Uniform Illumination Distribution Research Articles

Segmentation of THz holograms for homogenous illumination

This paper investigates the feasibility of applying the hologram segmentation method for homogeneous illumination. Research focuses on improving the uniformity of the illumination obtained from diffractive optical elements in the THz range. The structures are designed with a modified Ping-Pong algorithm and a neural network-based solution. This method allows for the improvement of uniform illumination distribution with the desired shape. Additionally, the phase modulations of the structures are divided into segments, each responsible for imaging at different distances. Various segment combination methods are investigated, differing in shapes, image plane distances, and illumination types. The obtained image intensity maps allow for the identification of the performance of each combination method. Each of the presented structures shows significant improvements in the uniformity of imaged targets compared to the reference Ping-Pong structure. The presented structures were designed for a narrow band case—260 GHz frequency, which corresponds to 1.15 mm wavelength. The application of diffractive structures for homogenization of illumination shows promise. The created structures perform designed beamforming task with variability of intensity improved up to 23% (standard deviation) or 45% (interquartile range) compared with reference structure.

Method for evaluation of the optical uniformity distribution in the white LEDs-based visible light communication applications

The uniformity characteristic of emitted radiation in VLC applications is a factor that can affect the efficiency of a detector and the overall efficiency of the VLC system. In this paper, we theoretically investigate the optical uniformity characteristic of using LEDs in VLC applications in terms of the parameter of the emission angle of LEDs and the spatial distribution of LEDs. The result indicates that the optical uniformity can be controlled at a high level by controlling the emission angle of the LED or distributing the LEDs in the room's space. Full Text: PDF References E.-F. Schubert, J.-K. Kim, "Solid-State Light Sources Getting Smart", Science 308, 1274 (2005). CrossRef N. Narendran, Y. Gu, "Life of LED-based white light sources", J. Display Technol. 1, 167 (2005). CrossRef E. Schubert, Light-Emitting Diodes (Cambridge, Cambridge Univ. Press 2006). CrossRef C.C. Sun, Q.K. Nguyen, T.X. Lee, S.K. Lin, C.S. Wu, T.H. Yang, Y.W. Yu, "Active thermal-fuse for stopping blue light leakage of white light-emitting diodes driven by constant current", Sci. Reports 12, 12433 (2022). CrossRef Z. Ghassemlooy, W. Popoola, S. Rajbhandari. Optical Wireless Communications System and Channel Modelling with MATLAB (Florida, CRC Press, Taylor & Francis Group, 2013). CrossRef A. Burton, H. Le Minh, Z. Ghasemlooy, S. Rajbhandari, "A study of LED lumination uniformity with mobility for visible light communications", IEEE 2012 Int. Workshop on Opt. Wireless Comm. (IWOW), Pisa, Italy, 2012. CrossRef M.S.M. Gismalla, M.F.L. Abdullah, M.I. Niass, B. Das, W.A. Mabrouk. "Effect of optical attocells deployment on the RMSD spread in indoor visible light communication systems", Int. J. Commun Syst. e4349 (2020). CrossRef C. Wang, J. Wang, J. Zhang, J. Wang, H. Du, J. Wang, "Research on uniform illumination distribution of indoor visible light communication", Proc. SPIE 12062, AOPC 2021: Optoelectronics and Nanophotonics (2021). CrossRef M.V. Bhalerao, M. Sumathi, S.S. Sonavane. "Line of sight model for visible light communication using Lambertian radiation pattern of LED", Int. J. Comm. Systems (2016). CrossRef J.F. Zang, Y. Piao. "Research on visible light communication system based on white LEDs", Proc. SPIE 10255, (2016). CrossRef M. Oliveira, F.C.B. Tosta, D.E.F. Guillen, P.P. Monteiro, A.A.P. Poh, "Theoretical and Experimental Analysis of LED Lamp for Visible Light Communications", Wireless Personal Communications 125, 3461(2022). CrossRef J.P. Ding, C. Lin, J.T. Wang, H. Yang, "Effects of Optical Beams on MIMO Visible Light Communication Channel Characteristics", Sensors 22, 216 (2022). CrossRef X. Zhang , N. Zhao, F. Al-Turjman, M.B. Khan, X. Yang. "An Optimization of the Signal-to-Noise Ratio Distribution of an Indoor Visible Light Communication System Based on the Conventional Layout Model", Sustainability 12, 9006 (2020). CrossRef A. Kaewpukdee, P. Uthansakul, "Characteristic of Line-of-Sight in Infrastructure-to-Vehicle Visible Light Communication Using MIMO Technique", Materials Continua 74, 1026 (2023). CrossRef

FS-GAN: Fuzzy Self-guided structure retention generative adversarial network for medical image enhancement

Improving the quality of medical images is helpful for doctors to perform clinical diagnosis and treatment. Many medical image enhancement methods can achieve good performance when training on paired data. However, acquiring paired high/low-quality medical images for training image enhancement models is challenging, and these methods are not applicable to unpaired images while also lacking structural information preservation. To address these problems, this paper proposes a fuzzy self-guided structure retention generative adversarial network (FS-GAN), which can perform unpaired learning. Specifically, we develop a fuzzy discriminator to distinguish real images from generated images in the fuzzy domain, which is able to improve the enhanced performance of the model. Moreover, we design the self-guided structure retention module (SSRM) and illumination distribution correction module (IDCM) to capture the structure information of nerve fibers in a self-guided manner and correct the illumination distribution of the image to improve the visual effect. Compared with the existing methods, the experimental results show that the enhanced images generated by the FS-GAN exhibit the most complete texture structure and uniform illumination distribution, and FS-GAN performs well in downstream application tasks.

Design of optical elements for an extended light source

Using the previously developed optimization method for an extended light source [Byzov EV, Kravchenko SV, Moiseev MA, Bezus EA, Doskolovich LL. Optimization method for designing double-surface refractive optical elements for an extended light source. Opt Express 2020; 28(17): 24431-24443. DOI: 10.1364/OE.400609], we designed a compact refractive optical element (the ratio of the element height to the light source size being 1.55) providing a uniform illuminance distribution in a shifted rectangular region. An application of the optimization method for calculating the so-called TIR-elements, exploiting the phenomenon of the total internal reflection of rays, is considered. For an extended light source, compact TIR-elements with freeform exit surfaces that generate uniform illuminance distributions in a rectangular region are designed. The results of the work show promise for a wide class of problems of designing compact optical elements for light-emitting diodes.

Optimization Process Applied in the Thermal and Luminous Design of High Power LED Luminaires

This work proposes the design of an optimization method for high-power LED luminaires with the introduction of new evaluation metrics. A luminaire geometry computational method is deployed to conduct thermal and optical analysis. This current effort novels by designing a tool that enables the analysis of uniformity for individual luminaire over the target plane in accordance with international regulatory standards. Additionally, adequate thermal management is conducted to guarantee nominal operation standard values determined by LED vendors. The results of this optimization method present luminaire models with different geometries that allow the stabilization of the temperature within the safety and uniform illuminance distribution thresholds. The resulting solution proposes the design of a 2×2 HP-LED rectangular luminaire. During simulations, the temperature of the LED reaches a maximum value of 73.9∘ C in a steady state with a uniform index of 0.228 for its individual luminaire. The overall uniform index identified for two separate and adjacent luminaire points in a pedestrian walk is 0.5413 with a minimal illuminance of 36.95 lx, maximum illuminance of 93.65 lx and average illuminance of 68.27 lx. Overall, we conclude that the currently adopted metric, which takes into consideration only the ratio between the minimum and the average illuminance, is not efficient and it cannot distinguish different luminaire geometry standards according to their uniform illuminance distribution. The metric proposed and designed in this work is capable of evaluating illuminance and thermal threshold criteria, as well as classifying different sorts of luminaries.

Numerical Analysis of the Performance of an Innovative Daylighting System Named Modified Double Light Pipe

This paper focuses on the performance of an innovative daylighting system named Modified Double Light Pipe (MDLP). It consists of a device integrating a Double Light Pipe (DLP) with a light shelf. The DLP has been created by the authors to enter daylight into two levels underground buildings. It involves an excessive bulk and the risk of glare in the passage environment. The MDLP is an attempt to solve these problems by coupling the DLP and the light shelf technologies. The authors used a numerical approach modeling the MDLP by the software Rhinoceros and simulating its performance by Grasshopper plugins Ladybug and Honeybee. After calibrating the software by the comparison between numerical and experimental data on the DLP, they carried out a numerical analysis on the MDLP in steady-state and dynamic conditions. In steady-state regime, the MDLP performs better than the DLP, giving quite a uniform illuminance distribution on the horizontal work plane. This is confirmed by the results of the dynamic analysis, carried out evaluating the metric Spatial Daylight Autonomy (sDA). Moreover, the risk of glare is avoided by the MDLP, thanks to the presence of the light shelf that prevents the observer from seeing the device directly.

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.

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.

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.

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.

Fiber-based daylighting system using trough collector for uniform illumination

A lot of research attention has been given to collect sunlight through solar concentrators for indoor illumination. Traditional, parabolic trough as a line focus with single array of fibers had mechanical design and installation issues. Here, a novel daylighting system is proposed to transmit maximum light into the optical fibers using parabolic trough as the primary collector and nonimaging reflector as the secondary reflector. The proposed system increases light levels, improves installations difficulties, and maintains long-term reliability. All modules are designed and verified through raytracing simulation for calculating the efficiency and achieving the required light-levels. The proposed trough-based design inserts maximum light into the fiber bundle, which is placed at the center of the trough. Further, the fiber-coupled bi-layer prismatic optical diffuser provides relatively high uniform illuminance distribution. Simulation results have shown that the light concentration of 285, an optical efficiency of 42%, and an acceptance angle of ±1.1° are achieved that are better than that of previous trough-based daylighting system.

Design Ultra-Compact Aspherical Lenses for Extended Sources Using Particle Swarm Optical Optimization Algorithm

This paper presents a global optimization algorithm specifically tailored for ultra-compact aspherical lens design problems for extended LED sources. The main purpose is to obtain prescribed illumination patterns, particularly the uniform illuminance distribution. This method begins by calculating the initial aspherical lens with two surfaces based on point source approximation. Then a system of polynomials is employed to fit the meridian curves of the two surfaces. In the optimization process, we use the particle swarm optimization (PSO) algorithm to automatically find the optimal polynomial coefficients when the ray tracing simulation is being performed. A series of ultra-compact aspherical lenses with dimension ratio of h / d ranging from 0.95 to 1.25 are presented, where h denotes the center height of the lens and d represents the diameter of the extended source. The results show the high efficiency and versatility of the proposed method in prescribed illumination design for extended LED sources in three-dimensional rotational symmetry geometry. Additionally, an aspherical lens is fabricated and tested, and its practical performance approaches the design.

Design of axisymmetric double-surface refractive optical elements generating required illuminance distributions

We propose a novel technique for designing double-surface axisymmetric refractive optical elements with minimized Fresnel losses and maximized lighting efficiency. The design of the optical element is reduced to the integration of three explicit ordinary differential equations. Minimization of the Fresnel losses is provided by ensuring equal refraction angles on both “working” surfaces of the optical element. To demonstrate high performance of the method, we designed axisymmetric double-surface optical elements generating uniform illuminance distributions both in the far (angular size of 50°) and in the near (angular size of 90°) field. The lighting efficiency exceeds 87.8% for both point and extended light sources. Besides, we demonstrated that optical surfaces designed using the proposed method can serve as an excellent initial approximation in the case of a large extended light source. In the considered example with the ratio of the element height to the source diameter of only 2.2, the lighting efficiency of the optimized element exceeds 89.5%, whereas the uniformity of the resulting illuminance distribution exceeds 96%.

Design of an optical attocells configuration for an indoor visible light communications system

Visible light communications (VLC) is deemed as a promising technology for future indoor cellular communications due to its unique features, namely unlicensed free spectrum, high bandwidth, high security, and low power consumption. A small base stations (BS) called optical attocells are mounted on the ceiling of the room to provide communication and illumination simultaneously. In this paper, an optical attocells configuration model is proposed with the aim of providing a uniform illumination distribution while the field of view (FOV) is optimized to increase the receiver gain, furthermore, improving the received power and SNR distribution. The average illumination level of 635.6113 Lx is obtained, besides that, the minimum received power is improved from −2.17 to −1.286 dBm as compared with the previous studies. The proposed optical attocells model has used small number of LEDs chips, and hence, a reduction in link power consumption by 30.6% is achieved. Also, it was resolved the blind area at the centre of the room, and the total received power at the centre is improved from 3.2 to 5.967 dBm.

Fast design method of smooth freeform lens with an arbitrary aperture for collimated beam shaping.

A method is presented for the fast design of a smooth freeform lens to tailor a collimated light beam with an arbitrary contour. This method begins by calculating an initial surface based on a simplified ray mapping. Then the surface is fitted by a system of Zernike polynomials, whose weights are treated as the optimization variables for further optimization. In the optimization, the objective function is analytically calculated using a partial differential-equation-based approach. To validate the effectiveness of the proposed method, a freeform lens is designed for a collimated Gaussian beam with a spline contour to form a uniform illumination distribution with another spline contour, which takes only 26 s. A freeform lens is also fabricated and experimented, and its practical performance approaches the design.

用于机器视觉测量曲面照明的LED阵列优化算法设计

用于机器视觉测量曲面照明的LED阵列优化算法设计

Design of Extruded refractive optical elements to generate a prescribed intensity distribution

A new method for the design of extruded optical elements with two refractive surfaces is presented. The method is based on the developed fast ray-tracing procedure, in which optical surfaces are approximated by a set of planes. High efficiency of the proposed method is illustrated by the examples of designed extruded optical elements for generating uniform intensity and illuminance distributions. The luminous efficacy of the optical element is shown to be over 89 %, whereas the relative root-mean-square error of the generated irradiance distribution is under 2 %.

Design of high-compactness freeform optical surfaces via energy accumulating optimization.

Energy accumulating optimization based on dynamic programming is proposed to design non-rotational 3D high-compactness freeform optical surface for extended source. Each small piece which constructs the freeform optical surface is treated as a stage, and the normal vectors of the small pieces are treated as the decision variables. Then each small piece with a normal-vector-selection-range is calculated stage-by-stage, which is different to the common used loop-iterations-optimization-strategy. The state of the accumulated light distribution on the target plane is varied with the evolvement of the calculations. The optimal decisions are ascertained in a retrospective way only after all the calculations are finished, which are ensured by the principle of optimality. Moreover, several treatments are proposed to confine the normal vector selection range, and the feedback adjustment is developed as well. The effectiveness of this method is demonstrated by designing the 20 mm height freeform optical surfaces for 10 mm diameter Lambertian sources to achieve uniform illuminance distributions with dual-axial symmetry and single-axial symmetry, respectively. The energy utilization ratios are above 82% with Fresnel loss, while the relative standard deviation of the illuminance distribution can be less than 0.2.

Design methodology for micro-discrete planar optics with minimum illumination loss for an extended source.

Recently, studies have examined techniques for modeling the light distribution of light-emitting diodes (LEDs) for various applications owing to their low power consumption, longevity, and light weight. The energy mapping technique, a design method that matches the energy distributions of an LED light source and target area, has been the focus of active research because of its design efficiency and accuracy. However, these studies have not considered the effects of the emitting area of the LED source. Therefore, there are limitations to the design accuracy for small, high-power applications with a short distance between the light source and optical system. A design method for compensating for the light distribution of an extended source after the initial optics design based on a point source was proposed to overcome such limits, but its time-consuming process and limited design accuracy with multiple iterations raised the need for a new design method that considers an extended source in the initial design stage. This study proposed a method for designing discrete planar optics that controls the light distribution and minimizes the optical loss with an extended source and verified the proposed method experimentally. First, the extended source was modeled theoretically, and a design method for discrete planar optics with the optimum groove angle through energy mapping was proposed. To verify the design method, design for the discrete planar optics was achieved for applications in illumination for LED flash. In addition, discrete planar optics for LED illuminance were designed and fabricated to create a uniform illuminance distribution. Optical characterization of these structures showed that the design was optimal; i.e., we plotted the optical losses as a function of the groove angle, and found a clear minimum. Simulations and measurements showed that an efficient optical design was achieved for an extended source.

Energy and user acceptability benefits of improved illuminance uniformity in parking lot illumination

This study set out to understand the benefits of improved illuminance uniformity in parking lots in terms of user perception and acceptability, as well as energy use, and to demonstrate that light-emitting diodes (LEDs) can achieve uniform distributions more efficiently than traditional light sources. The results from a field evaluation showed that more uniform illuminance distributions are favourably perceived by people in terms of goodness of illumination, ability to see around and at a distance, and perception of safety – all of this at a much lower average horizontal illuminance. Thus, improving uniformity alone can translate into lower energy use and potential for less glare and light pollution. Optical modelling showed that LEDs have a much greater potential to efficiently produce uniform illuminance distributions than larger light sources such as high pressure sodium or metal halide.