Illuminance Measurements Research Articles

The Role of Standard and Supplementary Observers in Accurate Illuminance measurements

Typically the sensitivity V2 (λ) for a 2° standard observer is used at photometric measurments. Nevertheless, the light reach the human eye from wider field of view. This fact motivated the International Commission on Illumination to introduce the 10° supplementary observer with sensitivity V10 (λ). This paper analyzes the impact of transition from V2 (λ) to V10 (λ) on measured pc-LEDs illuminance values. The results indicate that the maximum difference is 2% for 3000 K pc-LEDs, 4% for 4000 K pc-LEDs, and 6% for 6500 K pc LEDs. Full Text: PDF References K.S. Gibson, E.P.T. Tyndall, "Visibility of Radiant Energy", Scientific Papers of the Bureau of Standards, 19, 131 (1923). CrossRef E.P. Hyde, W.E. Forsythe, F.E. Cady, J. Frank. "The visibility of radiation", Inst. 185, 829 (1918). CrossRef I. Fryc, M. Listowski, R. Supronowicz, "Going beyond the 20th century color space to evaluate LED color consistency", Opt. Express 31(23), 38666 (2023). CrossRef R. Supronowicz, J. Fan, M. 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Gignac, "Design of Glass Filter Combinations for Photometers", Appl. Opt. 8, 2449 (1969). CrossRef S. Winter, D. Lindner, A. Sperling, G. Sauter, S. Brown, T. Larason, Y. Zong, Y. Ohno, Proceedings of the 9th International Conference on New Developments and Applications in Optical Radiometry (NEWRAD), Davos, 2005. DirectLink I. Fryc, P. Tabaka, "The influence of different photometric observers on luxmeter accuracy for LEDs and FLs lamps measurements", Opt. Appl. XLIX, 345 (2019). CrossRef U.S. Energy Information Administration, Commercial Buildings Energy Consumption Survey (2021). DirectLink United Nations Environment Programme (2013). Minamata convention on mercury: text and annexes, (2013). DirectLink M. Listowski, R. Supronowicz, "Color quality consideration when switching from FL to LED", Photonics Lett.Pol. 14, 56 (2022). CrossRef J. Cho, J.H. Park, J.K. Kim, E.F. Schubert, "White light-emitting diodes: History, progress, and future", Phot. Rev. 11, 1600147 (2017). CrossRef K. 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Ultraviolet radiation from solariums: the main problems of measurement and evaluation of results

Introduction. Artificial tanning is now considered a public health issue. There is strong evidence linking tanning bed use to the risk of skin cancer. One measure to reduce the health risks associated with artificial tanning is to control exposure to ultraviolet radiation (UVR). Assessing the compliance of UV solariums with hygienic standards requires solving two main problems – methodological and instrumental support for the measurements taken. The purpose of the study was to substantiate methodological approaches to measuring UVR irradiance in solariums. Material and methods. Regulatory and methodological documents, as well as literary sources devoted to the issues of conducting UVR measurements of solariums and the criteria for assessing their compliance, were analyzed. To justify the conditions and scope of research, measurements of the energy illumination of the UVR of a mini-solarium, and pilot studies in a vertical turbo solarium using a UV Radiometer were carried out. Results. According to the results of UVR measurements at the minimum possible distance from the radiating block of the mini-solarium, the highest values ​​of energy illumination in all ranges were obtained at the central point, which was also confirmed by the results of scanning the radiating surface. Analysis of the research results in a vertical turbo solarium at a distance of 0.3 m from the central vertical axis of the solarium showed that the highest values ​​of energy illumination for the two blocks were obtained at different heights (1.0 m and 0.5 m from the supporting surface), which confirms the need to carry out measurements at several points along the height of each radiating block. Limitations. The results of the study can only be used when measuring the irradiance of ultraviolet radiation in solariums using UV radiometers. Conclusion. The proposed methodological approaches make it possible to measure the energy illumination of ultraviolet radiation in places where solariums are used, process and format of the results obtained, and evaluate them for compliance with current hygienic standards. Issues arised when carrying out measurements and assessing energy illumination in the spectral region of 200–400 nm when examining solariums are identified.

Design and Application Research of a UAV-Based Road Illuminance Measurement System

This paper presents a UAV-based road illumination measurement system and evaluates its performance through experiments. The system employs a HUBSAN Zino 2+ UAV, STM32F103RCT6 microcontroller, BH1750 illuminance sensor, and GPS and integrates flight, processing, measurement, cloud platform, obstacle avoidance, communication, and power supply units via the OneNET cloud platform. Both hardware and software designs were implemented, using the Z-score algorithm to handle outliers in illumination data. The system showed a single-point measurement error rate of 1.14% and a MAPE of 5.08% for multi-point measurements. In experiments, the system’s horizontal and vertical illuminance RMSE were 1.92 lx and 1.75 lx, respectively. The real-time visualization interface improved operational efficiency, cutting labor costs by half and time costs by nearly four-fifths. UAV control and monitoring from the roadside ensured safety during measurements. The system’s efficiency and wide measurement range enabled extended experiments, collecting illuminance data across multiple horizontal and vertical planes. This resulted in the creation of both horizontal and innovative vertical-plane illuminance distribution maps. These findings provide valuable data for evaluating road lighting quality, enhancing road traffic safety, and improving road illumination design.

Optimal placement of light sensor for improving energy efficiency and visual comfort in smart buildings

The energy consumed by artificial lighting accounts for a significant part of the energy consumption in buildings. Thus, energy consumption can be significantly decreased using optimization techniques, such as the optimum placement of the lighting sensors. In this paper, an optimal placement method of the light sensors is presented to minimize the lighting system's equipment costs and energy consumption and also meet visual comfort under the requirements of the European standard EN12464–1 regarding illuminance-based criteria. In the beginning, based on the illumination measurement grid's mathematical model, the potential location of the sensors is determined. As an average of the dimming levels of the LED lights, the objective function has been introduced. Then, the illuminance and uniformity levels are defined as constraints for the optimization problem. The Battle Royale Optimization (BRO) algorithm is used to solve the optimization problem. Ultimately, based on the results of the BRO algorithm and the calculation of the illuminance deviation, the optimal location of the light sensors is determined. The proposed method is tested in an office room. A fuzzy logic controller is developed to regulate the lighting control system's dimming levels to evaluate the proposed method's performance with other approaches. The comparison results have shown that the proposed method is superior as regards the number of sensors and the optimal sensor position, significant savings in energy consumption of up to 30.8%, and satisfactory visual comfort per the requirements of the European standard EN12464–1.

Effects of high-speed rail illumination on traffic safety at night in a road-cum-railway section – Implications for the infrastructure design

Intense light from trains can cause glare, affecting the driving safety of vehicles running in the opposite direction at road-cum-railway sections. This study, in particular, examines glare impacts caused by high-speed rail (HSR) illumination on highway traffic driving safety in a road-cum-railway bridge. Field surveys and tests are conducted on the illumination measurement for HSR, and disability and discomfort glare are investigated and quantified, with parameters being calibrated. A simulation-based platform is established and utilised to explore the impacts of HSR illumination on road traffic safety under different horizontal distances and traffic volumes. Different traffic safety risk indicators are utilised to evaluate traffic safety, including time-to-collision (TTC) and weight integrated risk level (WIRL). The results demonstrate that glare, especially disability glare, significantly increases traffic safety risks. The traffic safety of multi-axle vehicles are more negatively affected. The negative effect appears to strengthen with increasing traffic flows and decline with increasing horizontal distance between the high-speed railway and the highway. Anti-glare light barrier installation is an effective way to eliminate the negative effects and appropriate heights of anti-glare barriers are suggested for different horizontal distances.

Temperature-Dependent Photoluminescence from Well-Resolved Excited State Structures in Rare-Earth-Based Double Perovskites.

Lead-free halide double perovskites (DPs) have become a research hotspot in the field of photoelectrons due to their unique optical properties and flexible compositional tuning. However, the reports on the optical properties of DPs primarily concentrate on the room temperature state and only exhibit single emission band. Here, we synthesized Cs2NaYCl6:Sb3+, Dy3+ DPs by a solvothermal method to realize white light emission with photoluminescence (PL) quantum yield as high as 70.7%. The energy-transfer process from self-trapped excitons (STEs) to Dy3+ ions was revealed by optical characterization and theoretical simulation calculations. Interestingly, we observed the double-emission from low-energy STE emission of Sb3+ ions and Dy3+ emission at low temperatures, and the double-emission is consistent with the asymmetric doublet feature of the 3P1 → 1S0 transition split into two minima. The PL spectra further showed that the fluorescence intensity ratios of Dy3+ ions at 580 and 680 nm were strongly temperature-dependent, and the relative sensitivity is up to 1.79% K-1 at 360 K. Moreover, the near-infrared and radiation luminescence properties indicated that the Cs2NaYCl6:Sb3+, Dy3+ DPs also have good prospects for night vision and radiation detection, as well as the great potential for applications in solid-state illumination and optical temperature measurement.

Replacement of tubular fluorescent lamps with tubular LEDs lamps and daylight integration in classrooms and laboratories

The quality of lighting significantly influences our ability to perform tasks in enclosed spaces, and certain characteristics of lighting sources play a crucial role. Light-emitting diode (tubular LED) lamps offer advantages for both home and office use. Choosing tubular LED lamps over fluorescent ones is beneficial for several reasons. Tubular LEDs are mercury-free, ensuring environmental safety compared to the small amount of mercury present in fluorescent tubes. Furthermore, tubular LEDs provide directional lighting, minimizing light loss in fixtures and unnecessary areas, and offering better efficiency (around 40% more than tubular fluorescent lamps). Also, they produce high-quality light with various color temperatures, eliminating flickering issues that can cause discomfort such as eye strain, headaches, and migraines. Additionally, tubular LEDs have a longer lifespan making them a preferable lighting option. The superior quality of natural light makes it the optimal source of illumination, which matching well with the visual response of the human eyes. Daylight has a positive influence on people, instilling a feeling of vibrancy and brightness within their living environment. The acknowledged benefits of daylight extend to enhancing visual comfort, promoting health, and improving overall performance among building occupants. This paper focuses on the integration of natural daylight with artificial light, particularly through tubular LED lamps, and investigates the daylight factor. Two groups of six tubular LED lamps (60cm with 9 Watt and 120cm with 18 Watt) and another group of six tubular fluorescent lamps (60cm with 18 Watt and 120cm with 36 Watt) were studied. The study involved two sets of six tubular LED lamps (60cm with 9W and 120cm with 18W) and another set with six tubular fluorescent lamps (60cm with 18W and 120cm with 36W). Measurements were conducted using Spectroradiometer Ocean Optics HR 2000 with 4.7% uncertainty and a photometric bench to assess the spectral output. Additionally, UVA/B silicon detector and Luxmeter detector setups with uncertainties of 5.2% and 6%, respectively, were employed for irradiance and illuminance measurements of tubular LEDs and fluorescent lamps. Various parameters, including daylight factor ratio, UVA power to luminous flux (K) for tubular fluorescent lamps, spectral power distribution, and illumination levels were obtained. Integration between daylight and tubular LED lamps was also determined. The maximum detected value lmW /013.0  is less than the safe limit for human health but still there are effects on human health if they use these types of lamps. Therefore, it is advisable to switch from tubular fluorescent lamps to tubular LEDs to mitigate the impact of UVA on human health and the environment.

Illumination matters Part II: advanced comparative analysis of flexible ureteroscopes in a kidney model by PEARLS

PurposeThe aim of the study was to evaluate illumination properties in an in-vitro kidney calyx model in saline.Design and methodsWe evaluated a series of contemporary flexible ureteroscopes including the Storz Flex-Xc and Flex-X2s, Olympus V3 and P7, Pusen 7.5F and 9.2F, as well as OTU WiScope using a 3D-printed closed pink kidney calyx model, submerged in saline. A spectrometer was used for illuminance and color temperature measurements at different openings located at center (direct light), 45° (direct and indirect light) and 90°(indirect light) to the axis of the scope.ResultsMaximum illuminance was at the center opening for all scopes (range: 284 to 12,058 lx at 50% brightness and 454 to 11,871 lx at 100% brightness settings). The scope with the highest center illuminance (Flex-Xc) was 26 times superior to the scope with the lowest illuminance (Pusen 7.5Fr) at 100% brightness setting. For each scope, there was a peripheral illuminance drop ranging from − 43 to − 92% at 50% brightness and − 43% to − 88% at 100% brightness settings, respectively (all p < 0.01). Highest drop was for the P7 and the Pusen 9.2F. All scopes had illuminance skew, except the V3. All scopes had a warm color temperature.ConclusionIllumination properties vary between ureteroscopes in an enclosed cavity in saline, and differs at center vs 45° and 90° positions within scopes. Peripheral illuminance drop can be as high as − 92%, which is undesirable. This may affect the choice of ureteroscope and light brightness settings used in surgery by urologists.

Illumination matters Part III: Impact of light obstruction on illuminance from flexible ureteroscopes — a comparative PEARLS analysis

PurposeArtifacts from poor ureteroscopes’ light design with shadowing and dark areas in the field of view have been reported. The aim was to quantify effects of light obstruction in a kidney calyx model.MethodsWe evaluated a series of contemporary flexible ureteroscopes including the Storz Flex-Xc and Flex-X2s, Olympus V3 and P7, Pusen 7.5F and 9.2F, as well as OTU Wiscope using an enclosed 3D-printed pink in vitro kidney calyx model submerged in saline, where the field of light was intentionally partially obstructed alternatively at 12, 3, 6, and 9 o’clock. A color spectrometer was used for illuminance measurements at a 45° opening position in the background of the model.ResultsOverall and mean background illuminance for each obstructive situation were significantly different between scopes for both 50% and 100% brightness settings (ANOVA p < 0.001). At 50% brightness setting, almost all scopes had their highest and lowest background illuminance with the 6 o’clock and 3 o’clock obstructive situation, respectively. At 100% brightness setting, these became 6 o’clock and 12 o’clock obstructive situations. Considering each obstructive situation individually, the Flex-Xc was consistently the scope with highest background illuminance and the Pusen 7.5F the lowest. Background illuminance for each obstructive situation varied significantly for each scope individually, with the greatest range of variability for Pusen 7.5F and V3.ConclusionsIlluminance performance of ureteroscopes within an obstructed calyx model differ significantly for various obstructive situations. Urologists should be aware of this to help guide their choice of ureteroscope.

Assessment of the visibility of unprotected road users in pedestrian crossing

The article presents selected results of research on improving pedestrian traffic safety. Based on annually-updated accident statistics made available by the police, as well as the new pedestrian traffic regulations in force, detailed work was undertaken to assess the level of visibility of pedestrians by drivers in pedestrian crossing areas. The research was carried out by analyzing several characteristic cases of pedestrian crossings occurring in Poland, in which there was only dedicated lighting for crossings, only street lighting, and a variant of coexistence of both of the above lighting solutions. Illuminance measurements were made in the horizontal and vertical planes of pedestrian crossings, and the results were confronted with the relevant guidelines. The next step involved a complementary measurement of the luminance distribution of the vertical plane containing the pedestrian and a portion of the sub- and super-horizontal background. Visibility pedestrians was considered in positive and negative contrast variants, and was then related to the obtained results of the illumination distribution. The analysis of the results of the study indicated the possibility of limited visibility of pedestrians at the crossings despite the satisfactory results obtained from measurements of the illuminance distribution within the crossings.

Study of the ZnO/MoS2 heterostructures-based gas sensor for humidity-independent response

In this study, several strategies including coating with a hydrophobic MoS2 layer, UV light illumination, raising temperature, alternating current (AC), and four-probe measurement have been systematically studied to overcome humidity dependence response behavior for the ZnO sensor. Catalyst-free CVD method was used to prepare pure ZnO nanorods and ZnO/MoS2 heterostructures, and the prototypes were then fabricated on the substrates with Pt interdigital (ID) electrodes, respectively. The gas sensing properties of two sensors were systematically investigated. The ZnO/MoS2 heterostructures-based sensor with four-probe measurement operating at 150 °C shows stable responses during a wide humidity variation range. Furthermore, the ZnO/MoS2 sensor obtains excellent sensing performance to NO2 with a high sensitivity of 12.6 %/ppm and high sensor responses at 150 °C and UV light illumination. Additionally, a low theoretical LoD of 6.5 ppb NO2 is achieved for ZnO/MoS2 heterostructures-based sensor.

3D hierarchical microcubic morphological composite and its application for Bi-functional Humidity/Pressure sensing in TENG architecture

Harnessing the power of contact electrification, triboelectric nanogenerators (TENGs) are a cutting-edge energy technology, where output performance is greatly influenced by the micro/nano scale architectures of triboelectric layers. We present a study on the development of TENG by introducing an advanced 3D hierarchical microcubic morphological structure prepared by simple solution casting method, employing a renewable material, lignin, in combination with eco-friendly polyvinyl alcohol (PVA) matrix. The strategic incorporation of epichlorohydrin (EPCH) as a crosslinker enhances thermal stability, and crosslinking within the lignin/PVA composite (LPC) film. A remarkable outcome of this integration is the emergence of a 3D hierarchical microcubic structure within the LPC film. This structure, with its intricate 3D arrangement, emerges as the cornerstone that underpins the development of LPC-TENGs devices distinguished by their simple fabrication process, elevated output performance, and multifaceted applications. The LPC-TENG, adorned with its unique 3D hierarchical microcubic architecture, establishes new standards in energy harvesting and sensing capabilities with a maximum output power density of 135.4 mWm−2, a short-circuit current of 6.44 μA, and a maximum output voltage of 65 V (5 times higher than PVA-based TENGs). Additionally, the LPC-TENG showed exceptional performance as a self-powered bifunctional sensing system, providing a steady output voltage range of 0–10 V across various humidity levels (20–90 % RH) and a wide usable pressure range (0–162 kPa) with a low detection limit of 1 kPa. We demonstrated the application of the LPC-TENG in energy harvesting from human walking, enabling simultaneous measurements of environmental relative humidity, pressure, and illumination of 27 commercial LEDs. The unique 3D hierarchical microcubic architecture offers an unparalleled foundation for accommodating overall performance and diverse sensing functionalities.

A precise method for the spectral adjustment of LED and multi‐light source solar simulators

AbstractSolar simulators based on light‐emitting diodes (LEDs) usually consist of many spectrally different LEDs, which in sum produce a sun‐like spectrum. On the one hand, this results in the advantage of a high spectral tunability of these systems and on the other hand, however, also in the challenge of a high number of parameters which have to be set for the adjustment of a suitable simulator spectrum. Multijunction solar cells consisting of series‐connected subcells are very sensitive to spectral irradiance conditions, which are affecting the current and the fill factor of the device. A precise adjustment of the simulator spectrum based on the spectral responsivity of the subcells is therefore essential for accurate multijunction measurements. Therefore, the number of spectrally different light sources used should be at least as high as the number of subcells in the device under test. However, for the measurement of multijunction devices, the much higher number of spectrally different light sources in common LED solar simulators results in a plethora of different simulator spectra, potentially suitable for the measurement. Furthermore, the nonlinear intensity characteristics of the utilized LEDs as well as the distance‐dependent illumination uniformity of such solar simulators add complexity when aiming for a precise spectral adjustment. To tackle these challenges, a new spectral adjustment procedure which is based on a least square's solution algorithm and the definition of appropriate boundary conditions for the calculation of suitable simulator settings is introduced in this publication. Focusing on measurements carried out under constant illumination makes the presented method especially applicable for perovskite‐on‐silicon multijunction devices. Therefore, an adapted method for the determination of the solar simulator's spectral properties, considering thermal influences which are particularly relevant when carrying out continuous illumination measurements, is introduced in this work. The presented method is verified applying it on a Wavelabs SINUS 220 LED solar simulator by performing a measurement comparison on a multijunction solar cell with Fraunhofer ISE CalLab's well‐established multilight source solar simulator.

Automation and optimization in daylight analysis and life cycle assessment for automated daylight monitoring device for a metro rail station box in Ahmedabad, India

Daylight analysis and optimization are pre-requisites for energy-efficient and sustainable infrastructure. Conventional practices of designing and providing artificial lighting often ignore the consideration of the availability of natural daylight for the infrastructure. This paper aims to analyze the availability and potential of natural daylight reviewing the sky component type at a designated location, real-time sensor-based illuminance measurement on-site and BIM-based daylight simulation. Consequently, a sensor prototype was deployed to the metro rail station for automated optimization. Firstly, the sky component type of Ahmedabad was determined based on the literature review. Subsequently, sensors were integrated at the strategic grid point location covering the entire metro rail station to collect real-time Illuminance for daylight factor calculation. Furthermore, BIM-based sun path and shadow analysis and daylight simulation were carried out to suggest the possibility and potential of daylight savings. Finally, based on all the analysis and results, a newly designed sensor-based prototype was developed and equipped to enhance automated optimization for daylight savings, which resulted in 29% energy savings monthly. This approach significantly helps the project stakeholders to enhance building energy performance and lead a step closer towards sustainable infrastructure.

The impact of shading by vegetation on the level of daylight in buildings: A case study

An optimal supply of daylight has a positive effect on the physical and psychological health of building users. In the working environment, daylight is a decisive aspect that significantly determines the overall work efficiency of employees. Several factors influence the internal comfort of the environment, but one of the main factors is visual comfort. Nevertheless, excessive sunlight, especially in summer, can cause discomfort. Nowadays, there is a broad spectrum of elimination options for excessive solar gain. This contribution is devoted to a less discussed elimination option, specifically the shading of buildings by surrounding vegetation and its importance in an urbanized environment. The study evaluates the administrative premises of the building for education. The illuminance measurement was performed in two offices with the same orientation. Based on the measured values, the effectiveness of the shading by vegetation element in the current environment and time is detected. The paper aims to investigate the impact of shading by vegetation on the internal visual comfort of employees, based on the concept of daylighting, and recommend appropriate measures to achieve an optimal daylight level.

Using a Mobile Phone as a Measurement Tool for Illuminance in Physics Education

Most primary school students in the Czech Republic have a mobile phone. A mobile phone can measure many physical quantities once the appropriate application has been installed. The terms “Light Meter” or “Lux Meter” are names for applications that measure the physical quantity illuminance. At the time of writing, there are more than 50 such applications available on Google Play. These applications utilise data from the ambient light sensor. The study describes the measurement of illuminance using laboratory equipment and mobile phones with installed applications and further explores the reliability of data collected by mobile phones. A comparison was made between data from applications that were in the default settings and calibrated. The values of different applications installed on the same mobile phone were compared, as well as values of the same application installed on different mobile phones. Values were compared at different distances from the light source and at the same distance, but with varying angles. The reaction time for a mobile phone application to detect changes in illumination was measured. Sensitivity to infrared and ultraviolet radiation was also investigated. Seven general conclusions were drawn from all measurements regarding the use of a mobile phone as a luxmeter instead of professional laboratory equipment, provided that the recommendations are followed.

Analysis and Evaluation of Short City Tunnel Lighting Solutions

The study focused on the lighting in road tunnels within the city of Vilnius. The condition of the lighting was assessed both visually and through measurements of road surface illumination (brightness). High-quality lighting in road tunnels is crucial for ensuring safe and optimal conditions for car travel. Well-designed lighting reduces stress, enhances information visibility for drivers, ensures uniform visibility throughout the tunnel, and promotes efficient energy use. After analysing the data, the required road surface luminance was calculated following the technical regulations applicable to road tunnel lighting design in other countries. The results suggest a need to update the lighting in existing road tunnels by adopting new types of lamps, adjusting their arrangement, and enhancing the physical characteristics of the tunnels.

Analysis and Evaluation of Short City Tunnel Lighting Solutions

The study focused on the lighting in road tunnels within the city of Vilnius. The condition of the lighting was assessed both visually and through measurements of road surface illumination (brightness). High-quality lighting in road tunnels is crucial for ensuring safe and optimal conditions for car travel. Well-designed lighting reduces stress, enhances information visibility for drivers, ensures uniform visibility throughout the tunnel, and promotes efficient energy use. After analysing the data, the required road surface luminance was calculated following the technical regulations applicable to road tunnel lighting design in other countries. The results suggest a need to update the lighting in existing road tunnels by adopting new types of lamps, adjusting their arrangement, and enhancing the physical characteristics of the tunnels.

Ranking-Based Color Constancy With Limited Training Samples.

Computational color constancy is an important component of Image Signal Processors (ISP) for white balancing in many imaging devices. Recently, deep convolutional neural networks (CNN) have been introduced for color constancy. They achieve prominent performance improvements comparing with those statistics or shallow learning-based methods. However, the need for a large number of training samples, a high computational cost and a huge model size make CNN-based methods unsuitable for deployment on low-resource ISPs for real-time applications. In order to overcome these limitations and to achieve comparable performance to CNN-based methods, an efficient method is defined for selecting the optimal simple statistics-based method (SM) for each image. To this end, we propose a novel ranking-based color constancy method (RCC) that formulates the selection of the optimal SM method as a label ranking problem. RCC designs a specific ranking loss function, and uses a low rank constraint to control the model complexity and a grouped sparse constraint for feature selection. Finally, we apply the RCC model to predict the order of the candidate SM methods for a test image, and then estimate its illumination using the predicted optimal SM method (or fusing the results estimated by the top k SM methods). Comprehensive experiment results show that the proposed RCC outperforms nearly all the shallow learning-based methods and achieves comparable performance to (sometimes even better performance than) deep CNN-based methods with only 1/2000 of the model size and training time. RCC also shows good robustness to limited training samples and good generalization crossing cameras. Furthermore, to remove the dependence on the ground truth illumination, we extend RCC to obtain a novel ranking-based method without ground truth illumination (RCC_NO) that learns the ranking model using simple partial binary preference annotations provided by untrained annotators rather than experts. RCC_NO also achieves better performance than the SM methods and most shallow learning-based methods with low costs of sample collection and illumination measurement.

Corneal crosslinking with riboflavin using sunlight.

To assess whether sunlight might be used to induce a biomechanical stiffening effect in riboflavin-soaked corneas similar to the effect observed in corneal crosslinking (CXL) using riboflavin and UV-A light. Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland. Experimental study. 52 porcine eyes were assayed. The concentration of riboflavin in the corneal stroma was estimated using UV-A transmission in a preliminary experiment. Then, the duration of sunlight exposure to achieve a fluence of 7.2/cm 2 was calculated. Finally, de-epithelialized corneas were divided equally into 3 groups and soaked with riboflavin 0.1% (control group and Group 1) or 0.5% (Group 2). Eyes from Groups 1 and 2 were then exposed to sunlight. The elastic modulus was calculated as an indicator of stiffness. Riboflavin concentration in Group B was higher by a factor of 2.8 than Group A. According to live illuminance measurements and stromal riboflavin concentration, the sunlight exposure duration varied between 16 minutes and 45 minutes. Groups 1 and 2 had higher elastic modulus than controls ( P < .0001) but did not differ between them ( P = .194). The stiffening effect was 84% and 55%, respectively. Sunlight exposure of ex vivo corneas soaked in both riboflavin 0.1% and 0.5% resulted in increased corneal stiffness. Specifically, riboflavin 0.1% with longer UV-A exposure showed a trend for a greater stiffening effect, which might open new alleys for the use of oral riboflavin and fractioned sunlight exposure as less invasive CXL techniques.