The walls of the recesses are painted white, but by reflecting the light from the fluorescent lamps appear to be different colours.
The overall effect of the two pieces is to engender an optical illusion in which the three-dimensional space of the installation appears to collapse into two dimensions - the apertures seem to alternate between their actual "void" form and being on a single plane with the surrounding walls, ceiling and floor.
[1][2] Much of Turrell's work is dedicated to the exploration of the aesthetic properties and "thingness" of light, drawing inspiration from sources as wide-ranging as the works of the perceptual phenomenologist Merleau Ponty (with whom Turrell became familiar through his background in psychology) to those of artists such as Claude Monet and Mark Rothko.
[5] In 1990, the works were reinstalled at the Museum of Contemporary Art in San Diego, purchased with funds from the Elizabeth W. Russell Foundation.
[6] Each installation of the pieces required significant preparatory work by Turrell, who used a combination of diagrams and scale models, as well as extensive on-site experimentation, to determine the correct proportions and layout for the chambers.