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The Biological Bases of Photoreception in the Process of Image Vision
Published in Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe, Visual and Non-Visual Effects of Light, 2020
Agnieszka Wolska, Dariusz Sawicki, Małgorzata Tafil-Klawe
In low light levels (luminance <0.001 cd/m2), below the cone threshold, vision is scotopic: visual response relies entirely on rod signals (luminance is a photometric measure of the luminous intensity per unit area of light traveling in a given direction). Scotopic vision is characterized by poor visual acuity and lack of color discrimination. In high light levels (luminance ≥3 cd/m2), above rod saturation, vision is photopic: visual response relies entirely on cones. Photopic vision is characterized by good visual acuity and color discrimination. In the intermediate light levels (luminance between 0.001 and 3 cd/m2) between cone threshold and rod saturation, both rods and cones contribute to visual response. This kind of vision, when both rods and cones provide signals to the retinal ganglion cells, is defined as mesopic vision.
Lighting Quality, Comfort, & Control
Published in Samuel Mills, Fundamentals of ARCHITECTURAL LIGHTING, 2018
The human eye can see a range of light intensity of about a million to one. The eye adjusts to different lighting conditions and varies its mode of vision as the lighting levels change. We have all experienced the difference between daytime and night vision. The photoreceptors of light in the eye (rods and cones), have similar sensitivity to light while rods produce a larger response and operate in three different modes: photopic, mesopic, and scotopic vision. Photopic vision occurs at high light levels with high visual acuity, low light sensitivity, and color perception. Scotopic vision occurs in very low light levels with resulting low visual acuity, high light sensitivity, and no color vision. Mesopic vision is a mixed mode with performance based on whether objects lie in the central or peripheral visual zone and shifts toward scotopic vision as light levels decline toward the low threshold of human vision. The contrast ratio of the eye is around 100:1.
Lighting and Communications: Devices and Systems
Published in Zabih Ghassemlooy, Luis Nero Alves, Stanislav Zvánovec, Mohammad-Ali Khalighi, Visible Light Communications, 2017
Luis Nero Alves, Luis Rodrigues, José Luis Cura
Scotopic vision takes place under low light conditions, when only the rod cells inside the retina are active. Their spectral sensitivity is similar in form to the V(λ) curve, for photopic vision. In 1951, the CIE adopted the standard scotopic luminosity function, also available in either tabulated or graphical forms. Scotopic vision sensitivity is expressed by the V′(λ) curve; Figure 2.4 depicts both the curves for comparison. It is readily apparent that the major difference is the peak wavelengths. There is also mesopic vision, which relates to intermediate lighting situations. Under these conditions, both the rod and cone cells inside the retina are active. The sensitivity exhibits intermediate values between V(λ) and V′(λ). Mesopic vision is important for traffic lighting systems, where the road surface luminance stays above the scotopic limit and falls below the photopic limit. Current trends in outdoor lighting are considering mesopic vision for light optimization, due to the fact that photopic vision is a poor predictor of how well humans see at night. The mesopic sensitivity curve is commonly expressed as a linear combination of V(λ) and V′(λ), which is given as:
Calculation of Mesopic Luminance Using per Pixel S/P Ratios Measured with Digital Imaging
Published in LEUKOS, 2019
Mikko Maksimainen, Matti Kurkela, Pramod Bhusal, Hannu Hyyppä
The human retina consists of cone cells used for accurate day and color vision and rod cells applied for dark vision. Day vision is also called “photopic vision,” and dark vision is called “scotopic vision.” The sensitivity peaks for photopic and scotopic visions are 555 nm and 507 nm, respectively (CIE 1990; Crawford 1949). Thus, scotopic vision is more sensitive to shorter wavelength (bluish) light, and photopic vision is more sensitive to longer wavelength (reddish) light. However, in the luminance range of 0.005–5.0 cd/m2, partly scotopic and partly photopic vision applies (CIE 2010). This region is known as the “mesopic region,” and the vision for this region is mesopic vision. In the CIE 191 system for mesopic photometry, the mesopic sensitivity curve is calculated as follows: