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In vision science of visual perception, scotopic vision (or scotopia) is the vision of the eye under low-light conditions. (2025). 9780198821489, Oxford University Press. ISBN 9780198821489 The term comes from the Ancient Greek skotos, meaning 'darkness', and -opia, meaning 'a condition of sight'. In the human eye, are nonfunctional in low visible spectrum. Scotopic vision is produced exclusively through , which are most sensitive to of around 498 nm (blue-green) and are insensitive to wavelengths longer than about 640 nm. (2025). 9780262514279, MIT Press. ISBN 9780262514279 Under scotopic conditions, light incident on the retina is not encoded in terms of the spectral power distribution. Higher visual perception occurs under scotopic vision as it does under photopic vision.
Mesopic vision occurs in intermediate lighting conditions (luminance level 10−3 to 100.5 candela/m2) and is effectively a combination of scotopic and photopic vision. This gives inaccurate visual acuity and color discrimination.
In normal light (luminance level 10 to 108 candela/m2), the vision of cone cells dominates and is photopic vision. There is good visual acuity (VA) and color discrimination.
The behavior of the rhodopsin photopigment explains why the human eye cannot resolve lights with different spectral power distributions under low light. The reaction of this single photopigment will give the same quanta for 400 nm light and 700 nm light. Therefore, this photopigment only maps the rate of absorption and does not encode information about the relative spectral composition of the light.
In scientific literature, one occasionally encounters the term scotopic lux which corresponds to photopic lux, but uses instead the scotopic visibility weighting function. Photobiology: The Science of Light and Life (2002), Lars Olof Björn, p.43 , The scotopic luminosity function is a standard function established by the Commission Internationale de l'Éclairage (CIE) and standardized in collaboration with the ISO.
The maximum scotopic efficacy is 1700 lm/W at 507 nm (compared with 683 lm/W at 555 nm for maximum photopic efficacy). While the ratio between scotopic and photopic efficacies is only around 2.5 counted at peak sensitivity the ratio increases strongly below 500 nm.
Another reason that vision is poor under scotopic vision is that rods, which are the only cells active under scotopic vision, converge to a smaller number of neurons in the retina. This many-to-one ratio leads to poor spatial frequency sensitivity.
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