Almost all texts on the eye, photometry, or lighting discuss these differences, some in great detail. The effects are generally well known, but they are not often taken into account in considerations of nighttime lighting. There is now, however, a growing interest in such issues. This information sheet discusses some of the aspects. It is only a very brief introduction to the issues of vision at low light levels.
Scotopic vision is rod vision.
The rods have no color vision, so there is no color perception at such very low lighting levels, no matter what the color of the light source or of the object being viewed. As the illumination level increases, we enter the mesopic range, where both rods and cones are in use, so vision is both peripheral and central, and color begins to become apparent. At much higher levels, the eye cannot tolerate the intensity, and one shades ones eyes, turns away, or otherwise avoids the very high intensity. The edges of the retina, where rods dominate, are particularly sensitive to motion. At the lowest lighting levels, one sees motion but little or no detail.