In
the study
The Study is an English-language private education all-girls school in Westmount, Quebec. The school was founded in 1915 by a young Englishwoman named Margaret Gascoigne. The Study offers a bilingual mother tongue education to 386 students from K ...
of
visual perception
Visual perception is the ability to detect light and use it to form an image of the surrounding Biophysical environment, environment. Photodetection without image formation is classified as ''light sensing''. In most vertebrates, visual percept ...
, scotopic vision (or scotopia) is the vision of the
eye
An eye is a sensory organ that allows an organism to perceive visual information. It detects light and converts it into electro-chemical impulses in neurons (neurones). It is part of an organism's visual system.
In higher organisms, the ey ...
under low-
light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
conditions. The term comes from the
Greek
Greek may refer to:
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group
*Greek language, a branch of the Indo-European language family
**Proto-Greek language, the assumed last common ancestor of all kno ...
''skotos'', meaning 'darkness', and ''-opia'', meaning 'a condition of sight'. In the
human eye
The human eye is a sensory organ in the visual system that reacts to light, visible light allowing eyesight. Other functions include maintaining the circadian rhythm, and Balance (ability), keeping balance.
The eye can be considered as a living ...
,
cone cell
Cone cells or cones are photoreceptor cells in the retina of the vertebrate eye. Cones are active in daylight conditions and enable photopic vision, as opposed to rod cells, which are active in dim light and enable scotopic vision. Most v ...
s are nonfunctional in low
visible light
Light, visible light, or visible radiation is electromagnetic radiation that can be perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400–700 nanometres (nm ...
. Scotopic vision is produced exclusively through
rod cell
Rod cells are photoreceptor cells in the retina of the eye that can function in lower light better than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in ...
s, which are most
sensitive to
wavelength
In physics and mathematics, wavelength or spatial period of a wave or periodic function is the distance over which the wave's shape repeats.
In other words, it is the distance between consecutive corresponding points of the same ''phase (waves ...
s of around 498 nm (blue-green)
and are insensitive to wavelengths longer than about 640 nm. Under scotopic conditions, light incident on the retina is not encoded in terms of the
spectral power distribution
In radiometry, photometry (optics), photometry, and color science, a spectral power distribution (SPD) measurement describes the Power (physics), power per unit area per unit wavelength of an illumination (lighting), illumination (radiant exitan ...
. Higher visual perception occurs under scotopic vision as it does under photopic vision.
Retinal circuitry
Of the two types of
photoreceptor cell
A photoreceptor cell is a specialized type of neuroepithelial cell found in the retina that is capable of visual phototransduction. The great biological importance of photoreceptors is that they convert light (visible electromagnetic radiation ...
s in the
retina
The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...
,
rods dominate scotopic vision. This dominance is due to the increased sensitivity of the
photopigment
Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore Moiety (chemistry), moiety of photosensitive chromoproteins, such as the pigments involved in ph ...
molecule expressed in rods, as opposed to those in
cones. Rods signal light increments to
rod bipolar cells which, unlike most types of
bipolar cells, do not form direct connections with
retinal ganglion cells – the output neurons of the retina. Instead, two types of
amacrine cell –
AII and A17 – allow lateral information flow from rod bipolar cells to cone bipolar cells, which in turn contact ganglion cells. Thus, rod signals, mediated by amacrine cells, dominate scotopic vision.
Occurrence
Scotopic vision occurs at
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...
levels of 10
−3 to 10
−6 cd/m
2. Other species are not universally color blind in low-light conditions. The elephant hawk-moth (''
Deilephila elpenor'') displays advanced color discrimination even in dim starlight.
Mesopic vision
Mesopic vision, sometimes also called twilight vision, is a combination of photopic and scotopic vision under low-light (but not necessarily dark) conditions. Mesopic levels range approximately from 0.01 to 3.0 cd/m2 in luminance. Most ni ...
occurs in intermediate lighting conditions (
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...
level 10
−3 to 10
0.5 cd/m
2) and is effectively a combination of scotopic and
photopic vision
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher vis ...
. This gives inaccurate
visual acuity
Visual acuity (VA) commonly refers to the clarity of visual perception, vision, but technically rates an animal's ability to recognize small details with precision. Visual acuity depends on optical and neural factors. Optical factors of the eye ...
and color discrimination.
In normal light (
luminance
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls wit ...
level 10 to 10
8 cd/m
2), the vision of cone cells dominates and is
photopic vision
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher vis ...
. There is good visual acuity (VA) and color discrimination.
Wavelength sensitivity

The normal human observer's relative wavelength sensitivity will not change due to background illumination under scotopic vision. The wavelength sensitivity is determined by the
rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the ''RHO'' gene and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim ...
photopigment
Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore Moiety (chemistry), moiety of photosensitive chromoproteins, such as the pigments involved in ph ...
. This is a red pigment seen at the back of the eye in animals that have a white background to their eye called
Tapetum lucidum
The ; ; : tapeta lucida) is a layer of tissue in the eye of many vertebrates and some other animals. Lying immediately behind the retina, it is a retroreflector. It Reflection (physics), reflects visible light back through the retina, increas ...
. The pigment is not noticeable under
photopic
Photopic vision is the vision of the eye under well-lit conditions (luminance levels from 10 to 108 cd/m2). In humans and many other animals, photopic vision allows color perception, mediated by cone cells, and a significantly higher vis ...
and
mesopic conditions. The principle that the wavelength sensitivity does not change during scotopic vision led to the ability to detect two functional cone classes in individuals. If two cone classes are present, then their relative sensitivity will change the behavioral wavelength sensitivity. Therefore, experimentation can determine "the presence of two cone classes by measuring wavelength sensitivity on two different backgrounds and noting a change in the observer's relative wavelength sensitivity."
The behavior of the
rhodopsin
Rhodopsin, also known as visual purple, is a protein encoded by the ''RHO'' gene and a G-protein-coupled receptor (GPCR). It is a light-sensitive receptor protein that triggers visual phototransduction in rod cells. Rhodopsin mediates dim ...
photopigment
Photopigments are unstable pigments that undergo a chemical change when they absorb light. The term is generally applied to the non-protein chromophore Moiety (chemistry), moiety of photosensitive chromoproteins, such as the pigments involved in ph ...
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. 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 International Organization for Standardization (ISO ; ; ) is an independent, non-governmental, international standard development organization composed of representatives from the national standards organizations of member countries.
Me ...
.
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.
Resolution
For adaption to occur at very low levels, the human eye needs to have a large sample of light across the signal in order to get a reliable image. This leads to the human eye being unable to resolve high
spatial frequencies in low light since the observer is spatially averaging the light signal.
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
In mathematics, physics, and engineering, spatial frequency is a characteristic of any structure that is periodic across position in space. The spatial frequency is a measure of how often sinusoidal components (as determined by the Fourier tra ...
sensitivity.
General perception
High-level visual perception is similar with scotopic as with photopic sight with people
reading
Reading is the process of taking in the sense or meaning of symbols, often specifically those of a written language, by means of Visual perception, sight or Somatosensory system, touch.
For educators and researchers, reading is a multifacete ...
with unimpaired accurately (though twice as long
fixations), able to
recognize faces, and show a
face inversion effect.
See also
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References
Further reading
*
* (Review)
{{DEFAULTSORT:Scotopic Vision
Eye
Vision