Dimming Levels Research Articles

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.

Direct Illuminance-Contribution-Based Lighting Control for IoT-Based Lighting Systems in Smart Buildings

With the advent of low-voltage light-emitting diodes (LEDs) and advances in Internet of Things (IoT) technologies, smart buildings have recently become more energy efficient. Nevertheless, the lighting-control system is one of the major sources of electrical energy consumption in commercial buildings. This study proposes a direct illuminance-contribution-based lighting-control framework to reduce the energy of LED luminaires and ensure illuminance for user requirements in smart buildings. Specifically, we designed a direct illuminance-contribution-based lighting-control algorithm (DIC-LCA) using luminaires that are ideally axisymmetric with all light emitted below the horizontal plane and developed a WiFi lighting controller for the IoT-based lighting-control systems in smart buildings. The DIC-LCA can adjust the dimming level by calculating the illuminance based on the line of sight (LOS) distance for energy saving and user satisfaction. After simulation analysis, we prove that energy savings can be achieved by controlling the dimming levels of LED luminaires with high light contribution.

A multi-objective optimization method for enclosed-space lighting design based on MOPSO

With the rapid development of underground spaces and manned cabins, the design of enclose-space has received attention. Humans working in enclosed-space for a long period of time are prone to fatigue, which in serious cases can lead to human errors and major accidents. Therefore, the optimized design of enclosed-space is of great research significance to enhance the efficiency and comfort of workers. The lighting environment is one of the important objectives of the optimized design of enclosed-space, and the current research on lighting design often focuses on single-objective reduction of energy consumption or improvement of visual effects, and lacks attention to non-visual effects. We propose multi-objective optimal control strategy for enclosed-space lighting systems, taking the visual effects, non-visual effects, and energy efficiency of lighting as the optimization objectives and constraints, combined with multi-objective particle swarm optimization algorithm. Firstly, we obtain a set of optimal Pareto front solution for the dimming level by improving the algorithm. Secondly, to select appropriate lighting strategies according to different working scenarios, we introduce the fuzzy integrated evaluation method of experts to find the best compromise. Finally, we used a manned simulated enclosed cabin based on DIALux evo for a case study to compare the optimization results with baseline solutions. The results show that when we employed the improved dimming strategy, the energy efficiency and visual comfort were significantly improved compared with the baseline lighting design. The proposed method can satisfy human non-visual effects requirements, providing a research reference for future enclosed-space lighting optimization.

Unipolar GFDM With Dimming Support for Visible Light Communications

We propose and analyze a unipolar generalized frequency division multiplexing (GFDM) modulation scheme with dimming support for visible light communications (VLC). In the proposed method, the dimming level can be controlled at a transmitter using a single parameter that a receiver need not know. In addition, the dimming parameter can be adjusted by the transmitter at any time without affecting the quality of data transmissions. Expressions of the illumination percentage and the bit error rate (BER) are derived taking into account the dimming parameter, and validated through comparisons with simulation results. Using these expressions, it is possible to specify the dimming parameter at the transmitter based on the desired illumination percentage and estimate the corresponding BER for data transmissions. Numerical results indicate that, compared to adjusting the direct current (DC) bias for dimming control, the proposed method provides a wider dimming range subject to a constraint on the BER.

SLIPT-Enabled Multi-LED MU-MISO VLC Networks: Joint Beamforming and DC Bias Optimization

This paper studies a simultaneous lightwave information and power transfer (SLIPT)-enabled multi-user (MU) multiple input single output (MISO) visible light communication (VLC) network, where multiple user equipments (UEs) are simultaneously allowed to receive information by the photodiode (PD) and harvest energy by the solar panel, respectively. To improve the system spectral efficiency, an achievable sum rate maximization problem is formulated subject to the minimum energy harvesting (EH) requirement of each UE, the total transmit power constraint of the LEDs and the dimming control constraint of the LEDs, by jointly optimizing the beamforming vector and the direct current (DC) bias vector of the LEDs. To be general, the practical non-linear EH model and the information capacity model of the VLC channel are adopted. To solve the non-convex optimization problem, the objective function is equivalently transformed at first by using the epigraph reformulation, and then the transformed problem is relaxed with the semi-definite relaxation (SDR) method. Based on this, an iterative algorithm is designed to approximately obtain the maximal achievable sum rate based on the successive convex approximation (SCA). Simulation results indicate that there exists a non-trivial trade-off between the achievable sum rate and the harvested energy, and that DC bias vector dominates the amount of the harvested energy compared with the beamforming vector. Besides, for a given relatively high EH requirement, the achievable sum rate increases with the increment of the dimming level, especially for relatively small dimming level. Once the dimming level is larger than a specific value, with the increment of the dimming level, more transmit power will be allocated for illumination, resulting in the decrement of the achievable sum rate.

A Fuzzy Logic-Based Tuning Model in an Indoor Lighting System for Energy and Visual Comfort Management

This paper proposes a fuzzy logic-based tuning model (FLTM) for daylight-linked control of the lighting system in an office room. The proposed FLTM considered a new method of dimming levels of light-emitting diode (LED) luminaires updating process to improve the performance of the developed fuzzy logic controller (FLC) in terms of energy consumption and visual comfort metric and, at the same time, fully complies with the European Standard EN 12464-1. The artificial lighting system and daylight simulation were carried out using DIALux to model artificial lighting and daylight illuminance levels matrices. The proposed FLTM was developed and simulated using MATLAB and validated and compared with other controllers, including developed FLC and artificial neural network (ANN) based control. The simulation results showed that the proposed FLTM successfully improved the performance of developed FLC in terms of a fully satisfied visual comfort set-point. It also attained higher energy savings of 2% than ANN and achieved the closest to preset visual comfort compared with other controllers. Moreover, the proposed method consumes less computational effort, and it is easy to integrate with developed FLC and daylight-linked control of the lighting system.

Dim artificial light at night alters immediate early gene expression throughout the avian brain.

Artificial light at night (ALAN) is a pervasive pollutant that alters physiology and behavior. However, the underlying mechanisms triggering these alterations are unknown, as previous work shows that dim levels of ALAN may have a masking effect, bypassing the central clock. Light stimulates neuronal activity in numerous brain regions which could in turn activate downstream effectors regulating physiological response. In the present study, taking advantage of immediate early gene (IEG) expression as a proxy for neuronal activity, we determined the brain regions activated in response to ALAN. We exposed zebra finches to dim ALAN (1.5 lux) and analyzed 24 regions throughout the brain. We found that the overall expression of two different IEGs, cFos and ZENK, in birds exposed to ALAN were significantly different from birds inactive at night. Additionally, we found that ALAN-exposed birds had significantly different IEG expression from birds inactive at night and active during the day in several brain areas associated with vision, movement, learning and memory, pain processing, and hormone regulation. These results give insight into the mechanistic pathways responding to ALAN that underlie downstream, well-documented behavioral and physiological changes.

The Performance Comparison of SC-PPM Receiver Models

Visible light communication (VLC) technology has arisen as promising candidate to solve the critical challenges of wireless communication networks. In particular, the evolving explosion in use of internet services requiring high bandwidth will soon become a great potential problem among the service provider. Meanwhile, this paper describes a physical layer solution to provide data transmission in the VLC networks. In the paper, it is aim to examine the performance comparison of SC-PPM (Subcarrier Pulse Position Modulation) demodulator schemes. It is considered three receiver techniques to assemble the demodulator techniques to SC-PPM receiver system. Firstly, the traditional PPM (T-PPM) demodulator has been applied on the SC-4PPM receiver system to estimate the slot that includes high frequency signal that is referred to as subcarrier signal. To successfully detect the bits by using traditional PPM receiver, it must be known the dimming level of received SC-4PPM signal. This is a serious problem to ensure data transmission in the real-time VLC systems due to challenge of providing the variable dimming level knowledge at the receiver side. In another receiver model that is referred to as PD (Peak Detector), it is aim to detect peak values of slot with high frequency signal. The disadvantage of this system is that BER (Bit Error Rate) performance depends the difference between peak and bottom values of subcarrier filled slot. Hence, second method is improved to achieve the similar BER performance at all dimming levels between 12.5% and 87.5%. This receiver model is called as IPD in the paper. In brief, it is reported for the first time, it has been employed the PD and the IPD algorithms for the SC-PPM receiver schemes. In addition to this, it is given a theoretical framework for both the traditional PPM and the improved receiver schemes in VLC-SC-PPM schemes. Moreover, it has been investigated how the SC-PPM receiver schemes are affected by brightness level.

Highly Sensitive SPAD-Based Receiver for Dimming Control in LiFi Networks

Visible light communication (VLC) is an emerging mode of wireless communication that supports both illumination and communication. One essential function of VLC systems is the dimming control, which requires a sensitive receiver for low-light conditions. The use of an array of single-photon avalanche diodes (SPADs) is one promising approach to enhancing receivers’ sensitivity in a VLC system. However, because of the non-linear effects brought on by the SPAD dead time, an increase in the brightness of the light might degrade its performance. In this paper, an adaptive SPAD receiver is proposed for VLC systems to ensure reliable operation under various dimming levels. In the proposed receiver, a variable optical attenuator (VOA) is used to adaptively control the SPAD’s incident photon rate according to the instantaneous received optical power so that SPAD operates in its optimal conditions. The application of the proposed receiver in systems with various modulation schemes is investigated. When binary on–off keying (OOK) modulation is employed due to its good power efficiency, two dimming control methods of the IEEE 802.15.7 standard based on analogue and digital dimming are considered. We also investigate the application of the proposed receiver in the spectral efficient VLC systems with multi-carrier modulation schemes, i.e., direct current (DCO) and asymmetrically clipped optical (ACO) orthogonal frequency division multiplexing (OFDM). Through extensive numerical results, it is demonstrated that the suggested adaptive receiver outperforms the conventional PIN PD and SPAD array receivers in terms of bit error rate (BER) and achievable data rate.

Influence of Headlight Level on Object Detection in Urban Traffic at Night

The purpose of this work is to determine the influence of the low beam intensity of motor vehicle headlights on detection conditions in urban traffic. For this purpose, studies with fourteen subjects are conducted on three differently illuminated test roads, in which the low beam intensity is dimmed from off to fully on. At each dimming level, the subjects indicate whether or not they have detected the object, which is realized by a flat target and occurs at sixteen different positions in front of the vehicle. In addition, considerations of the contrast curve and the visibility level are made in order to determine the influence of switched off and fully switched on headlights. The results show that the negative contrast created by the existing street lighting creates detection conditions at least as good as full low beam intensity in almost all cases. The results further indicate that the influence of the low beam intensity increases with decreasing distance to the object and decreasing illumination levels. The results of this work show that an increase in low beam intensity initially leads to poorer detection conditions; thus, the option of reducing low beam intensity should be considered in urban traffic space.

Prediction of LED luminaire spectral power distribution using a mathematical model developed based on interpolation method

LED luminaires with controllable luminous flux are increasingly used, mainly due to the need to reduce electricity consumption, which is the equivalent of improving the energy efficiency of a lighting installation. Changing the dimming level changes the spectral power distribution of the luminaire or light source. Knowledge of dimming characteristics including spectral power distribution relationships provides the opportunity to optimize control algorithms and predict the impact of lighting parameters on the work surface. The paper presents a mathematical model to calculate the spectral power distribution of an LED luminaire for any level of dimming. Two interpolation methods were used to develop the model, fitted by polynomial functions and spline functions. Validation of the model was performed for two values of control voltage-dimming levels. Full Text: PDF ReferencesJ. Silva, J.F.G. Mendes, L.T. Silva, "Assessment Of Energy Efficiency In Street Lighting Design", WIT Transaction on Ecology and the Environment 129, 705 (2010). CrossRef A. Nardelli, E. Deuschle, L.Dalpaz de Azevedo, J. Lorenço Novaes Pessoa, E. Ghisi, "Assessment of Light Emitting Diodes technology for general lighting: A critical review", Renewable and Sustainable Energy Rev. 75, 368 (2017). CrossRef O. Rabaza, D. Gómez-Lorente, F. Pérez-Ocón, A. Peña-García, "A simple and accurate model for the design of public lighting with energy efficiency functions based on regression analysis", Energy 107, 831 (2016). CrossRef S. Raggiunto, A. Belli, L. Palma, P. Ceregioli, M. Gattari, P. Pierleoni, "An Efficient Method for LED Light Sources Characterization", Electronics 8(10), 1089 (2019). CrossRef I. Rachev, T. Djamiykov, M. Marinov, N. Hinov, "Improvement of the Approximation Accuracy of LED Radiation Patterns", Electronics 8, 337 (2019). CrossRef

Soft Switched Full‐Bridge DC-DC LED Driver For Street Lighting

With the availability of DC grid, DC fed light emitting diode (LED) drivers need development for both low and high voltages. An efficient DC grid based LED driver is proposed for street lighting application. As the proposed configuration is with full-bridge, it is suitable with low as well as high voltage inputs and also for higher wattage lighting. Each LED load is connected across switching devices of the full-bridge configuration. The devices of the proposed configuration handle small amount of current resulting in lower conduction losses. ZVS operation is also achieved resulting in overall high efficiency. Other advantages of this configuration include lower component count, PWM dimming and possibility for extension to more loads. Analysis and operation of the driver are presented in detail. A 145 W LED driver is developed and experimentally validated for ± 5% changes in supply voltage and at different dimming levels. The peak efficiency of the proposed driver is 95.76% at full illumination level.

True specs for dimmed and colour tuned LED luminaires

Colour tunable and dimmable LED lamps and LED luminaires are used increasingly in both domestic and professional lighting sector. The documentation of energy and light quality performance are often very limited for only for a single setting of multiple possible settings. Fifteen LED lamps and eight LED luminaires that are dimmable and tuneable white have been selected for demonstration of the variations in these parameters and possible errors in lighting design simulations. These have been tested in over twenty modes of operation including dimming from 100% to 25%, and correlated colour temperature (CCT) settings from 2200K to 6500K. The inherent standby power of these colour tuneable devices is measured, and the overall efficacy is evaluated in normal usage situations. In average for all tested LED lamps and luminaires 49% and 33% of the energy consumption is used in standby mode for 1h and 2h on time pr. day, respectively. The extensive set of test results show that there can be very large variations in e.g. the luminous flux, luminous efficacy and stroboscopic visibility measure (SVM), while others are very consistent over the modes of operation. The luminous flux shows variations of down to 22% of the maximum and rated value, and these lowest values occurs at the lowest CCT. The best performing has over 90% at all CCT settings. For the luminous efficacy most test results show a maximum value at 4000K or at the maximum CCT, and variations down to 20-50% of the maximum efficacy. The SVM is shown to increase to values over 1 and up to 2.4 at low dimming levels or low light output, demonstrating that stroboscopic effect will be visible for the majority of people and hence a problem in such settings. This is seen for approx. half the tested while the others have SVM < 0.4 for all settings and will not be visible over all settings. These results demonstrate the need for testing over the possible modes of operation to be able to correctly design and simulate a lighting installation using dimmable and colour tunable LED lamps and luminaires. The needed new dataformats and adoption of these from test laboratories to lighting software, in order for lighting designers and energy engineers to be able to make use of the extensive test results, are discussed.

The Effect of High, Partial, and Low Multisensory Congruity between Light and Scent on Consumer Evaluations and Approach Behavior

Ambient light is inherent in the store environment, making research on the interaction effects between light and other atmospheric cues crucial to understanding how the store environment can affect consumers. This study extends existing research on multisensory congruity effects between atmospheric cues by examining whether multiple sensory associations (i.e., warmth and brightness) of ambient cues (i.e., light and scent) must match to create positive effects on consumer evaluations and behavior or whether a match of only one sensory association is sufficient. Previous research operationalized multisensory congruity primarily via the match on one specific association; however, the results of our two studies show that matching ambient light and scent (compared to a mismatch between the stimuli or compared to only one ambient cue) only led to enhanced evaluations and approach behavior when these stimuli were matched on both their perceived association with a warm or cold temperature and with a dim or bright illuminance level. Our research supports the importance of perceiving the store environment holistically and suggests that the description and selection of an atmospheric cue to create positive congruity effects on consumer evaluations and behavior is quite complex.

Enhanced ADO-OFDM-based adaptive digital dimming VLC system.

Visible light communication (VLC) has shown significant growth in recent years. VLC simultaneously offers illumination and communication. In VLC systems, dimming control is used to handle the lighting and energy consumption constraints. In this paper, a new, to the best of our knowledge, adaptive digital dimming optical-orthogonal frequency division multiplexing (ADDO-OFDM) based on pulse width modulation is proposed to combine enhanced asymmetrically clipped DC biased optical OFDM (EADO-OFDM) and negative EADO-OFDM (ENADO-OFDM). It exploits the performance benefits of EADO-OFDM and ENADO-OFDM. The proposed ADDO-OFDM controls the dimming level in a vast range with an acceptable bit error rate with a favorable data length.

Joint LED Selection and Precoding Optimization for Multiple-User Multiple-Cell VLC Systems

This paper proposes a hybrid dimming scheme based on joint LED selection and precoding design (TASP-HD) for multiple-user (MU) multiple-cell (MC) visible light communications (VLC) systems. In TASP-HD, both the LED selection and the precoding of each cell can be dynamically adjusted to reduce the intra- and inter-cell interferences while satisfying illumination constraints. First, a MU-MC-VLC system model is established, and then a sum-rate maximization problem under dimming level and illumination uniformity constraints is formulated. In this studied problem, the indices of activated LEDs and precoding matrices are optimized, which result in a complex non-convex mixed integer problem. To solve this problem, the original problem is separated into two subproblems. The first subproblem, which maximizes the sum-rate of users via optimizing the LED selection with a given precoding matrix, is a mixed integer problem solved by the penalty method. With the optimized LED selection matrix, the second subproblem which focuses on the maximization of the sum-rate via optimizing the precoding matrix is solved by the Lagrangian dual method. Finally, these two subproblems are iteratively solved to obtain a convergent solution. Simulation results verify that in a typical indoor scenario under a dimming level of 70%, the mean bandwidth efficiency of TASP-HD is 4.8 bit/s/Hz and 7.13 bit/s/Hz greater than AD and DD, respectively.

A power-efficient self-calibrating smart lighting system

Lighting load accounts for a significant portion of overall energy consumption in office buildings. To reduce this load, we have designed and built a smart self-calibrating lighting control system that minimizes power consumption that automatically responds to changes in daylight and occupancy, while simultaneously providing personalized lighting comfort to each occupant. The system measures illuminance and occupancy from sensors located at each work station. Using an unobtrusive self-calibration process, it estimates the relationship between the dimming level of each bulb and the illuminance at each work station. Subsequently, an adaptive control algorithm maintains the desired illuminance at work surfaces despite environmental fluctuations by periodically recalculating the power-efficient and comfort-preserving dimming level for each bulb. Based on a realistic deployment of our system, we find that our system quickly responds to changes in occupancy, daylight and user preferences. We also show, through extensive simulations using 7 months of collected daylight and occupancy data, that our system reduces energy consumption by about 40% compared to conventional LED lighting systems.

Variable pulse position modulation receivers for visible light communication systems without the knowledge of dimming level

AbstractThe dimming control is one of the most significant issues to provide both illumination and data transmission for visible light communication (VLC) systems. The receivers—such as variable pulse position modulation (VPPM) receiver—must know the dimming level of the received signal for the demodulation process. To provide a complete solution to this problem, we propose two VPPM receivers that can detect data bits without knowledge of dimming level (KDL). The first one, which is referred to as artificial neural network (ANN)‐VPPM, includes the ANN technique to achieve a proper step signal instead of traditional mask signals that are generated by using the perfect KDL. The ANN‐VPPM gives a successful bit error rate (BER) performance compared to the unsuitable traditional system (U‐TS), which is called the traditional system that decodes the VPPM signal using inappropriate mask signals. If the ANN‐VPPM is compared to traditional system (TS), which is the traditional system using a perfect mask signal, the TS has better BER performance than the ANN‐VPPM. Hence, the other one that is called the proposed estimation method (PEM) is improved to achieve the same BER performance compared to the TS. An estimation performance is given to indicate the 100% estimation rate and to prove that the BER performance of systems is the same at least signal‐to‐noise ratio of 22 dB. Additionally, the PEM is saving the optical power of the VPPM signal up to 23% at a BER of 10−3 when compared to U‐TS.

Model predictive lighting control for a factory building using a deep deterministic policy gradient

This paper presents an integrated lighting control that employs a daylit illuminance prediction model for a large, open-spaced factory building in which interactions between multiple luminaires and points of the workplane exist. The prediction model was developed with Radiance and consists of daylight and electric lighting prediction components. Both components showed reliable accuracy after calibration with measured illuminance (daylighting: MBE = 4.9%, CVRMSE = 24%; electric lighting: MBE = 3.7%, CVRMSE = 7.7%). An optimal policy trained by the deep deterministic policy gradient determines the dimming levels of multiple luminaire groups. The policy is developed with an artificial neural network model whose input is the current state (daylight distribution) and whose output is an action (lighting control variables). The model could provide an appropriate amount of electric lighting that meets the target illuminance and uniformity, while only 54% of the average consumption power (7,292 W) was needed compared with that of the existing rule-based control (13,629 W).

소규모 사무실에서 포토센서 기반 디밍시스템의 성능에 대한 제어 알고리즘의 영향

This study discusses the system performances of photosensor-based dimming controls in a small office with a lightshelf. Computer simulations using the Lightscape software were conducted for a variety of daylight conditions. Four control algorithms were employed, and partially-shielded and unshielded photosensors were used to predict dimming levels. Results indicate that control algorithms containing constant and power functions caused excessive dimming and failed to achieve target illuminance under all sky conditions. A linear algorithm showing relatively insensitive dimming levels to photosensor illuminance was appropriate to achieve the optimum system performance under clear sky, when the photosensor was partially-shielded. In this case, the lighting energy savings ranged from 33.3 % to 74.5 %. The system performance of dimming control based on the four algorithms under overcast sky provided excessive dimming and led to failures of controls. The unshielded photosensors failed to provide the target illuminance under the majority of conditions. The linear regression models between the outdoor global daylight illuminance and photosensor illuminance due to daylight were statistically meaningful with strong correlations.