Infinity mirror
A mirror tunnel is a set of mirrors, one fully reflective mirror and one "one-way mirror", set up so that the one-way or partially reflective mirror reflects an image back onto the fully reflective mirror, in a recursive manner, creating a series of smaller and smaller reflections that recede into an infinite distance. This effect is also seen when a subject stands between two fully reflective mirrors, as in a changing room or house of mirrors.
In a classic mirror tunnel, a set of light bulbs, LEDS, or other point source lights are placed at the periphery of a fully reflective mirror, and a second, partially reflective "one-way" mirror, is placed immediately above it. When a subject looks into the surface of the partially reflective mirror, the lights appear to recede into infinity, creating the appearance of a tunnel of lights of great depth.
Explanation of effect
The reason why the reflections recede into the distance is that the light actually is travelling the distance it appears to be travelling. In a two-inch thick mirror tunnel, with the light source itself one inch from the front two-way mirror, light from the source only travels that one inch. The first reflection travels one inch to the rear mirror and then 2 inches to, and through the front mirror, a total of 3 inches. The second reflection travels two inches from front mirror to back mirror, and again two inches from the back mirror to, and through the front mirror, totaling 4 inches, plus the first reflection (3 inches) making the second reflection 7 inches away from the front mirror. Each successive reflection adds 4 more inches to the total; 3rd reflection = 11 inches, 4th = 15 inches, and so on.
The multiply-reflected light follows a folded path which is much deeper than the arrangement of mirrors.
Use in artworks
The mirror tunnel effect has been used by artists such as Chul Hyun Ahn, Josiah McElheny, Hans Kotter, Yayoi Kusama, Iván Navarro, and Dmitri Obergfell.