Scotopic vision is the vision of the eye under low light conditions. The term comes from Greek skotos meaning darkness and -opia meaning a condition of sight.[1] In the human eye cone cells are nonfunctional in low light – scotopic vision is produced exclusively through rod cells which are most sensitive to wavelengths of light around 498 nm (green-blue) and are insensitive to wavelengths longer than about 640 nm (red). Scotopic vision occurs at luminance levels of 10−2 to 10−6 cd/m². In other species, such as the Elephant Hawk-moth (Deilephila elpenor), advanced color discrimination is displayed.[2] Night-vision goggles and similar devices take advantage of the fact that human eyesight is most sensitive to light with a wavelength of 540 nm (slightly lime green).
Mesopic vision occurs in intermediate lighting conditions (luminance level 10−2 to 1 cd/m²) and is effectively a combination of scotopic and photopic vision. This however gives inaccurate visual acuity and color discrimination.
In normal light (luminance level 1 to 106 cd/m²), the vision of cone cells dominates and is photopic vision. There is good visual acuity (VA) and color discrimination.
In scientific literature, one occasionally encounters the term scotopic lux which corresponds to photopic lux, but uses instead the scotopic visibility weighting function.[3]