James Turrell has innovated photographic techniques that allow light to have a physical presence. Using holography to make the light itself the subject rather than the medium, Turrell creates colored light installations that appear to possess mass and take up space as planes, cubes, pyramids, and tunnels. Turrell’s series “Skyspace,” (begun in the 1970s), which he has constructed around the world, are enclosed spaces open to the sky through an aperture in the roof that enable viewers to observe changes in light from minute to minute and season to season, what has been described as a religious experience.