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Coherence and Interference of Light
Published in Lazo M. Manojlović, Fiber-Optic-Based Sensing Systems, 2022
the star will twinkle and in opposite will not. The coherence length of the light emitted by the star depends on the star temperature (black body radiation) and the atmosphere absorption. Therefore, the coherence length has not the fixed value but depends on the particular star characteristics. However, regardless the star light spectrum, our eyes are sensitive only in a certain wavelength range. According to the spectral luminous efficiency function for photopic vision, an average human eye has a spectral bandwidth ranging from λL ≈ 380 nm to λH ≈ 770 nm, thus having a spectral width of ΔA ≈ λH – λL ≈ 390 nm, and the peak sensitivity at 〈λ〉 ≈ 555 nm. Therefore, the effective coherence length, given by eq 4.74, is equal to lC ≈ 0.8 μm. As the observer looks at the sky during the night, the pupil has the maximal openings of approximately d ≈ 8 mm. So, according to eq 4.79, if the apparent size is smaller then 200 μrad or 40″, the star will twinkle and in opposite will not or its twinkling will be weaker. If we compare this approximate limit value for the star apparent size and the apparent sizes of the particular celestial bodies, shown in Table 4.1, one can see why stars twinkle distinctively from the planets which in some cases may also twinkle but not so noticeable.
Fundamentals of Human Vision and Vision Modeling
Published in H.R. Wu, K.R. Rao, Digital Video Image Quality and Perceptual Coding, 2017
Ethan D. Montag, Mark D. Fairchild
The shape of the luminous efficiency function is often considered as the spectral sensitivity of photopic vision and as such it is a function of the sensitivity of the separate cone types. However, unlike the spectral sensitivities of the cones, the luminosity function changes shape depending on the state of adaptation, especially chromatic adaptation [SS99]. Therefore the luminosity function only defines luminance for the conditions under which it was measured. As measured by HFP and MDB, the luminosity function can be modeled as a weighted sum of L- and M-cone spectral sensitivities with L-cones dominating. The S-cones contribution to luminosity is considered negligible under normal conditions. (The luminosity function of dichromats, those color-deficient observers who lack either the L- or M-cone photopigment, is the spectral sensitivity of the remaining longer wavelength sensitive receptor pigment. Protanopes, who lack the L-cone pigment, generally see “red” objects as being dark. Deuteranopes, who lack the M-cone pigment, see brightness similarly to color normal observers.)
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:
Quantification of Trichromatic Light Sources to Achieve Tunable Photopic and Mesopic Luminous Efficacy of Radiation
Published in LEUKOS, 2019
Qi Yao, Lintao Zhang, Qi Dai, Jim Uttley
There are three vision states for human beings, which are determined by luminance levels (Stockman and Sharpe 2006): scotopic vision (<0.005 cd/m2), mesopic vision (>0.005 cd/m2, <5 cd/m2), and photopic vision (>5 cd/m2; CIE 2010). The spectral sensitivity curves V(λ) and V'(λ) that peak at 555 and 507 nm for photopic vision (Guild 1932) and scotopic vision (Crawford 1949), respectively, are the two standard functions established by CIE to describe sensitivities of these two vision states (Hsia and Graham 1952; Sagawa and Takeichi 1986; Stockman and Sharpe 2000). The spectral sensitivity curve Vmes(λ) in mesopic vision is a linear combination of V(λ) and V'(λ) (Stockman and Sharpe 2006) and varies at different mesopic luminance states. Luminous efficacy of radiation (LER), in lumens per watt, is an important parameter to measure the efficiency of light sources in different vision states. In this work, to differentiate LER in photopic, scotopic, and mesopic vision, we denote them as photopic luminous efficacy of radiation (PLER), scotopic luminous efficacy of radiation (SLER), and mesopic luminous efficacy of radiation (MLER), respectively. Due to the complexity of Vmes(λ), the scotopic/photopic (S/P) ratio (CIE 2010), which is defined as the ratio of LER in scotopic and photopic vision, is proposed to evaluate light source performance in mesopic vision.
Visual Improvements after Perceptual Learning Transfer from Normoxia to Hypoxia
Published in The International Journal of Aerospace Psychology, 2021
Di Wu, Pengbo Xu, Na Liu, Chenxi Li, He Huang, Wei Xiao
Most studies have confirmed hypoxic deterioration in the visual sense (Connolly, 2010, 2011; Connolly & Barbur, 2009), though some studies have obtained varying results (Benedek et al., 2002; Yap et al., 1995). However, it is generally acknowledged that visual functions decrease with increasing altitude. Thus, the protection of the visual function in the hypoxic environment is an important issue in aviation medicine. Consistent with the above note, the current study found that hypoxia was associated with decreased AULCSF, VA and CS at the trained spatial frequency before perceptual learning. Although all visual performances were obviously damaged in hypoxia, the degree of damage was different. In particular, the differences in the AULCSF and CS were larger between normoxia and hypoxia; however, the difference in VA was relatively smaller. One possible reason is that the vision damage in hypoxia is influenced by luminance. In the current study, the VA was measured by a high-contrast Tumbling E Chart made by a high-brightness light box (approximately 1400 cd/m2). Kobrick and Appleton (1971) suggested that the rod cells of the retina play a prominent role in vision in a mesopic environment and that the function of rods is influenced by oxygen saturation before reaching an altitude of 10,000 ft. Correspondingly, Hecht et al. (1946) indicated that photopic vision was dominated by the cone cells of the retina, and the function of cone cells was not influenced by decreasing oxygen saturation below the altitude of 12,800 ft. Connolly and Barbur (2009, 2010, 2011) also suggested that CS would decline significantly when exposed to a hypoxic environment, and this decline in CS would be even more significant in a mesopic environment. Hence, as the altitude increases, vision is damaged earlier in a dark environment than in a brighter environment. Because the VA measurement was performed in a bright environment, the extent of VA damage was milder than that of AULCSF and CS damage in the hypoxic condition.