Low Illumination Levels Research Articles

Self-Supplying Photovoltaic-Hygroelectric Coupling System Powering Internet of Things Sensors.

The rapid advancement in the Internet of Things (IoT) has prompted a proliferation of sensor applications with increasing focus on harnessing environmental energy sources for powering these sensors. However, owing to the variability inherent in climatic and geographic conditions, a singular approach to environmental energy harvesting often fails to deliver sustainable and reliable power. Hygroelectric technology, leveraging the electrical coupling between nanostructured materials and water to convert moisture-derived energy into electricity, complements the advantages of light energy collection technology. In this study, an ion diode moisture-based power generation array was fabricated to yield an open-circuit voltage of 8 V and a short-circuit current of 3 mA under an 86.9% relative humidity (RH). Subsequently, integration of a photovoltaic module with the hygroelectric generator assembly via an energy management circuit augmented the system's overall power generation, manifesting a remarkable 1150% increase over the original moisture-based power generation configuration. Furthermore, the incorporation of such a hybridized system bolstered the operational efficiency, extending the duration of continuous power supply cycles by up to 78.2% in comparison with the control group with no moisture-derived energy input. This pioneering endeavor unveils a novel light-moisture coupling energy-harvesting paradigm tailored for sustaining uninterrupted power provision in wireless sensor network nodes, and the harvesting of one energy source is not affected by the other energy source at all. With its inherent adaptability, this approach holds promise for deployment in outdoor environments characterized by low illumination levels and high humidity, presenting a versatile solution to address sensor powering challenges.

An image enhancement based method for improving rPPG extraction under low-light illumination

Remote photoplethysmography (rPPG) has gained significant attention as a non-invasive approach for measuring human vital signs from videos. However, the reliance on capturing the reflection of ambient lighting causes it to be susceptible to the adverse effects of low illumination levels, leading to deterioration in the signal quality. The preliminary study introduces a novel methodology for enhancing rPPG signal extraction in low-light conditions through the integration of an Image Enhancement Model (IEM) inspired by Retinex theory, which significantly improved signal quality by preprocessing video frames to better capture the subtle changes in facial blood flow. Recognizing the challenge posed by the generalization capacity over different deep-learning models and unseen examples from various datasets, this study further evaluated the efficacy of the IEM + rPPG extraction model across multiple datasets (UBFC-rPPG, BH-rPPG, MMPD-rPPG, and VIPL-HR) by integrating IEM with existing deep-learning based rPPG extraction models including DeepPhys, PhysNet, and PhysFormer and traditional POS rPPG extraction method. Our experiments demonstrate a consistent improvement for all the methods in heart rate estimation accuracy across all datasets, underscoring the IEM’s adaptability and effectiveness. The paper also explores the application of our method to traditional rPPG extraction techniques, further validating its potential for broader usage. Through comprehensive analysis, this research not only confirms the impact of lighting conditions on rPPG signal quality but also provides a robust solution for more reliable non-invasive vital sign monitoring in diverse environments.

TSRNet: A Trans-Scale and Refined Low-Light Image Enhancement Network

Retinex-based deep learning methods show good low-light enhancement performance and are mainstream approaches in this field. However, the current methods for enhancing low-light images are insufficient in accurately separating illumination and comprehensively restoring degraded information, especially in images with uneven or extremely low illumination levels. This situation often leads to the over-enhancement of bright regions, a loss of detail, and color distortion in the final images. To address these issues, we improved three subnetworks in the classic KinD network, and proposed a trans-scale and refined low-light image enhancement network. Compared with KinD, our method shows more precise image decomposition performance, enhancing the expressiveness of the reflection and illumination components in order to better depict image details, colors, and lighting information. For reflectance restoration, we use a U-shaped network for cross-scale denoising, incorporating attention mechanisms and a color saturation loss to restore image textures and colors. For light adjustment, we apply fine-grained light adjustment approaches to simultaneously enhance brightness in dark areas and prevent excessive enhancement in bright areas. The experimental results demonstrate that with the LOL dataset, the peak signal-to-noise ratio (PSNR) and structural similarity index measure (SSIM) of TSRNet are improved by 2–31% and 5–34%, respectively, when compared with the mainstream methods.

Indoor Environmental Quality Assessment of Train Cabins and Passenger Waiting Areas: A Case Study of Nigeria

The adequacy of the indoor environmental quality (IEQ) in mass transit microenvironments is crucial to the well-being of exposed commuters. By 2050, many developing tropical countries will host even more megacities, which will feature an increase in people mobility and higher occupancy density. The paucity of IEQ studies, the technology gap, and inadequate policy measures to assure safer and sustainable mobility in many developing tropics have reinforced the current study objective. Also, the recent COVID-19 pandemic has highlighted the IEQ links and risks to health in transport, which, given the climate peculiarities, transport reforms, and huge commuter traffic in Nigeria, inform the study motivation. The indoor air quality (CO2, PM, VOCs, NO2), thermal, acoustic, and visual environments were objectively assessed in train passenger cabins and waiting areas, during 15 trips in the dry and rainy seasons in Nigeria. The results were analyzed by following the IEQ requirements defined in the ISO, CEN, ASHRAE, and SAE standards. The results indicate gaps in the IAQ (inadequate ventilation in 9 trains), defective thermal comfort (9 trains), exceedance in the PM limit (PM10: 47.9–115 μg/m3, PM2.5: 22.5–51.3 μg/m3), noise (Leq range: 64–85 dBA), and low illuminance levels (10 trains), hence the need for IEQ, interventions, stakeholder awareness, and broader IEQ studies on transport cabins in these regions.

Variation of Ambient Illumination Across Different Locations: An Impact on Antimyopia Strategy

PURPOSE: To evaluate whether the level of ambient illumination in winter at different locations, time of a day, sun protection, and source position remains optimum (≥1000 lux) for controlling myopia progression. METHODS: Illuminance level was recorded for 6 outdoor and 5 indoor locations using factory calibrated digital lux meter and under different measurement conditions. Outdoor locations included “open playground,” “between two buildings,” “between three buildings,” “under a porch facing east,” “under a big tree,” and “under a porch facing west.” Similarly, indoor locations included “rooms with multiple large windows,” “rooms with a combination of light sources,” “room with single artificial light,” “room with multiple artificial lights,” and “canopy covering the buildings.” RESULTS: The overall median illumination level across 6 outdoor locations and 5 indoor locations were 1900 lux (803–4300 lux) and 227 lux (82–556 lux) respectively. Indoor locations showed an overall low median illuminance level (<1000 lux) irrespective of the locations and source positions. However, the illuminance level >1000 lux was recorded for “Room with multiple large windows” for specific points of time (10:00–11:00 and 13:00–14:00) in both sunny and foggy weather. The highest illumination level was recorded only in the “open playground” irrespective of various conditions such as time of the day, weather of the day, relative source position, and sun protection. CONCLUSION: The ambient illumination level was optimum (≥1000 lux) for antimyopia strategy in winter for maximum outdoor locations. However, children should be motivated to spend their outdoor time during the afternoon (13:00–14:00 h) so that light intensities reaching the eye should be optimum in winter.

Characterization of a small amorphous photovoltaic panel and derivation of its SPICE model

This paper presents a simple method to resolve the parameters of the single-diode equivalent circuit for small amorphous photovoltaic (PV) panels. It is based on a precise measurement using a test bench that allows the characterization of PV panels at different illumination levels from 10 lx to 3000 lx. The measurement under different illumination conditions allows the calculation of the model parameters using only a standard polynomial, logarithmic and exponential functions - no numerical approach or Lambert W function is required. The solved parameters are later used in LTspice simulations, which are compared with the real measurements. The Spice model presented in this paper is based on the single diode model, but is modified to be more reliable at low illumination levels. The Spice model can be used for the design of MPPT systems or for various indoor IoT applications, where it allows to predict the available energy under different conditions.

Assessing the performance of façade-integrated transparent photovoltaic panels for daylight and energy generation in high rise buildings of hot & dry climate

Indian cities are witnessing a boom in the growth of high-rise buildings to accommodate the ever-intensifying population. The modern trend of applying glass on the façades of tall buildings holds a threat due to Indian climates. Though it allows the daylight, reduces the artificial lighting, and provides a good view, the heat gained through the glass façades increases a building’s energy consumption. Therefore, an innovative, advanced strategy is required that replaces the glass with alternatives which can potentially minimize the energy demands either by controlling the heat gain or producing the electricity by itself, to match the demand. Transparent photovoltaic facades can ideally solve this purpose, as it allows the daylight and are multi-functional in nature. It produces electricity and fulfils several other tasks of solar protection and glare protection. But, the presence of solar cells may cause undesirable shading or low illuminance levels; hence, it is important to comprehensively assess the daylight performance and also calculate its energy performance. The aim of the current research paper is to determine the effectiveness of integrating the transparent photovoltaic panels over window/glass façades of daytime-occupied high-rise buildings in a Hot & dry climate and the form configurations required to achieve a considerable amount of energy on-site, without affecting the quantity of daylight. In this study, the performance of the amorphous silicon (a-Si) PV window, with 26.7% visibility, was evaluated through simulation using Rhino+Honeybee software over different building sizes & aspect ratios. The results showed that there was a gradual decline in the energy intensity with increase in length and the energy intensity got increased with an increase in floor height. The form with a high aspect ratio had the highest EPI of 228kwh/m2/year. Further, the form with the least aspect ratio achieved a better daylight performance. The findings of this research are potentially valuable for building designers and decision-makers to foresee the behaviour pattern of BIPV facades in energy generation, while affirming a comfortable and luminous environment.

Effect of Low Light Stress on Distribution of Auxin (Indole-3-acetic Acid) between Shoot and Roots and Development of Lateral Roots in Barley Plants.

Depending on their habitat conditions, plants can greatly change the growth rate of their roots. However, the mechanisms of such responses remain insufficiently clear. The influence of a low level of illumination on the content of endogenous auxins, their localization in leaves and transport from shoots to roots were studied and related to the lateral root branching of barley plants. Following two days' reduction in illumination, a 10-fold reduction in the emergence of lateral roots was found. Auxin (IAA, indole-3-acetic acid) content decreased by 84% in roots and by 30% in shoots, and immunolocalization revealed lowered IAA levels in phloem cells of leaf sections. The reduced content of IAA found in the plants under low light suggests an inhibition of production of this hormone under these conditions. At the same time, two-fold downregulation of the LAX3 gene expression, facilitating IAA influx into the cells, was detected in the roots, as well as a decline in auxin diffusion from shoots through the phloem by about 60%. It was suggested that the reduced emergence of lateral roots in barley under a low level of illumination was due to a disturbance of auxin transport through the phloem and down-regulation of the genes responsible for auxin transport in plant roots. The results confirm the importance of the long distance transport of auxins for the control of the growth of roots under conditions of low light. Further study of the mechanisms that control the transport of auxins from shoots to roots in other plant species is required.

The effect of filters and varying illumination on contrast sensitivity in eyes with moderate to severe visual impairment.

To investigate the effect of filters and illumination on contrast sensitivity in persons with cataract, pseudophakia, maculopathy and glaucoma to provide a guide for eye care providers in low vision rehabilitation. A within-subjects experimental design with a counter-balanced presentation technique was employed in this study. The contrast sensitivity of eyes with cataract, pseudophakia, maculopathy and glaucoma was measured with filters (no filter, yellow, pink and orange) combined with increasing illumination levels (100lx, 300lx, 700lx and 1000lx) using the SpotChecks™ contrast sensitivity chart. The data were analyzed using descriptive statistics and two-way repeated measures ANOVA. The yellow filter at 100lx significantly improved contrast sensitivity in the maculopathy group. There were no significant improvements with either intervention in the rest of the groups. There was, however, a significant interaction between filters and illumination in the cataract group. There were small improvements in contrast sensitivity at low illumination levels with the yellow filter in the maculopathy group, and this could be considered in clinical practice and low vision rehabilitation. Overall, filters at most illumination levels did not benefit most groups.

Road lighting and mesopic vision

Human beings perceive information from the environment by using their sense organs. Vision is believed to provide the most information. There are three categories of vision: scotopic, mesopic, and photopic vision. The activity of two types of light-sensitive receptors in the eye, cones and rods, is different for each category. Cones and rods have a unique ability to adapt to different levels of illumination. Adaptation is the ability of the human eye to adapt to changing lighting conditions. Thanks to this mechanism, the human visual system has the ability to operate in a very wide range of pupil illuminations, that is, at different adaptive levels. At very low adaptive levels, only the rods are active, and the vision is called scotopic. As adaptive levels increase, starting at 0.005 cd/m2, the rods become less active, meanwhile the cones become active, and then the vision is called mesopic. At adaptive levels above 5 cd/m2, only cones are active, and the vision becomes photopic. Cones and rods have different spectral sensitivities: rods are more sensitive to short wavelengths, while cones are most sensitive within the visible spectral range. Cones are concentrated mainly in the part of the retina of the eye that is used for direct (on-line) vision, while rods are localized only in the areas used for peripheral vision. As a result, in case of mesopic vision, the peripheral vision becomes better with light sources that have a relatively large component of short wavelengths. The same is true for the subjective perception of brightness. At low adaptation levels, more rods become active, and thus these benefits are greater at low illumination levels.
 Since photometric units are based on photopic vision, these advantages are not obvious. Thus, the correction factors should be determined according to the spectrum of light sources, which is characterized by the S/P ratio, and the illumination levels of road lighting.
 The International Commission on Illumination has prepared a standard (CIE 115:2010 Lighting of roads for motor and pedestrian traffic). The main goals of road lighting are to ensure visual performance, visual comfort and to keep drivers alert.

Strange-face-in-the-mirror illusions: specific effects on derealization, depersonalization, and dissociative identity

ABSTRACT Anomalous strange-face illusions (SFIs) are produced when mirror gazing under a low level of face illumination. In contrast to past studies in which an observer’s task was to pay attention to the reflected face and to perceive potential facial changes, the present research used a mirror gazing task (MGT) that instructed participants to fixate their gaze on a 4-mm hole in a glass mirror. The participants’ eye-blink rates were thus measured without priming any facial changes. Twenty-one healthy young individuals participated in the MGT and a control panel-fixation task (staring at a hole in a gray non-reflective panel). The Revised Strange-Face Questionnaire (SFQ-R) indexed derealization (deformations of facial features; FD), depersonalization (bodily face detachment; BD), and dissociative identity (new or unknown identities; DI) scales. Mirror-fixation increased FD, BD, and DI scores compared to panel-fixation. In mirror-fixation, FD scores revealed fading specific to facial features, distinct from “classical” Troxler- and Brewster-fading. In mirror-fixation, eye-blink rates correlated negatively with FD scores. Panel-fixation produced low BD scores, and, in a few participants, face pareidolias as detected on FD scores. Females were more prone to early derealization and males to compartmentalization of a dissociative identity. SFQ-R may be a valuable instrument for measuring face-specific dissociation (FD, BD, DI) produced by MGT. Use of MGT and panel-fixation task for differential diagnoses between schizophrenia and dissociative identity disorder is discussed.

Lighting environmental assessment in enclosed spaces based on emotional model

Lighting assessment in special operating environments like enclosed spaces is of great research significance and value. In addition to investigating the visual ergonomics of workers, the emotional monitoring and guidance of workers in enclosed spaces is also a research focus. Based on the Circumplex emotion model theory, this paper designs an experiment to assess emotions in an enclosed space with 6 different lighting settings (2 correlated color temperature (CCT) × 3 illuminance levels). From the perspective of subjective assessment, participants used a rapid sensory analysis method (Check-all-that-apply, CATA) and a Subjective Coordinate Scale (SCS) method for rapid ambience perception checking and emotional self-reporting of lighting settings. From the perspective of objective evaluation, the participants' facial expressions were recorded during the experiment using a camera, and then the recorded facial expressions were automatically analyzed and predicted using FaceReader (FRE) software. The CATA and SCS showed similar results, with the 3100 K × 600 lx, 3100 K × 1000 lx and 6500 K × 600 lx lighting settings creating a relaxed, pleasant emotion in participants, the 6500 K × 1000 lx setting creating an excited, tense atmosphere, and the low illumination level settings of 3100 K × 250 lx and 6500 K × 250 lx made participants feel tired and frustrated. The results of the objective emotion analysis indicate that the FRE was able to effectively identify differences in participants' emotions in response to different lighting settings and was consistent with the results of participants' subjective emotion reports. This laboratory study validates that the three methods can effectively assess the enclosed space lighting settings, and provides a reference for further research on the enclosed space lighting settings and emotional monitoring of workers in the future.

Integration of a superconducting nanowire detector into a confocal microscope for TRPL-mapping: Sensitivity and time resolution.

Superconducting Nanowire Single Photon Detectors (SNSPDs) were introduced to the market in 2003 and are used in multiple quantum optics applications, due to their outstanding properties such as fast instrument response and high quantum efficiency. The high quantum efficiency is important for materials science applications with emission in IR-range >1000 nm, where other available single photon detectors have a low sensitivity, high dark noise, and slow time response. We have integrated a SNSPD (Single Quantum) into a confocal photoluminescence lifetime microscope MicroTime 100 (PicoQuant) in order to compare the performance of different SNSPD designs with a standard IR-PMT for time-resolved photoluminescence (TRPL) measurements and imaging of IR sample e.g., CIGS device. One used SNSPD channel was a classical single mode fiber coupling to guide the light onto the sensor, the other channel used an internal multimode fiber instead. We achieved a significant increase in photoluminescence sensitivity in both designs compared to a standard IR-PMT, as well as a several times higher sensitivity of the multimode-fiber coupled nanowire compared to the singe-mode fiber one, despite comparable photon quantum efficiencies in this wavelength range. The increased sensitivity combined with the lower dark count rate resulted in an increase of signal-to-noise ratio by more than 2 orders of magnitude compared to the IR-PMT. The high sensitivity of SNSPDs combined with high temporal resolution (instrument response function of this setup was below 100 ps) allows to identify and investigate highly quenched signals of samples even at low illumination levels. The integration of the SNSPD detector to a scanning confocal microscope will also enhance the capabilities in field of single oxygen sensing and cell imaging in NIR by using NIR emitting dyes or nanoparticles without autofluorescence.

Physiological state of chickens cross dekalb white depending on the conditions of detention

The functional state of the heart, liver and kidneys of Dekalb White cross chickens kept for 13 weeks under different light conditions was assessed. The study was carried out in the Department of Аnimal Husbandry and Poultry Federal State Budgetary Scientific Institution Far East Zone Research Veterinary Institute and Department of Physiology and Pathophysiology FSBEI HE Amur SMA MOH Russia, Blagoveshchensk, Amur region, Russia. In the conditions of the Belogorskaya poultry farm of the Amur region, chickens were kept in cell batteries from the age of 3 weeks at standard (6-10 lux) and brighter (40-50 lux) illumination. During the experiment, laboratory diagnostics of the blood of birds aged 4, 9, 12 and 16 weeks was carried out. 60 young laying hens aged 16 weeks were taken for anatomical examination, macro- and micromorphological examination of the heart, liver and kidneys was performed. It was revealed that at a low level of illumination (6-10 lux), the amount of hemoglobin in the blood of chickens decreased by 5,5-12,5% and erythrocytes by 4,2-15,5%, from 9 weeks of age, the amount of glucose decreased by 29,7% compared to the norm with an increase in the level of gamma globulins by 17,4-48,2%, bilirubin by 2,9 times, aspartate aminotransferase by 2,5 times, alanine aminotransferase by 2,2 times, creatinine by 63,7% higher than normal, at 16 weeks of age, an increase in absolute weight right ventricle of the heart by 4,5%, interventricular septum by 22,2%, epicardial fat by 11,0% and abdominal fat by 17,4%. In chickens with illumination of 40-50 lux, the established deviations were less significant, microscopy showed an increase in the area of the lumen of the arterial vessels by 27,1% in the myocardium and 5,7% in the hepatic lobules, a decrease in the area of the juxtamedullary glomeruli by 5,9%, the area of the lumen of the proximal and distal tubules of nephrons by 8,6-33,7%, indicating an improvement in the functional state of the heart, liver and kidneys.

HyU: Hybrid Unmixing for longitudinal in vivo imaging of low signal-to-noise fluorescence

The expansion of fluorescence bioimaging toward more complex systems and geometries requires analytical tools capable of spanning widely varying timescales and length scales, cleanly separating multiple fluorescent labels and distinguishing these labels from background autofluorescence. Here we meet these challenging objectives for multispectral fluorescence microscopy, combining hyperspectral phasors and linear unmixing to create Hybrid Unmixing (HyU). HyU is efficient and robust, capable of quantitative signal separation even at low illumination levels. In dynamic imaging of developing zebrafish embryos and in mouse tissue, HyU was able to cleanly and efficiently unmix multiple fluorescent labels, even in demanding volumetric timelapse imaging settings. HyU permits high dynamic range imaging, allowing simultaneous imaging of bright exogenous labels and dim endogenous labels. This enables coincident studies of tagged components, cellular behaviors and cellular metabolism within the same specimen, providing more accurate insights into the orchestrated complexity of biological systems.

Design and Performance Test of Low Light Level Illumination Source with Wide Dynamic Range

Design and Performance Test of Low Light Level Illumination Source with Wide Dynamic Range

Obtaining new types of compounds between silicon and cadmium sulfide

The n+CdS-nCdS-nSi+ structures were obtained and their volt-ampere characteristics at different temperatures were studied. From the dependence of the volt-ampere characteristic it is shown that the sublinear and quadratic section of these structures has a section of current growth with voltage. It is determined that the n+CdS-nCdS-nSi+structures in the current flow direction at low illumination levels work as an injection photodiode. And these structures under laser illumination with λ=0.625 μm and power P=1.2 μW/cm2 have spectral sensitivity 2042 A/W, bias voltage 10 V. At irradiation by white light with energy W=3.6-10μW∙s it has integral sensitivity ≈21 A/I’m (2310 A/W) at bias voltage U=10V.

Obtaining new types of compounds between silicon and cadmium sulfide

The n+CdS-nCdS-nSi+ structures were obtained, and their volt-ampere characteristics at different temperatures were studied. The dependence of the volt-ampere characteristic shows that the sublinear and quadratic section of these structures has a section of current growth with voltage. It is determined that the n+CdS-nCdS-nSi+ structures in the current flow direction at low illumination levels work as an injection photodiode. And these structures under laser illumination with λ=0.625 μm and power P=1.2 µW/cm2 have spectral sensitivity 2042 A/W, bias voltage 10 V. At irradiation by white light with energy W=3.6-10µW·s it has integral sensitivity ≈21 A/I'm (2310 A/W) at bias voltage U=10V.

Bioethanol to Hydrogen Membrane Surface Characteristics Change Study

The problem of the gradual transformation of the modern economy towards greater production and consumption of ‘green’ energy requires a significant revision of existing technologies. One of the possible ways to develop green energy is the use of hydrogen as the most environmentally friendly fuel. Hydrogen can be obtained both by electrolysis, using solar energy, and using biorenewable raw materials, which can be used as ethanol, biogas, peat, agricultural waste. At the same time, for regions with a low level of illumination, the production of hydrogen by electrolysis of water using electricity generated by solar panels is inaccessible, and therefore the processing of biorenewable raw materials can take a leading position. Bioethanol is a large-capacity product with a proven production technology that widely uses waste from agriculture and wood processing. Ethanol can be used as a feedstock for hydrogen generation by means of catalytic pyrolysis or catalytic steam reforming. Membrane-catalytic steam reforming of ethanol with the production of hydrogen makes it possible to obtain hydrogen without the use of an additional purification step, however, the efficiency and stability of the membrane becomes the determining parameter that ensures the efficiency of the entire process. The degradation of inorganic membranes during catalytic steam reforming is closely related to the change in porosity as a result of hydrolysis of the membrane surface. In this connection, the study of the physicochemical properties of membranes during operation can make a significant contribution to the development of stable catalytic membranes for hydrogen production. The article presents the results of studying the physicochemical properties of an inorganic membrane for ethanol steam reforming by the method of low-temperature nitrogen adsorption. The Langmuir, Brunauer-Emmett-Taylor, t-plot and Barrett-Joyner-Halenda models were used to estimate the surface change. An increase in the surface area of mesopores during the operation of the membrane was determined.

Saturation of visual responses explains size tuning in rat collicular neurons.

The receptive field of many visual neurons is composed of a central responsive area, the classical receptive field, and a non-classical receptive field, also called the "suppressive surround." A visual stimulus placed in the suppressive surround does not induce any response but modulates visual responses to stimuli within the classical receptive field, usually by suppressing them. Therefore, visual responses become smaller when stimuli exceed the classical receptive field size. The stimulus size inducing the maximal response is called the preferred stimulus size. In cortex, there is good correspondence between the sizes of the classical receptive field and the preferred stimulus. In contrast, in the rodent superior colliculus, the preferred size is often several fold smaller than the classical receptive field size. Here, we show that in the rat superior colliculus, the preferred stimulus size changes as a square root of the contrast inverse and the classical receptive field size is independent of contrast. In addition, responses to annulus were largely independent of the inner hole size. To explain these data, three models were tested: the divisive modulation of the gain by the suppressive surround (the "normalization" model), the difference of the Gaussians, and a divisive model that incorporates saturation to light flux. Despite the same number of free parameters, the model incorporating saturation to light performed the best. Thus, our data indicate that in rats, the saturation to light can be a dominant phenomenon even at relatively low illumination levels defining visual responses in the collicular neurons.