In the 1990s, James Turrell continued to expand his artistic exploration of light and space, solidifying his reputation as a master of creating immersive experiences that challenge the viewer's perception. During this decade, Turrell's works ranged from site-specific installations to ambitious projects that engaged with natural landscapes on a grand scale. One notable project from the 1990s is "Atlan" (1995), installed at Art Tower Mito in Ibaraki, Japan. This work employed ultraviolet and tungsten light, showcasing Turrell's signature approach to blending artificial light with the architectural environment to alter the viewer's spatial perception​ (Art21)​. Another significant installation in Japan, "Afrum-Proto" (1996), featured quartz halogen corner projection, further exploring the interaction between light and architecture to create visual illusions​ (Art21)​. In the United States, Turrell created "Hi Test," a site-specific permanent installation at the Mondrian Hotel in West Hollywood, California, in 1997. This piece once again exemplified his ability to transform spaces through the strategic use of mixed media​ (Art21)​. Additionally, "The Light Inside," a site-specific permanent installation at The Museum of Fine Arts in Houston, Texas, completed in 1999, utilized electric lights, wires, metal, and paint to craft an environment that engages directly with the viewer's sensory experience​ (Art21)​. Turrell's work in the 1990s was not limited to installations within buildings. His ongoing, ambitious project, Roden Crater, situated outside Flagstaff, Arizona, exemplifies his deep engagement with the natural environment and celestial phenomena. Although the project had been underway since 1979, the 1990s saw continued development of this extinct cinder cone volcano into a massive naked-eye observatory designed for experiencing celestial events. The project's scale and complexity highlight Turrell's commitment to altering human perception of space and light, integrating art with the surrounding landscape in a profound way​ (Wikipedia)​. Throughout the decade, Turrell also continued to develop his "Skyspaces" series—enclosed rooms with an opening in the roof designed to frame and enhance the viewer's experience of the sky. These works, spread across various locations worldwide, emphasize the dynamic relationship between light, space, and viewer perception. Turrell's Skyspaces invite contemplation and a deepened awareness of the natural light and the cosmos, making them quintessential to understanding his artistic vision​ (Wikipedia)​. James Turrell's work in the 1990s encapsulates his ongoing investigation into the perceptual and emotional effects of light and space. Through a combination of site-specific installations and larger, landscape-integrated projects like Roden Crater, Turrell challenged traditional boundaries of art and perception, inviting viewers into immersive experiences that transcend ordinary visual engagement. His works from this period are critical to understanding the trajectory of contemporary art's engagement with light and space, marking a significant chapter in Turrell's distinguished career.