Dimmable Light-emitting Diode Research Articles

Growth and Agronomic Traits of Green Onion under the Agrovoltaic System with Red Supplemental LED Lighting

Background and objective: An agrovoltaic system is a power generation method applying photovoltaics (PV) to crops cultivated on a farm. Usually, the PV system covers less than 30% of the upper surface of crops on the ground. If the PV system covers the upper layer of the crops, the yield will decrease by 15-20% due to the shading of the PV module. This study was carried out to investigate the effects of red supplemental light-emitting diode (LED) lighting under the PV system on growth and agronomic traits of green onions.Methods: To resolve the issue about decreasing yield, we constructed a 50 kW agrovoltaic system with the red (660 nm peak) LED dimming facility on the farm with 3 different plots for comparison. The 1<sup>st</sup> was PV + LED (two parts of dimming area: 3 hours and 6 hours). The second was only PV, and the last was a reference for comparison of yield (control plot). We transplanted uniform seedlings of green onions on three areas of the farm on June 23, 2020. We used red LED lighting for 3 hours and 6 hours after sunset and harvested green onions on October 25, 2020. We used less than 1% of electricity of total power generated by the agrovoltaic system for supplemental LED lighting.Results: The result of harvesting under the agrovoltaic system with 3 hours of lighting showed that there was 38% more yield than the control plot. We also discovered the optimal amount of supplemental LED lighting because even 6 hours of lighting were not better than 3 hours.Conclusion: Applying supplemental LED lighting after sunset can compensate for the yield decrease. The LED supplemental lighting for 3 hours is optimal for crop harvest. We expect that this system can be helpful to farmers who want to construct an agrovoltaic system.

A Supplemental Lighting Control Approach in Controlled Environment Agriculture to Reduce Peak Power Consumption

Global population growth requires efficient food production, especially with food security concerns due to natural resources limitation and climate constraints. Supplemental lighting is an effective means of increasing productivity in greenhouses. However, supplemental lighting electricity cost can be high, and systematic lighting strategies are required to reduce lighting electricity cost. Prior research has focused on minimizing electricity use or cost, while maintaining adequate crop growth. However, in addition to being charged for electricity consumption, US greenhouse growers also pay a demand charge that is based on the peak electricity use during a 15-min period within each billing cycle. This demand charge is in the same order of magnitude as the charge for the used electricity, but has been ignored in prior lighting optimization research. This paper presents a lighting strategy for controlled environments (like greenhouses) equipped with dimmable light-emitting diodes (LEDs) to minimize supplemental lighting electricity cost and peak power consumption of supplemental lighting. Markov-based sunlight prediction is employed to develop a realistic control strategy and improve its efficiency. Moreover, the impact of shifting the time of day during which supplemental lighting is used on peak power consumption is investigated. Compared to a heuristic method, the proposed method illustrates an up to 51% mean peak reduction.

Smart Dimmable LED Lighting Systems.

This paper proposes energy-efficient solutions for the smart light-emitting diode (LED) lighting system, which provides minimal energy consumption while simultaneously satisfying illuminance requirements of the users in a typical office space. In addition to artificial light from dimmable LED lamps, natural daylight coming from external sources, such as windows, is considered as a source of illumination in an indoor environment. In order to reduce total energy consumption, the smart LED system has the possibility to dim LED lamps, resulting in reduced LED output power. Additionally, various LED lamps' functionality, such as semi-angle of the half illuminance and LED tilting, are introduced as an additional parameter to be optimized to achieve greater energy saving of the designed system. In order to properly exploit external lighting, the idea to reduce overall daylight intensity at a users' location is realized by the option to dim the windows with a shading factor. Based on the users' requirements for a minimal and desired level of illumination, the proposed optimization problems can be solved by implementing different optimization algorithms. The obtained solutions are able to give instructions to a smart LED system to manage and control system parameters (LEDs dimming levels, semi-angles of the half illuminance, orientation of LEDs, the shading factor) in order to design total illumination, which ensures minimal energy consumption and users' satisfaction related to illuminance requirements.

SEPIC Converter for Low Power LED Applications

Due to the development in light Emitting Diode (LED), white LED are on the whole utilized in homes, industries and business regions to replace the heated bulbs, non metalic bulbs, and even compact fluorescent lamp(strength saving lamp). The primary choices in those applications are high strength factor, and coffee harmonics. The input line cutting-edge harmonics is decreased and power aspect is high. in order to manipulate the LED brightness a current remarks loop is brought. The benefits of the circuit are strength conversion, no want to sense the enter voltage, voltage step-up and down, simple feedback manage, excessive electricity component and dimmable LED present day. LED performs a critical function within the enterprise and in our existence. The SEPIC converter is to increase the efficiency of LEDs and get the better overall performance than the opposite lighting fixtures utility. There are numerous reasons for the fluctuations inside the deliver voltage, here propose the use of sepic converter this could triumph over that via giving us the deliver voltage without the fluctuation.

Estimating the quantum requirements for plant growth and related electricity demand for LED lighting systems

Indoor plant production systems with artificial lighting are considered an emerging technology contributing to biomass-based value webs. The viability of this concept greatly relies on the energy requirements (ER, Watt) for lighting. We estimated the ER for plant growth by calculating the conversion efficiency of electricity to light of solid-state light-emitting diodes (LED) and the quantum requirements for plant growth of a fictional plant stand producing 2500 g of dry weight per m2 of ground during 100 days, representing a high productivity benchmark of field crops. The quantum output (µmol s−1 W−1) of eight LEDs of different colours varied between 0.78 for green and 2.54 for deep red. Uncertainty in the H+ demand for ATP synthesis during photosynthesis, the relative portion of photorespiration and the fraction of light intercepted by plant canopies (fabs) were considered in a pessimistic (PA) and optimistic (OA) approach of calculation of ER. Cumulative ER were 606 and 265 kWh m−2 for the PA and OA scenarios. The energy conversion efficiencies in the PA and OA scenarios were 2.07 and 4.72%. Estimates of energy savings by suppressing photorespiration and increasing fabs vary between 24 and 38%. The peak daily ER were 9.44 and 4.14 kWh in the PA and OA scenarios. Results are discussed in the context of the design of lighting in indoor plant production systems and commercial greenhouses where natural fluctuation in solar radiation could be balanced by dimmable LED panels.

Characterization of Commercial LED Lamps for Power Quality Studies

Light emitting diode (LED) lamps exhibit nonlinear characteristics causing a negative influence on the power grid and on public health. High harmonic contents injected by LEDs as well as their sensitivity to voltage fluctuations in the network should be further examined. This article aims at achieving a better understanding of the characterization of commercial dimmable LED lamps and their impact on power quality (PQ) parameters. A testbed has been implemented as a platform to investigate the current and voltage quality issues by conducting various experimental tests that include PQ concerns such as harmonic analysis, voltage flickering, voltage sag, and voltage swell. The experimental setup allows the execution of light intensity, harmonic current contents, and voltage measurement of commercial LED lamps. Data processed using the MATLAB software tool have been used to analyze the results. The percent flicker is used to evaluate varying degrees of flickering happening in LED lighting networks. The effect of changing the light intensity for dimming purposes on the perceptibility of flicker has been studied and discussed as well. This article provides a solid reference for researchers working on the PQ improvement of LED lamps.

Li-Fi delivering broad band and multimedia content under dimming in train

This paper focuses in delivering broad band and media content to numerous users while traveling in the train through light fidelity (Li-Fi), an innovative technology under Visible Light Communication (VLC). In our daily life, there is increasing traffic request for open Radio Frequency (RF) to support the users. In RF, even recurrence and spatial reuse of spectrum not able to support in conveying broad band and multimedia content to the internet users. For high-capacity mobile data networks, the VLC can balance the RF-based mobile communication systems. VLC conserves energy through dimming. Dimmed Light Emitting Diode (LED) luminaries provide visual comfort with appropriate optics while accessing internet. In the proposed work, LED dimming is achieved through digital dimming modulation technique, Variable Delta Sigma Modulation. The broad band and multimedia content can be delivered faster through Reverse Polarity Optical Orthogonal Frequency Division Multiplexing modulator to the internet users under dimming with better bit error rate and bit rate.

Longer Photoperiods with the Same Daily Light Integral Improve Growth of Rudbeckia Seedlings in a Greenhouse

Supplemental light can increase growth and accelerate production of greenhouse crops, but it can be expensive if not provided in a way that promotes efficient use of the light. Dimmable light-emitting diode (LED) fixtures have the potential to reduce lighting costs because the output can be precisely controlled to meet crop needs. Because light is used more efficiently to drive photosynthesis at lower photosynthetic photon flux densities (PPFDs), we hypothesized that providing Rudbeckia fulgida var. sullivantii ‘Goldsturm’ seedlings with the same daily light integral (DLI), spread out over a longer photoperiod and at lower PPFDs, should improve growth. A DLI of 12 mol·m−2·d−1 was provided in a greenhouse over 12, 15, 18, or 21-hour photoperiods from a combination of sunlight and supplemental light from LEDs, using adaptive lighting control. Plants grown without supplemental light had an ≈12-hour photoperiod and received an average DLI of 5 mol·m−2·d−1, ≈58% less light than the four lighting treatments. Lengthening the photoperiod from 12 to 21 hours increased shoot dry mass (30%), root dry mass (24%), plant height (14%), leaf area (16%), and chlorophyll content index (48%), and decreased specific leaf area (26%). There was no significant effect of photoperiod on root mass fraction or compactness. Growth parameters of plants without supplemental light were 26% to 90% smaller compared with those in the 12-hour photoperiod treatment. Treatment effects on canopy size, seen as early as 2 weeks into the study, were correlated with final shoot dry mass. Longer photoperiods did not induce a shade-avoidance response, based on specific leaf area and compactness data. The 24% increase in root dry mass for the plants in the 21-hour photoperiod suggests that cropping cycles can be shortened by 1 to 2 weeks compared with the 12-hour photoperiod. This could result in more crop turns per year and increased profits. In addition, fewer lights would be needed for adequate growth, reducing the capital cost of the lighting system.

Single-Stage Three-Phase AC-DC Resonant Switched Capacitor LED Driver Without Electrolytic Capacitor and Reduced Number of Controlled Switches

This article proposes a three-phase resonant driver based on the resonant switched capacitor (RSC) for the light emitting diode (LED). The employed LED is chip-on-board (COB) based technology, resulting in a high power density. As the driver provides low current ripple and low flicker, it is not necessary to use electrolytic capacitor. This characteristic improves the driver lifetime. The two controlled switches operate under zero current switching (ZCS), which increases the driver efficiency. The LED dimming is enabled, only by varying the switching frequency. A 216 W laboratory prototype was designed to supply a LED device from an AC 220 V (60 Hz) voltage source. The LED driver is presented and discussed. Experimental results have shown power factor higher than 0.98, the percent flicker of 6.6% at 360 Hz and the efficiency of is 89%.

AC–DC Flyback Dimmable LED Driver with Low-Frequency Current Ripple Reduced and Power Dissipation in BJT Linearly Proportional to LED Current

In this paper, a dimmable light-emitting diode (LED) driver, along with the low-frequency current ripple decreased and the bipolar junction transistor (BJT) power dissipation reduced, is developed. This driver is designed based on a single-stage flyback converter. On the one hand, the low-frequency output current ripple reduction is based on the physical behavior of the linear current regulator. On the other hand, when the voltage across the LED string is decreased/increased due to dimming or temperature, the output voltage of the flyback converter will be automatically regulated down/up, thereby making the power dissipation in the BJT linearly proportional to the LED current. By doing so, not only the power loss in the linear current regulator will be decreased as the LED current is decreased or the LED temperature rises, but also the output current ripple can be reduced. Furthermore, the corresponding power factor (PF) is almost not changed, and the total harmonic distortion (THD) is improved slightly. In addition, the LED dimming is based on voltage division. Eventually, a 30 W LED driver, with an input voltage range from 85 to 295 Vrms and with 24 LEDs in series used as a load, is developed, and accordingly, the feasibility of the proposed LED driver is validated by experimental results.

Enhancing City Sustainability through Smart Technologies: A Framework for Automatic Pre-Emptive Action to Promote Safety and Security Using Lighting and ICT-Based Surveillance

The scope of the present paper is to promote social, cultural and environmental sustainability in cities by establishing a conceptual framework and the relationship amongst safety in urban public space (UPS), lighting and Information and Communication Technology (ICT)-based surveillance. This framework uses available technologies and tools, as these can be found in urban equipment such as lighting posts, to enhance security and safety in UPS, ensuring protection against attempted criminal activity. Through detailed literary research, publications on security and safety concerning crime and lighting can be divided into two periods, the first one pre-1994, and the second one from 2004–2008. Since then, a significant reduction in the number of publications dealing with lighting and crime is observed, while at the same time, the urban nightscape has been reshaped with the immersion of light-emitting diode (LED) technologies. Especially in the last decade, where most municipalities in the EU28 (European Union of all the member states from the accession of Croatia in 2013 to the withdrawal of the United Kingdom in 2020) are refurbishing their road lighting with LED technology and the consideration of smart networks and surveillance is under development, the use of lighting to deter possible attempted felonies in UPS is not addressed. To capitalize on the potential of lighting as a deterrent, this paper proposes a framework that uses existing technology, namely, dimmable LED light sources, presence sensors, security cameras, as well as emerging techniques such as artificial intelligence (AI)-enabled image recognition algorithms and big data analytics and presents a possible system that could be developed as a stand-alone product to alert possible dangerous situations, deter criminal activity and promote the perception of safety thus linking lighting and ICT-based surveillance towards safety and security in UPS.

A High-Power-Factor Dimmable LED Driver with Integrated Boost Converter and Half-Bridge-Topology Converter

This paper proposes a dimmable light-emitting diode (LED) driver featuring a high power factor and zero-voltage switching on (ZVS). The circuit is obtained by integrating a boost converter and a dc-dc converter with half-bridge topology. The high power factor is achieved by operating the boost converter in discontinuous current mode (DCM). The LEDs are dimmed by the control scheme of asymmetrical pulse-width modulation (ASPWM). The developed circuit eliminates the inherited dc-offset current of the transformer in a conventional asymmetrical half-bridge converter by introducing a balance capacitor. Both active switches can operate at ZVS by freewheeling the boost inductor current and the transformer magnetizing current to discharge the energy stored in their parasitic capacitance. The circuit operation is analyzed in detailed, and mathematical equations are derived. Finally, a 115-W prototype circuit for driving high brightness LEDs was built and tested. The experimental results verify the feasibility of the proposed LED driver with satisfactory performance. It can achieve a high power factor and ZVS operation.

A Study on the Multiple Control Techniques for LED Dimming of Single Stage LLC Resonant Converter

This paper proposes the multiple control techniques for light emitting diode (LED) dimming of a single stage LLC resonant converter. In recent years, LEDs have emerged as a new next-generation light source and replaced conventional lighting devices such as incandescent and fluorescent lamps. Further, the use LEDs is increasing in many fields owing to their versatility and other advantages. However, LEDs are not available in commercial power; therefore, a driver circuit is required. Accordingly, the interest in LED driving circuits has increased, and there is an increasing demand for higher efficiency and further maximizing light efficiency and lifetime. A typical LED driver circuit comprises of two stages, i.e., a power-factor correction (PFC) stage and a DC/DC converter stage. This configuration results in unnecessary losses, in addition to the drawback in terms of a large driving-circuit volume. Further, when the conventional PWM dimming method is applied to an LLC resonant converter, there is a limit on the usable frequency range. The frequency cannot be indefinitely increased because the switching frequency is inversely related to the output characteristic. Thus, dimming function over a wide range is impossible. Therefore, to improve the overall efficiency of a LED driver circuit, a single-stage configuration is used to reduce the number of devices that cause unnecessary loss, and an asymmetric converter is used to reduce the voltage stress across the switch. Additionally, this paper proposes a converter circuit with a wider dimming range and PFC function through frequency-control, switching ratio control, and upper switching ON/OFF control.

A Turn-off Delay Controlled Bleeder Circuit for Single-Stage TRIAC Dimmable LED Driver With Small-Scale Implementation and Low Output Current Ripple

A single-stage TRIAC (TRIode for alternating current switch) dimmable LED (light emitting diode) driver using a buck converter fed through a capacitor input rectifier provides many advantages such as small-scale implementation, low output current ripple, and stable dimming operation. This circuit topology, however, has a serious issue: A large inrush current to the smoothing capacitor. To solve this issue, this paper focuses on a bleeder circuit in the TRIAC dimmable LED driver. This paper presents the mechanism of the large inrush current issue and its relationship to a conventional bleeder circuit. Moreover, this paper proposes a turn-off delay controlled bleeder circuit. The proposed bleeder circuit is analyzed by using its discrete-time state-space model in order to set proper circuit parameters for inrush current reduction. Experimental results demonstrate the inrush current reduction by the proposed method, which leads to a 37% reduction of maximum input current, as well as proper dimming operation and low output current ripple. The proposed method achieves further small-scale implementation, which enhances the advantages of the intended main circuit topology.

A Remotely Central Dimming System for a Large-Scale LED Lighting Network Providing High Quality Voltage and Current

Standard TRIAC-based dimmers introduce power quality issues especially for a large-scale lighting network. Other existing dimming protocols involve additional wiring systems and/or additional controllers to light emitting diode (LED) drivers. This paper proposes a central dimming system for a large penetration of LED lamps. The dimming system is remotely controlled through a webpage or a desktop application. Dimming is achieved while maintaining high voltage and current quality waveforms, which results in a high power factor and a low input current harmonic distortion. The system does not require additional wiring or specific adjustments to commercial dimmable LED drivers. The system allows scheduling a dimming profile to endorse energy saving. In the proposed dimming system, dimming function is achieved by connecting a voltage source converter (VSC) between the grid and the LED lamps. An advanced feature is added to the VSC dimmer to remotely send/receive messages between the system and the user through a graphical user interface. Thus, the user can communicate with the VSC dimmer by sending commands and receiving feedback information. The influence of communication delay on system stability is analyzed by using small signal models. A VSC dimmer prototype (500 VA/120 V) has been built with a communication module to provide remote control. Experimental results and comparisons between utilizing the TRIAC-based dimmer and the VSC dimmer for dimming function are discussed in the paper.

Energy-Efficient Supplemental LED Lighting Control for a Proof-of-Concept Greenhouse System

In this paper, a multiple-input multiple-output control system integrated with daylight harvesting is presented as a proof-of-concept system for energy-efficient greenhouse lighting. The control objective is to regulate the intensity of dimmable multispectrum light-emitting diode (LED) fixtures for achieving desired spectral irradiance levels and color ratios while utilizing the natural sunlight as much as possible. To ensure stability and improved dynamic performance, a Smith predictor is utilized to compensate for the delay introduced into the system by the communication hardware. A stability analysis of the closed-loop system is presented considering system delay and modeling uncertainties. The proposed control system was experimentally tested in a grow-tent environment consisting of dimmable halogen lights that emulate daylight variation, multispectrum dimmable LED fixtures, and low-cost light sensors. The results indicate that about 30% energy savings can be achieved by using the proposed automated lighting control system.

Multi‐channel LED driver based on switched‐controlled capacitor with constant frequency control

Current sharing among light-emitting diode (LED) strings is significant for reliability and long life. The capacitive balancing was widely used with low losses and small volume. However, the capacitive balancing scheme adopting the impedance matching causes large circulating current, and its precision of current sharing is restricted due to impedance tolerance. In addition, the high reactive power with pulse frequency control brings high power stress on the volt-ampere rating (VAR) of the half-bridge switches and arouses heavy electro-magnetic interference. In this study, the interleaved structure of the upper and lower half-bridge is proposed to alleviate the mismatching of capacitance impedance. Besides, the wide range of LED dimming capability is accomplished by using the switched-controlled capacitor (SCC) unit with the constant frequency of power switches. The circuit analysis, SCC modulation, current sharing, LED dimming and performance comparisons are examined in detail. All the superior performance of the proposed LED driver is verified by simulation prototype and experimental platform with four-channel LED strings and rated power of 23 W. The accordance of theoretical analysis, simulation waveforms and experiment results further confirms the feasibility of the proposed LED driver.

Drain-Voltage Balance and Phase-Shifted PWM Control Schemes for High-Efficiency Parallel-String Dimmable LED Drivers

An LED driver consisting of dimmable current balancing circuits (CBCs) and a boost converter with drain voltage balance (DVB) and phase-shifted pulsewidth modulation (PSPWM) control schemes is presented. To reduce the power loss on conventional linear current regulators, CBCs are employed. The DVB control scheme is proposed to maintain a desired constant voltage across the CBCs, so as to increase current balance and achieve high efficiency of the CBCs. Thus, the bus voltage of the boost converter is adaptively regulated based on the DVB control. The PSPWM control scheme can alleviate the variation of the bus current provided by the boost converter. As a result, the transient ripple of the bus voltage can be reduced when the light-emitting diode (LED) strings are turned on and off. Furthermore, the utilization of DVB control is increased when the PWM dimming duty cycle becomes lower. The experimental results demonstrate that the minimum voltage among the CBCs is always kept at the lowest constant level while maintaining the required current passing through the LED strings. The efficiency of the CBCs is kept almost the same for different LED currents and is over 95%. Thus, a high-efficient parallel-string dimmable LED driver with simple circuitry can be achieved.

Wide-range dimmable LED lighting based on QL-SEPIC converter

ABSTRACTThis paper proposes quadratic-like single-ended primary inductance converter (SEPIC) converter, a DC/DC converter suitable for wide-input voltage range. This circuit can be gated at higher duty ratio compared with conventional SEPIC converter, while the voltage conversion ratio is low. This feature is beneficial for high-input voltage because it prevents the controller from falling into extremely low duty ratio limitation. A prototype circuit is implemented with Pulse-Width-Modulation (PWM) control to drive the Light emitting diode (LED) strings for demonstration of the circuit application. Recent studies have advocated LEDs as efficient and durable technology for lighting applications. A stabilized output converter is required to regulate the current flowing through the LED lamp. The dimming control of the LED light output is implemented by the controller. This converter can be powered from either a 24-Vdc battery or from the universal AC input voltage (up to 360 Vdc). Such a wide-input voltage application can be found in emergency lighting in which the light is possibly powered either from battery or AC input voltages. Experimental results prove the feasibility of the circuit topology and theoretical analysis.

LED dimming technique without frequency and pulse width modulations

SummaryIn this paper, a novel dimmable light‐emitting diode (LED) driver is implemented by a series‐parallel resonant converter. Variable resonant inductor is used for dimming purposes. This technique is not requiring switching frequency variation or pulse width modulation, unlike commonly used techniques. The proposed technique is implemented on 40 one‐watt series connected power LEDs at 60‐kHz constant switching frequency. The experimental results show that LEDs can be dimmed to a desired power level within the range of nominal and low power.