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BackgroundMesopic conditions elicit both rod and cone responses, and they are more commonly encountered in daily life than are scotopic conditions; yet visual function outcome measures of mesopic visual acuity (VA) or contrast sensitivity (CS) are rarely evaluated.ObjectiveIn retinitis pigmentosa (RP), we explored whether visual reductions in mesopic versus photopic conditions were correlated with cone or rod function, as well as the between-visit test-retest variability in mesopic measures.MethodsAt each of two visits, 22 RP subjects completed mesopic and photopic ETDRS VA and Pelli-Robson chart CS tests obtained with and without a U23 NoIR 4% transmission filter; testing of perifoveal scotopic cone or rod sensitivity with the AdaptDx; and the Rabin Cone Contrast Test (CCT).ResultsA greater CS reduction in mesopic versus photopic conditions was significantly related to absence of scotopic rod function (p = 0.038) or longer self-reported duration of night vision loss (p = 0.044). VA reductions >0.2 logMAR in mesopic versus photopic conditions were significantly related to reduced cone-mediated scotopic sensitivity (p = 0.038). Significant predictors of the CCT ratio of S-cone to M- and L-cone sensitivity were mesopic VA (p = 0.038) and absence of AdaptDx rod function (p = 0.008). Test-retest 95% coefficients of repeatability were not significantly different when comparing between photopic and mesopic tests of VA (0.16 and 0.12 logMAR, respectively) or CS (0.21 and 0.24 logCS, respectively).ConclusionsPerifoveal scotopic rod and cone function measured with the AdaptDx was significantly correlated with mesopic CS and VA, respectively, which had good, acceptable test-retest repeatability; thus, they appear to be suitable outcome measures to monitor mesopic visual function in clinical practice or trials. RP subjects with reduced mesopic VA and no perifoveal rod function had a greater loss of sensitivity for S-cones than for L-/M-cones.

Linking the activity of neurons, circuits and synapses to human behavior is a fundamental goal of neuroscience. Meeting this goal is challenging, in part because behavior, particularly perception, often masks the complexity of the underlying neural circuits, and in part because of the significant behavioral differences between primates and animals like mice and flies in which genetic manipulations are relatively common. Here we relate circuit-level processing of rod and cone signals in the non-human primate retina to a known break in the normal seamlessness of human vision – a surprising inability to see high contrast flickering lights under specific conditions. We use electrophysiological recordings and perceptual experiments to identify key mechanisms that shape the retinal integration of rod- and cone-generated retinal signals. We then incorporate these mechanistic insights into a predicti\ve model that accurately captures the cancellation of rod- and cone-mediated responses and can explain the perceptual insensitivity to flicker.

Contrast sensitivity (CS), the ability to detect small spatial changes of luminance, is a fundamental aspect of vision. However, while visual acuity is commonly measured in eye clinics, CS is often not assessed. At issue is that tests of CS are not highly standardized in the field and that, in many cases, optotypes used are not sensitive enough to measure graduations of performance and visual abilities within the normal range. Here, in order to develop more sensitive measures of CS, we examined how CS is affected by different combinations of glare and ambient lighting in young healthy participants. We found that low levels of glare have a relatively small impact on vision under both photopic and mesopic conditions, while higher levels had significantly greater consequences on CS under mesopic conditions. Importantly, we found that the amount of glare induced by a standard built-in system (69 lux) was insufficient to induce CS reduction, but increasing to 125 lux with a custom system did cause a significant reduction and shift of CS in healthy individuals. This research provides important data that can help guide the use of CS measures that yield more sensitivity to characterize visual processing abilities in a variety of populations with ecological validity for non-ideal viewing conditions such as night time driving.

Purpose: To establish age‐related, normal limits of monocular and binocular spatial vision under photopic and mesopic conditions. Methods: Photopic and mesopic visual acuity (VA) and contrast thresholds (CTs) were measured with both positive and negative contrast optotypes under binocular and monocular viewing conditions using the Acuity‐Plus (AP) test. The experiments were carried out on participants (age range from 10 to 86 years), who met pre‐established, normal sight criteria. Mean and ± 2.5σ limits were calculated within each 5‐year subgroup. A biologically meaningful model was then fitted to predict mean values and upper and lower threshold limits for VA and CT as a function of age. The best‐fit model parameters describe normal aging of spatial vision for each of the 16 experimental conditions investigated. Results: Out of the 382 participants recruited for this study, 285 participants passed the selection criteria for normal aging. Log transforms were applied to ensure approximate normal distributions. Outliers were also removed for each of the 16 stimulus conditions investigated based on the ±2.5σ limit criterion. VA, CTs and the overall variability were found to be age‐invariant up to ~50 years in the photopic condition. A lower, age‐invariant limit of ~30 years was more appropriate for the mesopic range with a gradual, but accelerating increase in both mean thresholds and intersubject variability above this age. Binocular thresholds were smaller and much less variable when compared to the thresholds measured in either eye. Results with negative contrast optotypes were significantly better than the corresponding results measured with positive contrast (p < 0.004). Conclusions: This project has established the expected age limits of spatial vision for monocular and binocular viewing under photopic and high mesopic lighting with both positive and negative contrast optotypes using a single test, which can be implemented either in the clinic or in an occupational setting. [ABSTRACT FROM AUTHOR]

Due to the typical ambient light levels in inhabited places and light pollution of the night sky, most naked-eye astronomical observations are performed nowadays under mesopic conditions. The luminance (cd/m2) associated with the brightness of the night sky specified in the astronomical logarithmic scale of magnitudes per square arcsecond (mag/arcsec2) is strongly dependent on the spectrum of the sky, because the spectral sensitivity of the human visual system is not coincident with the standard photometric bands used in astronomy. The conversion between these two families of photometric systems was previously analyzed for observers presumed to be either fully photopically or scotopically adapted. In this work, we deduce the transformation equations between the astronomical and visual photometric systems for specifying and reporting the sky brightness in the mesopic range, within the framework of the MES-2 system for visual performance-based mesopic photometry. It is shown that the dependence of the conversion factors on the correlated color temperature of the night sky reaches a minimum spread for adaptation luminances of 0.5–1.0 cd/m2. The sky luminances corresponding to 22.0 mag/arcsec2 in the Johnson-Cousins V band (the assumed brightness of a natural night sky devoid of light pollution) span, for 1.0 cd/m2 adaptation, a relatively small range of ~195–215 μcd/m2 in the absolute (AB) magnitude system and ~210–225 μcd/m2 in the Vega-referenced one. [ABSTRACT FROM AUTHOR]

It is often desirable or unavoidable to display Virtual Reality (VR) or stereoscopic content at low brightness. For example, a dimmer display reduces the flicker artefacts that are introduced by low-persistence VR headsets. It also saves power, prolongs battery life, and reduces the cost of a display or projection system. Additionally, stereo movies are usually displayed at relatively low luminance due to polarization filters or other optical elements necessary to separate two views. However, the binocular depth cues become less reliable at low luminance. In this paper, we propose a model of stereo constancy that predicts the precision of binocular depth cues for a given contrast and luminance. We use the model to design a novel contrast enhancement algorithm that compensates for the deteriorated depth perception to deliver good-quality stereoscopic images even for displays of very low brightness. [ABSTRACT FROM AUTHOR]

To investigate the visual function correlates of self-reported vision-related night driving difficulties among drivers. One hundred and seven drivers (age: 46.06 ± 8.24, visual acuity [VA] of 0.2logMAR or better) were included in the study. A standard vision and night driving questionnaire (VND-Q) was administered. VA and contrast sensitivity were measured under photopic and mesopic conditions. Mesopic VA was remeasured after introducing a peripheral glare source into the participants' field of view to enable computation of disability glare index. Regression analyses were used to assess the associations between VND-Q scores, and visual function measures. The mean VND-Q score was -3.96±1.95 logit (interval scale score: 2.46±1.28). Simple linear regression models for photopic contrast sensitivity, mesopic VA, mesopic contrast sensitivity, and disability index significantly predicted VND-Q score (P <0.05), with mesopic VA and disability glare index accounting for the greatest variation (21 %) in VND-Q scores followed by photopic contrast sensitivity (19 %), and mesopic contrast sensitivity (15 %). A multiple regression model to determine the association between the predictors (photopic contrast sensitivity, mesopic VA, mesopic contrast sensitivity, and disability index) and VND-Q score yielded significant results, F (4, 102) = 8.58, P < 0.001, adj. R2 = 0.2224. Seeing dark-colored cars was the most challenging vision task. Changes in mesopic visual acuity, photopic and mesopic contrast sensitivity, as well as disability glare index are associated with and explain night driving-related visual difficulties. It is recommended to incorporate measurement of these visual functions into assessments related to driving performance. [ABSTRACT FROM AUTHOR]

The effect of uniform lighting on face identity processing is little understood, despite its potential influence on our ability to recognize faces. Here, we investigated how changes in uniform lighting level affected face identification performance during face memory tests. Observers were tasked with learning a series of faces, followed by a memory test where observers judged whether the faces presented were studied before or novel. Face stimuli were presented under uniform bright or dim illuminations, and lighting across the face learning and the memory test sessions could be the same ("congruent") or different ("incongruent"). This led to four experimental conditions: (1) Bright/Dim (learning bright faces, testing on dim faces); (2) Bright/Bright; (3) Dim/Bright; and (4) Dim/Dim. Our results revealed that incongruent lighting levels across sessions (Bright/Dim and Dim/Bright) significantly reduced sensitivity (d') to faces and introduced conservative biases compared to congruent lighting levels (Bright/Bright and Dim/Dim). No significant differences in performance were detected between the congruent lighting conditions (Bright/Bright vs. Dim/Dim) and between the incongruent lighting conditions (Bright/Dim vs. Dim/Bright). Thus, incongruent lighting deteriorated performance in face identification. These findings implied that the level of uniform lighting should be considered in an illumination-specific face representation and potential applications such as eyewitness testimony. [ABSTRACT FROM AUTHOR]

A study by Gao et al found that the Newton method may not converge for certain combinations of the photopic luminance and the ratio of scotopic and photopic luminance for computing the adaptation coefficient m, for the CIE MES2 system for mesopic photometry. Hence, they proposed to use the Bisection‐Newton method. In this short note, we propose the Newton method with a new initial guess for computing m. Numerical simulation has shown the proposed method not only converges, but also converges faster than the Bisection‐Newton method. [ABSTRACT FROM AUTHOR]

The effect of uniform lighting on face identity processing is little understood, despite its potential influence on our ability to recognize faces. Here, we investigated how changes in uniform lighting level affected face identification performance during face memory tests. Observers were tasked with learning a series of faces, followed by a memory test where observers judged whether the faces presented were studied before or novel. Face stimuli were presented under uniform bright or dim illuminations, and lighting across the face learning and the memory test sessions could be the same (“congruent”) or different (“incongruent”). This led to four experimental conditions: (1) Bright/Dim (learning bright faces, testing on dim faces); (2) Bright/Bright; (3) Dim/Bright; and (4) Dim/Dim. Our results revealed that incongruent lighting levels across sessions (Bright/Dim and Dim/Bright) significantly reduced sensitivity (d’) to faces and introduced conservative biases compared to congruent lighting levels (Bright/Bright and Dim/Dim). No significant differences in performance were detected between the congruent lighting conditions (Bright/Bright vs. Dim/Dim) and between the incongruent lighting conditions (Bright/Dim vs. Dim/Bright). Thus, incongruent lighting deteriorated performance in face identification. These findings implied that the level of uniform lighting should be considered in an illumination-specific face representation and potential applications such as eyewitness testimony.

When a display of red spots or hearts on a blue surround is moved around under dim light, the spots appear to wobble or flutter relative to the surround (the "fluttering hearts" effect). We explain this as follows: Rods and cones both respond to the hearts. Rods are more sluggish than cones, with a latency of ∼50 ms, and they are also much more sensitive to blue than to red (the Purkinje shift; Purkinje, 1825). Thus a red spot oscillating on a blue ground produces a double image: a light spot seen by the cones, followed by a trailing dark spot seen by the rods. These interacting spots of opposite luminance polarity move like "reverse phi" (Anstis, 1970) and this generates the fluttering hearts effect. We find that hearts flutter most markedly at or near mesopic equiluminance, when the red is lighter than the blue as seen by the cones, but darker than the blue as seen by the rods. These same red/blue luminance ratios give rise to two new illusions: the ghostly twin illusion, and the reversal of red/blue grating movement.

PurposeTo evaluate visual function variations in eyes with age-related macular degeneration (AMD) compared to normal eyes under different light/contrast conditions using a time-dependent visual acuity testing instrument, the Central Vision Analyzer (CVA).MethodsOverall, 37 AMD eyes and 35 normal eyes were consecutively tested with the CVA after assessing best-corrected visual acuity (BCVA) using ETDRS charts. The CVA established visual thresholds for three mesopic environments (M1 (high contrast), M2 (medium contrast), and M3 (low contrast)) and three backlight-glare environments (G1 (high contrast, equivalent to ETDRS), G2 (medium contrast), and G3 (low contrast)) under timed conditions. Vision drop across environments was calculated, and repeatability of visual scores was determined.ResultsBCVA significantly reduced with decreasing contrast in all eyes. M1 scores for BCVA were greater than M2 and M3 (P

Purpose: To explore the differential effects of age and eccentricity on the perception of motion at photopic and mesopic light levels. Methods: Thirty‐six visually normal participants (18 younger; mean age 25 years, range: 20–31) and (18 older; mean age 70 years, range: 60–79) underwent two testing sessions, one at photopic and one at mesopic light levels. In each session, motion perception was tested binocularly at two eccentricities (centrally, and peripherally at 15° rightwards and 5° superior to the horizontal) for four motion tasks: minimum contrast of a drifting Gabor to identify motion direction (motion contrast); translational global motion coherence; biological motion embedded in noise and the minimum duration of a high‐contrast Gabor to determine the direction of motion, using two Gabor sizes to measure spatial surround suppression of motion. Results: There was a significant main effect of light condition (higher thresholds in mesopic) for motion contrast (p < 0.001), translational global motion (p = 0.001) and biological motion (p < 0.001); a significant main effect of age (higher thresholds in older adults) for motion contrast (p < 0.001) and biological motion (p = 0.04) and a significant main effect of eccentricity (higher thresholds peripherally) for motion contrast (p < 0.001) and biological motion (p < 0.001). Additionally, we found a significant three‐way interaction between light levels, age and eccentricity for translational global motion (similar increase in mesopic thresholds centrally for both groups, but a much larger deterioration in older adult's peripheral mesopic thresholds, p = 0.02). Finally, we found a two‐way interaction between light condition and eccentricity for translational global motion (higher values in central mesopic relative to peripheral photopic, p = 0.001) and for biological motion (higher values in peripheral mesopic relative to central photopic, p < 0.001). Conclusions: For the majority of tasks assessed, motion perception was reduced in mesopic relative to photopic conditions, to a similar extent in both age groups. However, because some older adults exhibited elevated thresholds even under photopic conditions, particularly in the periphery, the ability to detect mesopic moving stimuli even at high contrast was markedly impaired in some individuals. Our results imply age‐related differences in the detection of peripheral moving stimuli at night that might impact hazard avoidance and night driving ability. [ABSTRACT FROM AUTHOR]

Purpose: The measurement of standard visual acuity (VA) is the most well‐known part of any ophthalmic examination to indicate visual function. Despite this, it is insensitive in detecting early disease changes. Therefore, other visual function tests have been developed including low luminance VA (LLVA) and low luminance deficit (LLD). This scoping literature review aims to summarise the current published applications of LLVA and LLD assessments to evaluate their utility as clinical markers and research outcome measures in a variety of ophthalmic conditions. Recent findings: Sixty‐five peer‐reviewed publications were included. LLVA was pioneered for use in geographic atrophy, a subtype of age‐related macular degeneration, which remains the mainstay of its clinical application. However, other studies have reported additional useful applications in inherited retinal diseases including rare maculopathies and rod‐cone dystrophies. Although there are some variations in testing methodology, use of the standard Early Treatment Diabetic Retinopathy Study (ETDRS) chart with a 2.0 log unit neutral density filter is the most popular approach. The optimal testing luminance is still to be defined. Summary: Overall, LLVA is an earlier clinical marker of change in central retinal function than standard VA. It has been shown to be a risk factor for disease progression and a better indicator of a patient's level of everyday visual function. It is inexpensive and simple to implement using readily available standard ophthalmic equipment. [ABSTRACT FROM AUTHOR]

Copyright of Spektrum der Augenheilkunde is the property of Springer Nature and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Purpose: The effect of duration of optotype presentation on visual acuity measures has been extensively studied under photopic conditions. However, systematic data on duration dependence of acuity values under mesopic and scotopic conditions is scarce, despite being highly relevant for many visual tasks including night driving, and for clinical diagnostic applications. The present study aims to address this void. Methods: We measured Landolt C acuity under photopic (90 cd/m2), mesopic (0.7 cd/m2), and scotopic (0.009 cd/m2) conditions for several optotype presentation durations ranging from 0.1 to 10 s using the Freiburg Acuity and Contrast Test. Two age groups were tested (young, 18–29 years, and older, 61–74 years). Results: As expected, under all luminance conditions, better acuity values were found for longer presentation durations. Photopic acuity in young participants decreased by about 0.25 log units from 0.1 to 10 s; mesopic vision mimicked the photopic visual behavior. Scotopic acuities depended more strongly on presentation duration (difference > 0.78 log units) than photopic values. There was no consistent pattern of correlation between luminance conditions across participants. We found a qualitative similarity between younger and older participants, despite higher variability among the latter and differences in absolute acuity: Photopic acuity difference (0.1 vs. 10 s) for the older participants was 0.19 log units, and scotopic difference was > 0.62 log units. Conclusion: Scotopic acuity is more susceptible to changes in stimulus duration than photopic vision, with considerable interindividual variability. The latter may reflect differences in aging and sub-clinical pathophysiological processes and might have consequences for visual performance during nocturnal activities such as driving at night. Acuity testing with briefly presented scotopic stimuli might increase the usefulness of acuity assessment for tracking of the health state of the visual system. [ABSTRACT FROM AUTHOR]

Invariant spatial context can guide attention and facilitate visual search, an effect referred to as "contextual cueing." Most previous studies on contextual cueing were conducted under conditions of photopic vision and high search item to background luminance contrast, leaving open the question whether the learning and/or retrieval of context cues depends on luminance contrast and ambient lighting. Given this, we conducted three experiments (each contains two subexperiments) to compare contextual cueing under different combinations of luminance contrast (high/low) and ambient lighting (photopic/mesopic). With high-contrast displays, we found robust contextual cueing in both photopic and mesopic environments, but the acquired contextual cueing could not be transferred when the display contrast changed from high to low in the photopic environment. By contrast, with low-contrast displays, contextual facilitation manifested only in mesopic vision, and the acquired cues remained effective following a switch to high-contrast displays. This pattern suggests that, with low display contrast, contextual cueing benefited from a more global search mode, aided by the activation of the peripheral rod system in mesopic vision, but was impeded by a more local, fovea-centered search mode in photopic vision. [ABSTRACT FROM AUTHOR]

Featured Application: This work clarifies light sources' circadian effect and mesopic vision effect in road lighting for the first time, and guides circadian and efficient outdoor lighting application. Several models on the circadian effect have been applied to indoor circadian lighting design, but applications in road lighting have not yet been clarified. Based on existing models and circadian research, we examined equivalent melanopic lux (EML), circadian light (CLA), and circadian stimulus (CS) representing the circadian effect and the S/P ratio representing the mesopic vision effect, among a dataset of light sources at photopic adaptation illuminance values of 1, 3, 10, 30, and 100 lx. The results show that the S/P ratio correlates with EML and CS (or CLA) much stronger than it correlates with color temperature. The EMLs of light sources are below 50 EML in mesopic vision, and the CSs of most light sources are below or around the threshold value of 0.05. We conclude that the circadian effect is not a significant issue in mesopic vision under most conditions and that optimization for mesopic efficiency is still a good strategy. There are quite a few light sources that may achieve both ideal mesopic efficiency and low CS. This work clarifies the circadian effect and mesopic vision effect performance of light sources in mesopic vision and will help guide choosing suitable light sources and optimization strategies for road lighting. [ABSTRACT FROM AUTHOR]

The study aims to propose an approach of white LED spectral optimization based on mesopic luminance and color gamut volume for dim lighting conditions. Three optimal white LED spectra with relatively higher mesopic luminance and color gamut volume, the highest mesopic luminance, and the largest gamut volume are recommended for reducing energy consumption and enhancing color perception and recognition of human eyes. The theoretical simulation shows that the spectra with higher correlated color temperatures (CCT) and S/P-ratio increase the mesopic luminance and also extend the range of color gamut with the decreasing of lighting level. An evaluation model is developed to faster predict mesopic luminance, color gamut volume, and S/P ratio for lighting applications. [ABSTRACT FROM AUTHOR]

Temporal contrast detected by rod photoreceptors is channeled into multiple retinal rod pathways that ultimately connect to cone photoreceptor pathways via Cx36 gap junctions or via chemical synapses. However, we do not yet understand how the different rod pathways contribute to the perception of temporal contrast (changes in luminance with time) at mesopic light levels, where both rods and cones actively respond to light. Here, we use a forced-choice, operant behavior assay to investigate rod-driven, temporal contrast sensitivity (TCS) in mice of either sex. Transgenic mice with desensitized cones (GNAT2cp-/D line) were used to identify rod contributions to TCS in mesopic lights. We found that at low mesopic lights (400 photons/s/ju,m2 at the retina), control and GNAT2cp/B mice had similar TCS. Surprisingly, at upper mesopic lights (8000 photons/s/jum2), GNATcpft3 mice exhibited a relative reduction in TCS to low (< 12 Hz) while maintaining normal TCS to high (12-36 Hz) temporal frequencies. The rod-driven responses to high temporal frequencies developed gradually over time (>30 min). Furthermore, the TCS of GNAT2cp/u and GNAT2'p/D::Cx36 mice matched closely, indicating that transmission of high-frequency signals (1) does not require the rod-cone Cx36 gap junctions as has been proposed in the past; and (2) a Cx36-independent rod pathway(s) (e.g., direct rod to OFF cone bipolar cell synapses and/or glycinergic synapses from All amacrine cells to OFF ganglion cells) is sufficient for fast, mesopic rod-driven vision. These findings extend our understanding of the link between visual circuits and perception in mouse. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate the impact of correlated color temperature (CCT) of LED light source on human vision performance in mesopic region. First, six CCTs (3500, 4000, 4500, 5000, 5700, and 6500 K) were assessed using mesopic photometry model MES-2. The calculation results indicated that the mesopic luminance had a positive correlation with CCT. Then, reaction time experiment was conducted in an experimental box designed to simulate the mesopic application environments. Ten observers of different ages and gender participated to make response after target appears under different lighting conditions. Experiment results showed that reaction time had a negative correlation with CCT, which is coherent with that the mesopic luminance increased with the increasing of CCT.

Copyright of Przegląd Elektrotechniczny is the property of Przeglad Elektrotechniczny and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Despite the fact that a 2-degree spectral sensitivity curve (SSC) is extensively used in scientific research and relevant applications, the choice between the 10-degree or the 2-degree photopic SSCs in practical applications for the calculation of scotopic/photopic ratios (S/P ratios) depends on actual needs. We examined S/P ratios for more than 300 light sources for correlated colour temperatures (CCTs) from 2000 K to 8000 K and blackbody radiant spectra from 10000 K to 45000 K using 2- and 10-degree SSCs. Results showed that the ratio of the S/P values calculated using the 10-degree and 2-degree SSCs was approximately equal to 0.916. The average mesopic luminance difference increased from 0% to 5.7% at a photopic adaptation luminance from 0.005 to 5 cd/m2. For most practical applications, the mesopic luminance values calculated using these two SSCs were different by several percentage units, yet these differences could be neglected. At extremely high CCTs over 10000 K, the mesopic luminance difference may approximate the maximum value of 16%. This work proposes the conversion coefficients for S/P ratios and the transforming mesopic luminance values calculated for 2- and 10-degree SSC systems. These results may help researchers clarify differences between the S/P ratios calculated using different SSCs. [ABSTRACT FROM AUTHOR]

This study describes a method of measuring the pixelwise S/P ratio using a calibrated digital camera and applying these S/P ratios to calculate mesopic luminance values. An example of using the developed method is presented. Further improvements for the method are discussed. [ABSTRACT FROM AUTHOR]

This study attempts to quantify and optimize the luminous efficacy of radiation (LER) of trichromatic light sources in both photopic and mesopic visions. A new chromaticity-guided rather than spectrum-guided optimization approach is provided. LER contour maps formed by the gamut area of the three light source units are drawn in the chromaticity diagram. Based on these, functional models of LER in photopic and mesopic visions as well as scotopic/photopic (S/P) ratios are established as a function of chromaticity coordinates. Increasing trends for LER and S/P ratios in corresponding contour maps are proposed, which allow quick estimation and synthesis for ideal performance. By using the functional model, the ideal LER, S/P ratio of trichromatic light sources, and their combinations can be achieved. Based on this work, tunable combinations of LER and S/P ratios with chromaticity information can be achieved, which could provide more application possibilities for trichromatic light sources. [ABSTRACT FROM AUTHOR]

Purpose: To investigate the effect of uncorrected astigmatism on night driving performance on a closed‐road circuit. Methods: Participants included 10 drivers (mean age 24.4 ± 7.0 years), with low to moderate bilateral astigmatism (0.75–1.50 DC), who were regular contact lens (CL) wearers. Vision and night driving performance were assessed in a cross‐over design with a toric CL and a best‐sphere spherical CL. Binocular visual function measures included photopic and mesopic visual acuity (VA), contrast sensitivity (CS), mesopic motion sensitivity and glare tests (Mesotest®II and Halometer). Night‐time driving performance was assessed on a closed‐road circuit, which included measures of sign recognition, hazard detection and avoidance, pedestrian recognition distances, lane keeping, speed and overall driving score. Results: Correction of astigmatism with toric CL significantly improved mesopic VA, photopic and mesopic CS, mesopic motion sensitivity, and reduced glare (p < 0.05), compared to the spherical CL; there were no significant effects of visual correction type on photopic VA. Correction of astigmatism using toric CL resulted in significant improvements in night driving performance, compared to driving with spherical CL, particularly for sign recognition, avoidance of low contrast hazards, increased pedestrian recognition distances and overall driving score (p < 0.05). Conclusions: Correction of low to moderate levels of astigmatism had significant positive effects on night‐time driving performance and related tests of visual performance. This has important implications for optical corrections to improve night road safety of drivers with astigmatism. [ABSTRACT FROM AUTHOR]

This paper discusses the importance of adapting conventional photometric quantities when lighting systems with low luminance levels are under analysis, as public lighting or external lighting in general. In this sense, it is presented an alternative methodology for lighting projects in street lighting, considering the mesopic photometry. The CIE recommendation 191:2010 proposes correc-tion factors that convert conventional photometric quantities (photopic) into quantities adapted to the corresponding mesopic level. However, a necessary parameter to obtain these correction factors is the relationship between the scotopic and photopic light fluxes of a light source (S/P ratio), which requires special equip-ment that it is not easily available to engineers, technicians and lighting designers. Thus, this paper proposes a general equation that provides the S/P ratio as a function of the correlative color temperature and the color rendering index of the light source, which are information provided in the manufacturers' catalogs or electric lamp packages. To illustrate the application of the exper-imentally derived relationship, a typical street lighting project is considered, specifically a retrofit from HPS lamps to modern LED luminaires. In this case, the conventional routine must be changed, allowing the adaptation of conventional quantities to mesopic quantities without need for specialized equipment. The case study evidences that the use of mesopic photometry in con-junction with more appropriate technologies, such as LED lumi-naires, lead to a higher energy efficiency of the system. [ABSTRACT FROM AUTHOR]

The mammalian visual system operates over an extended range of ambient light levels by switching between rod and cone photoreceptors. Rod-driven vision is sluggish, highly sensitive, and operates in dim or scotopic lights, whereas cone-driven vision is brisk, less sensitive, and operates in bright or photopic lights. At intermediate or mesopic lights, vision transitions seamlessly from rod-driven to cone-driven, despite the profound differences in rod and cone response dynamics. The neural mechanisms underlying such a smooth handoff are not understood. Using an operant behavior assay, electrophysiological recordings, and mathematical modeling we examined the neural underpinnings of the mesopic visual transition in mice of either sex. We found that rods, but not cones, drive visual sensitivity to temporal light variations over much of the mesopic range. Surprisingly, speeding up rod photoresponse recovery kinetics in transgenic mice improved visual sensitivity to slow temporal variations, in the range where perceptual sensitivity is governed by Weber's law of sensation. In contrast, physiological processes acting downstream from phototransduction limit sensitivity to high frequencies and temporal resolution. We traced the paradoxical control of visual temporal sensitivity to rod photoresponses themselves. A scenario emerges where perceptual sensitivity is limited by: (1) the kinetics of neural processes acting downstream from phototransduction in scotopic lights, (2) rod response kinetics in mesopic lights, and (3) cone response kinetics as light levels rise into the photopic range. [ABSTRACT FROM AUTHOR]

Luminous fiber is a kind of new functional material which is prepared by melt spinning process adding colored pigments and luminous material into polyamide fiber. Based on the experimental data of the emission spectra and the test luminance of the luminous fibers, the effect of emissive colors of luminous fibers on the equivalent luminance in mesopic vision is analyzed. The results show that the effect of emissive colors of white, yellow, blue, and green luminous fibers on equivalent luminance increases firstly with the reduction of retinal illuminance, and then decrease. The effect is maximum when retinal illuminance is.1Td. The emissive color of the red luminous fiber has evident effects on the equivalent luminance, and the factor of emissive color should be considered fully to evaluate the actual visibility. [ABSTRACT FROM AUTHOR]

Three psycho-visual experiments were carried out to investigate visual afterimage characteristics of high luminance LEDs under dark surround conditions. The results show that the luminance of illumination, exposure time and background luminance are the primary factors influencing the afterimage’s duration, the color difference between stimulus and background, and visibility. Besides, visual afterimage characteristics are strongly correlated with the luminance contrast between the stimulus and the background, but not for the color difference with a white background. A third-order polynomial regression model was proposed to accurately estimate the afterimage duration, the color difference between stimulus and background, and visibility. The model performance showed high R-squared, low root-mean-square error (RMSE) and mean absolute error (MAE) values between the predicted and visual characteristics.

Several models on the circadian effect have been applied to indoor circadian lighting design, but applications in road lighting have not yet been clarified. Based on existing models and circadian research, we examined equivalent melanopic lux (EML), circadian light (CLA), and circadian stimulus (CS) representing the circadian effect and the S/P ratio representing the mesopic vision effect, among a dataset of light sources at photopic adaptation illuminance values of 1, 3, 10, 30, and 100 lx. The results show that the S/P ratio correlates with EML and CS (or CLA) much stronger than it correlates with color temperature. The EMLs of light sources are below 50 EML in mesopic vision, and the CSs of most light sources are below or around the threshold value of 0.05. We conclude that the circadian effect is not a significant issue in mesopic vision under most conditions and that optimization for mesopic efficiency is still a good strategy. There are quite a few light sources that may achieve both ideal mesopic efficiency and low CS. This work clarifies the circadian effect and mesopic vision effect performance of light sources in mesopic vision and will help guide choosing suitable light sources and optimization strategies for road lighting.

The study aims to propose an approach of white LED spectral optimization based on mesopic luminance and color gamut volume for dim lighting conditions. Three optimal white LED spectra with relatively higher mesopic luminance and color gamut volume, the highest mesopic luminance, and the largest gamut volume are recommended for reducing energy consumption and enhancing color perception and recognition of human eyes. The theoretical simulation shows that the spectra with higher correlated color temperatures (CCT) and S/P-ratio increase the mesopic luminance and also extend the range of color gamut with the decreasing of lighting level. An evaluation model is developed to faster predict mesopic luminance, color gamut volume, and S/P ratio for lighting applications.

Contrast sensitivity (CS), the ability to detect small spatial changes of luminance, is a fundamental aspect of vision. However, while visual acuity is commonly measured in eye clinics, CS is often not assessed. At issue is that tests of CS are not highly standardized in the field and that, in many cases, optotypes used are not sensitive enough to measure graduations of performance and visual abilities within the normal range. Here, in order to develop more sensitive measures of CS, we examined how CS is affected by different combinations of glare and ambient lighting in young healthy participants. We found that low levels of glare have a relatively small impact on vision under both photopic and mesopic conditions, while higher levels had significantly greater consequences on CS under mesopic conditions. Importantly, we found that the amount of glare induced by a standard built-in system (69 lux) was insufficient to induce CS reduction, but increasing to 125 lux with a custom system did cause a significant reduction and shift of CS in healthy individuals. This research provides important data that can help guide the use of CS measures that yield more sensitivity to characterize visual processing abilities in a variety of populations with ecological validity for non-ideal viewing conditions such as night time driving.

Apart from the well-known loss of color vision and of foveal acuity that characterizes human rod-mediated vision, it has also been thought that night vision is very slow (taking up to 40 min) to adapt to changes in light levels. Even cone-mediated, daylight, vision has been thought to take 2 min to recover from light adaptation. Here, we show that most, though not all adaptation is rapid, taking less than 0.6 s. Thus, monochrome (black-white-gray) images can be presented at mesopic light levels and be visible within a few 10th of a second, even if the overall light level, or level of glare (as with passing headlamps while driving), changes abruptly.

Numerous independent field research studies, trying to establish actual energy savings when replacing high-pressure sodium (HPS) luminaires with LED ones in street lighting, had serious deficiencies. Therefore, our approach was based on equal photopic or mesopic luminance levels when comparing street lighting installations. In addition, a novel approach, considering energy efficiency indicators of LED luminaires in both the standard and reduced lighting regimes, enabled the determination of their energy saving potential in various dimming scenarios. The stated requirements for a case street could represent guidelines for future pilot projects in this field. The comparison of the measurement results obtained using both the telemanagement system and electricity meters, which was done for the first time, showed that the former can enable reliable assessment of electrical parameters. It was concluded that when using quality LED instead of quality HPS luminaires energy savings could be between 31% and 60% when applying multi-stage dimming scenarios. An important finding is that the LED luminaire power factor can considerably decrease when reducing the luminous flux. Another important finding is that the increase of the street luminance level to its initial value in early morning hours only slightly increases the overall electricity consumption. [ABSTRACT FROM AUTHOR]