systems for managing daylight in buildings. Moving on to artificial light, the chapter traces the evolution of lighting technologies, analyzing various types like incandescent, fluorescent, LED, etc., and their applications.Practical applications of artificial lighting in diverse interior spaces are examined, enhancing functionality and aesthetics. The chapter explores lighting strategies for bedrooms, offices, retail stores, and specialized environments. Additionally, it delves into futuristic trends, including smart lighting, human-centric concepts, and advanced materials like OLEDs and quantum dots, shaping the future of lighting design.