The Purple Room creates a pure color environment: an enclosed space within which people can study their response to night vision, twilight vision, and vision under unusual illuminants, such as the purple light of lavender fields. The perception of shapes and depth change as light levels are gradually brought down to the threshold between activation of the rod and the cone cells in the retina.
The experience starts in complete darkness. People entering the Purple Room would initially be unable to see their hands in front of their faces. After a brief period of complete darkness, their eyes will adjust to see. The first level of illumination is night vision, where no colors can be seen. The illumination is then raised further to enter the realm of twilight vision, where some muted colors are seen. Finally vivid blues and purples are introduced. The participants may be surprised to see the silhouettes of others appearing blurry. Perhaps more striking is that motion perception is altered by the purple light. Rapidly moving objects appear to move slowly and slowly moving objects do not appear to move at all. This can cause paradoxical situations, where an observer does not see something move, yet they notice that its position changes from time to time.