Illumination Distribution Research Articles

Compact illumination system with variable beam direction and beam divergence

Countless approaches to optimise lighting conditions for indoor and outdoor applications are described in the literature by adaptive dimming schemes or control algorithms. Those methods rely on adapting the emitted flux of individual luminaires in order to adjust lighting conditions to varying circumstances. Complex illumination requirements are tackled by controlling the output of every independent luminaire. In this case, the innovation is rather in software than in hardware, and such approaches are limited by how the LED fixtures can be manipulated. Lighting fixtures with a tuneable radiation pattern are rare, or these fixtures are rather large. This paper introduces a compact lighting system with a collimated light beam of which the beam direction and beam divergence can be adjusted electronically. To realise this optical functionality, a focus tuneable lens and rotatable mirror are combined with two custom-made aplanatic lenses in front of a compact, high-brightness LED. This paper elaborates the optical design of this novel illumination system and discusses the experimental performance of the realised demonstrator. The system functionality is validated by comparing the experimental lighting performance to optical simulations conducted with ray-tracing software. With the proposed system, a fast and flexible adaptation of the generated illumination distribution is possible.

Statistical-Based Control Points Selection for Indoor Illuminance Measurement

The distribution of indoor illuminance affects the health and the performance of humans and is, therefore, subject to audits. Audits are performed after each modification of the light sources, and the currently adopted approach uses a human operator to perform measurements manually. This process is time-consuming, and we, therefore, aim to automate it with a mobile platform. In order to automate the process, we propose an online algorithm for selecting the control points. The algorithm is iterative, and it takes previous measurements into account in order to select the control points adaptively. We show how the proposed method can be combined with a mobile platform to perform the audit autonomously. Initially, the mobile platform, equipped with a laser range finder, is used to build the floor plan of the room. This floor plan is then used to restrict the area within which the control points can be selected. The whole measurement process is then executed without the presence or the intervention of a human operator, and this reduces the time needed for the audit. We have performed simulated and real experiments to demonstrate the performance of the proposed approach.

Optimization method for designing optical elements with an extended light source

A method for designing an optical element with two free-form surfaces generating a prescribed illuminance distribution in the case of an extended light source is considered. The method is based on the representation of the optical element surfaces by bicubic splines and on the subsequent optimization of their parameters using a quasi-Newton method implemented in the Matlab software. To calculate the merit function, a version of the ray tracing method is proposed. Using the proposed method, an optical element with record characteristics was designed: the ratio of the element height to the source size is 1.6; luminous efficiency is 89.1 %; uniformity of the generated distribution (the ratio of the minimum and average illuminance) in a given square region is 0.92.

Impact of Building Orientation on Daylight Availability and Energy Savings Potential in an Academic Classroom

In this paper, daylight availability depending on building orientation in a typical educational classroom was investigated. Measurements of daylight illuminance distributions in the room depth for different illuminance outside the building allowed to determine the conditions when the luminaires in a classroom could be turned off, turned on, or dimmed. The outdoor daylight illuminance on the south-east and north façade of the building was recorded and the numbers of hours per year of university activity during which the lighting had to be switched on (up to 100% or brightened) were determined. Based on these numbers and luminaires powers the electricity consumption for lighting was estimated. It was proven that by using dimming control depending on daylight distribution in a room, comparable energy savings could be achieved for different building orientations. These savings of over 30% were greater than through the implementation of on/off control which, for a south-east oriented classroom reached about 28% and for a north-oriented one they were two times lower. Economic analysis showed payback time for dimming control around two years, which was longer than for on/off control. The electricity consumption estimated experimentally was also compared with the lighting energy numerical indicator (LENI) calculated according the standard EN 15193 1: 2017.

Performance Evaluation of External Light Shelves by Applying a Prism Sheet

To address the increased use of lighting energy in the building sector, research on the use of light shelves has been increasing. Previous studies have focused on applying operating techniques to improve daylighting performance, which reduces the economic efficiency of light shelves and the building energy savings. This study proposes the use of prism sheets to improve the performance of light shelves, a concept which was validated by evaluating the performance related to saving building energy and improving indoor light uniformity through a full-scale testbed. This study used an external light shelf with no prism sheet, a window with a prism sheet applied, and a window with both an external light shelf and prism sheet applied as Case 1, Case 2, and Case 3, respectively, and analyzed the illuminance distribution and lighting energy consumption required to maintain the optimal indoor illumination for each case. This study also derived the optimal specifications for each case to save building energy and considered the flow of natural light to analyze the performance evaluation results. The main findings are as follows: (1) the optimal specifications to improve daylighting performance were derived for Case 1, requiring the application of operating techniques; (2) Case 2 was not suitable for saving energy and improving light uniformity when compared to Case 1; and (3) Case 3 was effective in saving building energy. In Case 3, even when the light shelf was fixed at 20° without moving, it saved building energy and improved light uniformity compared to Case 1. However, the prism sheet in Case 3 should be detached during winter to maximize building energy savings.

Design and fabrication of a freeform mirror generating a uniform illuminance distribution in a rectangular region

The design of a freeform mirror generating a uniform illuminance distribution in a rectangular region with angular dimensions of 30°x15° is presented. The design method is based on the formulation of the problem of calculating the "ray-mapping" as a Monge-Kantorovich mass transportation problem and its subsequent reducing to a linear assignment problem. We describe a mirror fabrication process with the use of milling technology and present results of experimental measurements of the light distribution generated by the mirror. The experimental results are in good agreement with the results of numerical simulations and thus confirm the manufacturability of mirrors designed by the method proposed.

Deep Learning for Optimal Deployment of UAVs With Visible Light Communications

In this paper, the problem of dynamical deployment of unmanned aerial vehicles (UAVs) equipped with visible light communication (VLC) capabilities for optimizing the energy efficiency of UAV-enabled networks is studied. In the studied model, the UAVs can simultaneously provide communications and illumination to service ground users. Since ambient illumination increases the interference over VLC links while reducing the illumination threshold of the UAVs, it is necessary to consider the illumination distribution of the target area for UAV deployment optimization. This problem is formulated as an optimization problem which jointly optimizes UAV deployment, user association, and power efficiency while meeting the illumination and communication requirements of users. To solve this problem, an algorithm that combines the machine learning framework of gated recurrent units (GRUs) with convolutional neural networks (CNNs) is proposed. Using GRUs and CNNs, the UAVs can model the long-term historical illumination distribution and predict the future illumination distribution. Given the prediction of illumination distribution, the original nonconvex optimization problem can be divided into two sub-problems and is then solved using a low-complexity, iterative algorithm. Then, the proposed algorithm enables UAVs to determine the their deployment and user association to minimize the total transmit power. Simulation results using real data from the Earth observations group (EOG) at NOAA/NCEI show that the proposed approach can achieve up to 68.9% reduction in total transmit power compared to a conventional optimal UAV deployment that does not consider the illumination distribution and user association.

Multipopulation genetic algorithm-optimized LED layout in a visible light communication system

Visible light communication (VLC) systems provide illumination and power, and the distributed, specifically made light-emitting diodes (LEDs) are their fundamental sources of light and signal. We propose an arbitrarily distributed LED lamp layout based on a multipopulation genetic algorithm (MPGA) to solve the unevenness of distributions of optical illuminance and power. Twenty LED lamps were taken as an example, and the position coordinates and half-power angles were optimized under the fitness function related to the variance of received power through the coevolution of multipopulations. The simulation results on MATLAB R2016a showed that the distributions of illuminance and power were more uniform, with a variance of power of 0.3978 dBm and a uniformity ratio of illuminance of 87.42%. Moreover, SNR distribution was excellent, with a QSNR of 0.2007. An average root mean square delay spread of 2.22 ns was obtained, with a variance of 5.6250 × 10 − 20. The proposed method is better than the optimization of lamp arrangement, configuration, and genetic algorithm (GA). Furthermore, from iteration curves, the MPGA acts better than the GA in finding the solution. The fitness function value is better than the GA because the latter easily falls into the locally optimal solution. We provide references to design the LED layout and contribute to making a more comfortable communication environment.

Non-uniform sizing of PV cells in the dense-array module to match the non-uniform illumination in dish-type CPV systems

Abstract To reduce the efficiency reduction caused by non-uniformity of illumination, a dense-array module with non-uniform sizing of photovoltaic (PV) cells is proposed for dish-type concentrating PV systems. The non-uniform-sized dense-array module has been designed and analyzed theoretically at the ideal irradiance of Gaussian distribution, which consists of 48 silicone solar cells. Using the ZEMAX optical simulation software, the realistic distribution of the Gaussian-like facula on the PV module has been modelled in a dish-type concentrator system. The experiments are done under the conditions of different alignments to imitate the different two-axis tracking accuracy with or without a homogenizer. Besides, the performances of dense-array modules with the classical uniform-sized and the proposed non-uniform-sized PV cells are analyzed under various illumination distributions using ZEMAX, respectively. Results show that when the deviation angle of tracking is 0, 0.02, 0.2, the photoelectric conversion efficiency and output power of the proposed non-uniform size dense-array module considerably exceeds the traditional uniform size module. Furthermore, when the tracking deviation angle is no more than 0.02°, it is a very definite possibility that the dish-type concentrator system with non-uniform-sized dense-array module need not a homogenizer as a secondary optical element, which may hence simplify the system structure.

Measurements and Simulation Study of Daylight Availability and Its Impact on the Heating, Cooling and Lighting Energy Demand in an Educational Building

This paper deals with the impact of the use of daylight on the overall energy demand for heating, cooling, and lighting in educational buildings. The energy performance of buildings is currently of the utmost importance as current European regulations, starting from 31st December 2020 impose that all new buildings must meet nearly zero-energy building requirements. This paper presents a study of the illuminance distribution in an educational room obtained from measurements and simulation results using two different models. One of the models, integrated with a thermal simulation software, was used to estimate the impact of daylight on the energy demand. The analysis included the use of various window types, lighting control system, reference point location, and daylight calculation model for a sample room in an educational building. Results of the analysis indicate that, due to the high share of lighting demand (reaching up to 78% of the primary energy balance), there is a need to take into account the efficiency of lighting systems during the design process to correctly determine the actual energy balance of a building, increase the quality of the design of lighting systems, as well as to select the optimal parameters of windows.

Principles of Building Systems with Concentrated Solar Energy

Design methods and mathematical models for calculating the characteristics of solar module concentrators with specified optical energy parameters have been developed and investigated. These parameters increase the efficiency of solar power plants operating both in a stationary mode and with a tracking system. Modules with parabolic concentrators, linear and cylindrical photodetectors were used in stationary and solar-tracking arrays. The basic structural and functional parameters of solar modules, the concentration and distribution of concentrated solar radiation over the focal spot width depending on the parametric angle based on the lower and upper parabolas were calculated using physical and mathematical models and derived universal analytical expressions. The given characteristics show possible variants of the dependence of the geometric concentration on the parametric angle of the concentrator for different values of the parameters of the universal analytical equation. The dependences of the geometric concentration on the parametric angle of parabolic concentrators are calculated for different values of the structural parameters: the profile of the module of two conjugate compound concentrators; the concentration distribution along the receiver from the upper and lower concentrators and the module as a whole; and the distribution of illumination along the lateral surface of a cylindrical solar radiation receiver. It is shown that the ratio of the experimental concentrations to the calculated characteristics agrees with the optical efficiency of the modules. The above calculation methods based on the principles of constructing systems with concentrated solar energy allow a comparative analysis of the parameters and the choice of the design of various types of concentrators for the solar modules being developed.

Optimization of Natural Lighting Design for Visual Comfort in Modular Classrooms: Temuco Case

The emergency situations generated by the earthquakes in Chile have revealed the country’s lack of preparation to face these kinds of disasters. Many educational buildings were destroyed by these natural events. In response, a system of modular schools was implemented. Although these have been a temporary fast solution, they have not met the needs that a classroom demands.This article focuses on studying daylighting strategies to achieve the visual comfort of students, as many investigations indicate that this is one of the key environmental factors in their wellbeing and performance. The article also focuses on achieving a correct distribution of horizontal illuminance by implementing design strategies, looking to achieve uniformity inside classrooms, avoiding annoying glare points. The implementation of these strategies fosters the use of daylight in order to reduce the energy consumption of artificial lights and generate optimal conditions for students to perform their school activities.The studied classroom is a modular prototype located in Temuco, Chile, and the evaluated strategies were defined based on the “Guía de Eficiencia Energética para Establecimientos Educacionales (Energy Efficiency Guide for Educational Facilities or GEEEduc)”. These were evaluated independently in order to compare, starting from the results obtained from computer simulations, the compliance of the lighting comfort standards set out in said guide, focusing on the light uniformity and illuminance level indicators. The strategies with the best results were later evaluated in detail, ultimately reaching the case with the best performance.The study proved there are several ways to respond to the presented need, allowing concluding from a set of evaluated strategies, which one of them better serves the required standards. Likewise, implementing strategies of the “GEEEduc” as well as its indicators, results in a practical application of this guideline, allowing the identification of potential errors and good options for future applications.

Evaluation of the Vertical Sky Component without Obstructions for Daylighting in Burgos, Spain

Daylight availability knowledge is the first step for an energetic and visually efficient building and city design. It can be estimated with the Vertical Sky Component (VSC), which is defined as the ratio of the vertical diffuse illuminance over the unobstructed horizontal diffuse illuminance, simultaneously measured at the same point. These illuminance magnitudes are obtained from luxmeter measurements but these data are scarce. Alternatively, VSC can be obtained from prior knowledge of the sky illuminance distribution, which can be measured with a sky scanner device or by reference to the CIE (Commission Internationale de L’Éclairage) Standard classification for homogeneous skies. Both approaches are compared in this study. The coherence of the results obtained for the four cardinal orientations are analyzed by applying classical statistical parameters and luxmeter measurements as references for the results. The measurement campaign was completed between September 2016 and January 2019 in Burgos (Spain), as representative case study and specific contribution of this work. It was observed that the VSC values were higher than 100 in many cases: 21.94% for the south- and 33.6% for the east-facing vertical surfaces. The study highlights the good daylighting conditions in Burgos, mainly due to the predominance of clear skies over much of the year. This fact implies high daylight availability that, with efficient city planning and building design, could potentially lead reduction energy consumption of buildings, improvements in visual comfort, and the well-being of occupants.

Performance analysis on a crystalline silicon photovoltaic cell under non-uniform illumination distribution with a high electrical efficiency

The solar concentrator will cause the non-uniform illumination distribution, which will eventually have a profound impact on photovoltaic (PV) cells. For a crystalline silicon photovoltaic cell, the electrical efficiency with solar concentrator is usually lower than that with uniform illumination distribution. In fact, there is a coupling relationship between the solar concentrating illumination distribution and the PV cell. In this paper, a crystalline silicon photovoltaic cell under non-uniform illumination distribution is indicated, whose electrical efficiency is not negatively affected by the non-uniform illumination distribution. In order to verify that the concentrating PV has a high electrical efficiency, a comparison between the PV under non-uniform and uniform illumination distributions is presented. A series of performance indicators such as the surface voltage distribution, the current density distribution, and the PV conversion efficiency between them are compared. The results show that with the same total illumination intensity, the electrical output of this concentrating PV module with the non-uniform illumination distribution is not reduced, but is 3.4 mW higher than that of the PV cell under the uniform illumination profile, which will provide reference for the design of highly efficient solar concentrating PV.

Small scale optimization in crystalline silicon solar cell on efficiency enhancement of low-concentrating photovoltaic cell

Compared with conventional silicon solar cell, concentrating photovoltaic cell has a higher incident illumination intensity and non-uniform illumination intensity distribution. There is a close relationship between the illumination intensity and the resistance and shading losses of front metal fingers. In this paper, according to the non-uniformity of the illumination distribution formed by the concentrator, the effects of different finger numbers and spacing on the performance of low-concentrating photovoltaic cells were studied. First, low-concentrating photovoltaic cell modules with different finger numbers and spacing were established, and efficiency of these modules was compared to determine the optimal finger numbers and spacing of the front metal fingers. Then, effects of the shading losses, finger resistance and lateral spreading resistance on the performance of the low-concentrating photovoltaic cell were analyzed. Results show that for the specific illumination intensity distribution of the low-concentrating photovoltaic cell when the numbers and spacing of the front metal fingers are optimized, efficiency of the low-concentrating photovoltaic cell can be increased from 13.805% to 13.837%. Additionally, it can be concluded that the optimization of the number and spacing of the front metal fingers in the crystalline silicon solar cell is an efficient way to improve the electrical performance of the concentrating photovoltaic cell.

An Alternative Approach for High Uniformity Distribution of Indoor Lighting LED

A high accurately theoretical analysis for high uniformity illumination distribution on the ceiling of indoor lighting LED system based on the super-positions is proposed and performed. Starting from the non-uniform illumination distribution of two LED sources, the dependences of the uniformity ratio on the height of the LED source and the length of the ceiling are investigated. The low intensity in the region near the side-wall can be avoided by rotating the LED source with a small angle, but the low uniformity illumination distribution at the center of the ceiling still exists. The aim of this work proposes the alternative design and approach for several configurations and demonstrates that can be obtained high uniform illumination distribution. The redistributed factor of the illumination through the lens is also considered and calculated. The investigation of this work will be a general guideline for designing the high uniform LED indoor lighting systems as well as being valuable materials for the LED lighting manufacturing industry.

Efficiency on artificial lighting energy: dome, pyramid and flat shaped - ceiling mosque

Indonesia is the largest Muslim country in the world, around 87.2% of its population are Muslim. Mosque, as the center of Muslim activities, has important roles for Muslim’s physical and social aspects. Therefore, it causes a massive addition of mosque buildings in Indonesia. Mosques are mostly built in spacious areas that increase the possibility of extravagance in lighting. This study explores the different types and configuration patterns of artificial lighting to be applied in the different shapes of mosque ceiling and how they relate to energy efficiency. Using the software simulation DIALux, this study aimed to find the best artificial lighting types and configuration patterns that possible for most efficient energy in terms of its illuminance distribution quality. Al Musyawarah Mosque, al Falah Mosque and Sunda Kelapa Mosque in Jakarta are the sample chosen for this study. Those mosques were chosen because their ceiling shapes represent the shape of Indonesian mosque ceiling in general: dome, pyramid and flat-shaped ceiling. As the result, a basic guideline for efficient lighting configuration in different shaped ceiling mosques is proposed.

Research Note: Describing average illuminance for P-class roads

Design criteria for lighting in subsidiary roads usually include a minimum average horizontal illuminance, widely assumed to be the arithmetic mean illuminance. Analyses of the illuminance distributions over thirty road sections shows that the distributions are not normal and hence the median is more appropriate than the arithmetic mean as a measure of central tendency: the medians are significantly lower than the arithmetic means but the two are highly correlated. Design recommendations should state whether it is the arithmetic mean or median and not just the ‘average’ that is required.

Detection method of manufacturing defects on aircraft surface based on fringe projection

For high-value aircraft, in order to ensure their stealth, pneumatic and safety characteristics, surface geometric defects such as unacceptable rivet height and seam width must be accurately detected during the manufacturing process. These defects need to be controlled within a very small scope of error. Traditional defect detection methods are difficult to meet the actual requirements of manufacturing of advanced aircrafts in terms of information dimension, detection accuracy and efficiency. In this paper, a new method of high-precision 3D defect detection for controlling riveting and seam quality is proposed. For the complexity of illumination distribution on aircraft surface, first, an accurate surface measurement method based on fringe projection is proposed. Then, based on two-dimensional and three-dimensional information, a method of automatic identification and location of rivets and seams is developed. Finally, a visualization method based on augmented reality is proposed to help improve the operator's work efficiency. The experimental results show that the method has high detection accuracy and practicability.

Development and validation of a photobioreactor for uniform distribution of light intensity along the optical path based on numerical simulation

A theoretical approach was followed to optimize the design of a cylindrical photobioreactor for wastewater treatment based on algal culture. In particular, the problem of uneven light distribution that impairs algal growth was minimized by optimizing the area of uniform illumination distribution for a bioreactor design that can be enlarged without affecting its performance. The theoretical analysis was based on modeled simulations to determine the best configuration and illumination mode. The Monte Carlo method was used to simulate the illumination distribution inside the bioreactor, and the relationships between the width of the area with uniform illumination and related parameters were explored. Based on these theoretical considerations and predictions, an actual experimental photobioreactor was built containing a working area (where culture of Chlorella pyrenoidosa was enabled) and a catchment area for effluent. The performance of this bioreactor was tested with synthetic wastewater as a substrate. The light distribution was found to be relatively uniform inside the bioreactor, supporting excellent algal growth and resulting in maximum removal rates of 84.41% for total nitrogen, 99.73% for total phosphorus, 85.03% for NH4+-N, and 75.94% for chemical oxygen demand (COD) over a period of 32days of operation. The presented approach provides new insights for improving the efficiency and scalability of photobioreactors and promotes their development for wastewater treatment and resource utilization.