Anti-fungal blue light (ABL) therapies have been widely studied to treat various microbial infections in the literature. The blue light with wavelengths ranging from 400 to 470 nm has been reported to be effective to inhibit various kinds of bacteria and fungi. The existing studies usually report the viability rates of the pathogens under the irradiation of the blue light with different dosage parameters. However, to the best of our knowledge, there is still no work especially focusing on studying the effect of ABL therapies on treating candida vaginitis, where it is important to study the viability of both the Candida albicans (C. albicans) and the human vaginal epithelial cells. It is the purpose of this work to conduct ABL experiments on both of these two cells, analyze the effects, and determine the best ABL wavelength out of three candidates, i.e., 405-nm, 415-nm, and 450-nm wavelength. The viability rates of the C. albicans and the human vaginal epithelial cells irradiated by the three blue LED light sources were measured, whose irradiance (power density) were all set to 50 mW/cm². The dynamic viability models of the C. albicans and the epithelial cells were built based on the experimental data. Moreover, in this work, we also built a functional relationship between the viability of these two types of cells, by which we further compared the effects of the blue light irradiation on both the C. albicans and vaginal epithelial cells. The experimental data showed that when an approximately 80% inhibiting rate of the C. albicans was achieved, the survival rates of the epithelial cells were 0.6700, 0.7748, and 0.6027, respectively for the treatment by the 405-nm, 415-nm, and 450-nm wavelength light. On the other hand, by simulating the functional relationship between the viability of the two types of cells, the survival rates of the epithelial cells became 0.5783, 0.6898, and 0.1918 respectively using the 405-nm, 415-nm and 450-nm wavelength light, when the C. albicans was completely inhibited. Therefore, both the experimental data and the model simulation results have demonstrated that the 415-nm light has a more effective anti-fungal result with less damage to the epithelial cells than the 405-nm and 450-nm light.

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Microbial infection is one of the most common diseases in the world, which gives rise to morbidity and mortality. At present, the main treatment is using antibiotic drugs. However, the side effects range from fever and nausea to major allergic reactions cannot be ignored. Moreover, the increasing drug resistance also necessitates a new safe alternative therapeutic approach against the microbial infections. As non-antibiotic methods, photodynamic therapies (PDT) and anti-microbial blue light (ABL) therapies have been investigated in this field. However, one challenge of the PDT is the introduction of photosensitizers to the specific pathogens rather than the host cells. In contrast, ABL therapies inactivate the microbes without the involvement of exogenous photosensitizers. The general mechanism of ABL therapies is that ABL can excite the endogenous photosensitizers, and trigger the accumulation of cytotoxic reactive oxygen species (ROS), which in turn leads to cell damage. In this study, we investigated the inhibitive capability of the 405nm LED light source on Candida albicans (C. albicans). C. albicans is the most common pathogen of fungal infections. The intracellular ROS level of C. albicans was detected after the ABL irradiation. The results obtained from this study demonstrated that irradiation of 405nm LED significantly inactivated the C. albicans. The viability of C. albicans was reduced to 1% after 25 minutes of ABL exposure of 50mW/cm². On the other hand, the intracellular ROS was increased by the ABL irradiation. This study demonstrates the effectiveness of applying 405nm LED to threat the infection caused by C. albicans, as the result of the stimulated accumulation of the intracellular cytotoxic ROS by this light.

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Vertical space bears great potential of solar energy especially for congested urban areas, where photovoltaic (PV) windows in high-rise buildings can contribute to both power generation and daylight harvest. Previous studies on sun-tracking PV windows strayed into the trade-off between tracking performance and mutual shading, failing to achieve the maximum energy generation. Here we first build integrated models which couple the performance of sun-tracking PV windows to the rotation angles. Secondly, one-degree-of-freedom (DOF) and two-DOF sun tracking are mathematically proven to be not able to gain either maximum power generation or non-glare daylighting under reasonable assumptions. Then we derive the optimum rotation angles of the variable-pivot-three-degree-of-freedom (VP-3-DOF) sun-tracking elements and demonstrate that the optimum VP-3-DOF sun tracking can achieve the aforementioned goals. When the restriction of the proposed model is relaxed, the same performance can be achieved by the optimum one-DOF sun tracking with extended PV slats and particular design of cell layout, requiring less complicated mechanical structures. Simulation results of nine global cities show that the annual energy generation and average module efficiency are improved respectively by 27.40% and 19.17% via the optimum VP-3-DOF sun tracking over the conventional perpendicular sun tracking. The proposed optimum sun-tracking methods also reveal better protection against sun glare. The optimum VP-3-DOF sun tracking is also demonstrated to be applicable to horizontal PV windows, as those applied in the sun roof of a glass greenhouse.@en

In lighting systems consisting light-emitting diodes (LEDs), excessive temperature is a main cause of degraded luminous efficacy, which leads to reduced average illuminance and distorted illumination rendering. Modeling the thermal dynamics of LEDs is hence essential in designing thermal dissipators and controllers for maintaining constant illuminance or chromaticity. In the existing literature, both physical modeling and system identification have been proposed, which all find the dependence of the temperature on the input power. When the power fluctuates, e.g., due to dimming control, the thermal dynamics becomes nonlinear. Moreover, when a photoelectrothermal model is used in the control synthesis, the nonlinearity due to the product of the temperature-dependent efficacy and the input power must be considered. These nonlinearities are either ignored or linearized in most existing methods. The main contribution of this work is treating the aforementioned nonlinearities in a linear parameter varying (LPV) framework. First, the nonlinear thermal dynamics is identified by LPV system identification techniques. Then, a controller to track reference illuminance is designed by H_∞ control techniques to be robust to both the temperature and the disturbance from ambient light. The identification data and the designed controller are collected from and verified on a real experimental setup.

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Enhancing the color saturation of objects via illumination with specially designed light spectra is promising in many commercial and scientific applications. Existing literature has focused on studying the colors that can be rendered by white light with various correlated color temperatures, and by the mixed light from various monochromatic light-emitting diodes. However, very little literature has been devoted to methods that can actively configure the light spectrum to enhance the color saturation of an arbitrary object. This paper proposes an optimization-based method to extend the gamut that can be achieved by a given polychromatic lamp toward a chosen direction, i.e., to increase the saturation of a specific color. Moreover, to trade-off the increased saturation of a color sample with the reduced colorfulness of other samples, constraints with tunable thresholds are imposed to the optimization problem to bound the variation of a contrast color sample. In addition, the effect of uncontrollable ambient light can be taken into account by mild modifications of the optimization problem. Simulation results show that the optimized light spectrum can effectively enhance the saturation of any specific color, while maintaining the other rendered colors as intact as possible. Visual experiments have also been conducted with 22 human subjects, whose responses agree with the simulation results.@en

Diverse solar irradiance spectra can be observed under different conditions of time, date, location, weather, etc. Since the solar irradiance spectrum is required by certain scientific and engineering applications, obtaining accurate spectral data is essential. Measurements by spectrophotometers are able to achieve accurate real-time data with high resolution, but at high expense. While in some engineering applications, the requirements on accuracy and resolution are much lower than that in a typical scientific research. Therefore, a rapid method of estimating the solar spectrum is proposed based on an available spectral model in this paper. In order to achieve fast estimation, we simplify the input parameters of this model into five key inputs, including latitude and longitude, altitude, date and time, sky and ground type. The first three parameters are easy to obtain from GPS and the internet. Sky and ground types include common types of sky and ground, which can be input manually or processed automatically by analyzing a digital image of target sky or ground. The automatic input is realized through dominant color extraction or by training an artificial neural network. Results show that the proposed rapid method can generate different spectral power distributions based on distinct input conditions. Two device frameworks are also proposed to implement the rapid method, which is applicable to many fields. LED lighting is one of the most prominent applications. Users can easily share local sunlight with each other through an APP in mobile phones@en

This chapter describes a system-level design method of automatically diagnosing and compensating LED degradations in large LED systems, also known as solid-state lighting (SSL) systems. A failed LED may significantly reduce the overall illumination level, and destroy the uniform illumination distribution achieved by a nominal system. The main challenge in diagnosing LED degradations lies in the usually unsatisfactory observability in a large LED system, because the LED light output is usually not individually measured. In this chapter, we review a solution which we have recently developed in ref. (Dong et al. Optics Express 19:5772-5784, 2011). This solution tackles the observability problem by assigning pulse width modulated (PWM) drive currents with unique fundamental frequencies to all the individual LEDs. Signal processing methods are applied therein to estimate the individual illumination flux of each LED. Statistical tests are described to diagnose the degradation of LEDs. Duty cycle of the drive current signal to each LED is reoptimized once a fault is detected, in order to compensate the destruction of the uniform illumination pattern by the failed LED. The combined diagnosis and control reconfiguration is known as fault tolerant control (FTC) in control theory literature. In this chapter, we first review the essential technical details of the solution in ref. (Dong et al. Optics Express 19:5772-5784, 2011), and then focus on detailed simulation case studies, which clearly verify the effectiveness of this FTC solution for multiple LED degradations at the same time.@en

This paper describes a new design concept of automatically diagnosing and compensating LED degradations in distributed solid state lighting (SSL) systems. A failed LED may significantly reduce the overall illumination level, and destroy the uniform illumination distribution achieved by a nominal system. To our knowledge, an automatic scheme to compensate LED degradations has not yet been seen in the literature, which requires a diagnostic step followed by control reconfigurations. The main challenge in diagnosing LED degradations lies in the usually unsatisfactory observability in a distributed SSL system, because the LED light output is usually not individually measured. In this work, we tackle this difficulty by using pulse width modulated (PWM) drive currents with a unique fundamental frequency assigned to each LED. Signal processing methods are applied in estimating the individual illumination flux of each LED. Statistical tests are developed to diagnose the degradation of LEDs. Duty cycle of the drive current signal to each LED is re-optimized once a fault is detected, in order to compensate the destruction of the uniform illumination pattern by the failed LED.@en