Evolution requires an organism to change by a series of infinitesimal mutations, each one leading to the next stable, functioning form. Each predecessor in the succession would still perform the function, although in a more crude fashion. If a cell is irreducibly complex, however, then any predecessor would not be able to perform the required function and the organism could not survive. This discussion is included here because of Behe's interesting treatment of vision, a topic of foundational importance to the lighting professional. His analysis is summarized in the following.
All quotes are from pp.
15-25 of Darwin's Black Box. The human visual system represents an astounding degree of complexity to anyone familiar with its operation. Even in Darwin's day it was known that the eye acted in a manner similar to a camera, with the iris dilating and constricting to allow more or less light in depending on the ambient light level present. The cornea acts to refract light onto the lens which in turn focuses the image on the retina. A variety of specialized cells in the retina detect both achromatic contrast as well as variations in color.