Light-emitting Diode Lighting Systems Research Articles

Study on thermal and structural stability of high power light-emitting diode lighting system.

In this paper, we have been analyzed the thermal-fluid flow and structural stress of high power Light-emitting diode (LED) lighting system for outdoor lighting. Thermal and Structural performances of LED lighting systems were designed using computer aided engineering (CAE) and after securing their structural and thermal safety, simulated in order to develop 400 W high-efficiency LED floodlight. The temperature of LED was shown to rise up to 136 degrees C. This means that the cooling system should be improved. Maximum strain was detected in the glass, yet they appeared largely safe. It is important for the design to focus on the cooling fin. Regarding the lifespan of LED, it is necessary to have a plan for minimizing errors when testing designs for optimizing air-cooling structures. Which measured the lifetime of the lighting equipment has passed.

Optimization of a merit function for the visual perception of color uniformity in spot lights

AbstractThe objective of the present study is the development of an optimized evaluation method which describes color uniformity in the far field of light‐emitting diode (LED) spot lights related to visual perception of color and pattern. The merit function is requested to evaluate measurements and optical simulations of spot light systems. A human factor experiment was performed as a two‐alternative forced choice (2AFC) test. During the experiment, a pairs of spot lights with various spatial color distributions were shown successively to the subject. The subjects had to select the more even spot light of the pair shown.The perceived rank order of spot lights was calculated afterwards. It was compared with five different mathematical functions describing several aspects of spatial color uniformity based on the CIELAB color space. These are the widely used color difference ΔE, gradient, difference of color average, circular symmetry description, and linear smoothness. No single basic function fits the perception in a sufficient way because none of the function considers all visual aspects. For a better correlation between the visual perception and the merit function, a linear combination of four basic functions is proposed. The designed merit function for the color uniformity of spot lights USL is more effective for the prediction of the visual perception. A correlation value of 0.91 is reached. It enables a quantitative evaluation of those LED lighting systems and protects against individual subjective judgments. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 287–296, 2015

Hybrid daylight/light-emitting diode illumination system for indoor lighting

A hybrid illumination method using both daylight and light-emitting diodes (LEDs) for indoor lighting is presented in this study. The daylight can be introduced into the indoor space by a panel-integration system. The daylight part and LEDs are combined within a specific luminaire that can provide uniform illumination. The LEDs can be turned on and dimmed through closed-loop control when the daylight illuminance is inadequate. We simulated the illumination and calculated the indoor lighting efficiency of our hybrid daylight and LED lighting system, and compared this with that of LED and fluorescent lighting systems. Simulation results show that the efficiency of the hybrid daylight/LED illumination method is better than that of LED and traditional lighting systems, under the same lighting conditions and lighting time; the method has hybrid lighting average energy savings of T5 66.28%, and that of the LEDs is 41.62%.

리튬 폴리머 전지를 이용한 태양광 LED 조명시스템

에너지의 고갈을 대비하여 자연을 이용한 태양에너지에 대한 연구는 매우 중대하고 필연적인 과제이다. 이와 더불어 최근 우리나라는 저탄소 녹색성장에 있어 신성장 동력산업의 일환으로 저소비전력, 환경친화적인 조명기구로 LED(Light Emitting Diode)를 선정하여 연구 개발을 촉진하고 이를 활용한 다양한 새로운 산업이 창출되고 있다. 본 개발 내용은 리튬 이온 배터리의 뛰어난 성능을 가지며 폭발 위험성이 현저히 적은 리튬 폴리머 전지를 사용한 태양광 LED 조명시스템을 개발하였다. 태양광 패널은 100W 용량으로 제작하고, 전원공급시스템은 다양한 생활전기로 사용할 수 있도록 직류(DC) 및 교류(AC) 전원을 모두 갖추어 기능상의 편의를 고려하였다. The research on solar energy that we get from nature to cope with energy exhaustion is a very significant and inevitable task for us to do. Along with this, lately, in Korea, as part of new growth engine industry regarding low-carbon green growth, we have selected the LED(Light Emitting Diode) as low power consuming, eco-friendly lighting equipment and have been facilitating research and development on it and creating a variety of new industries utilizing it. What was developed here in this research was the photovoltaic LED lighting system applying lithium polymer batteries equipped with the excellent performance of lithium ion batteries as well as significantly low explosive hazard. Its photovoltaic panel was made to have 100W capacity, and for its power supply system, functional convenience was considered so that it could be equipped with both DC and AC power to be used as household electricity in a variety of ways.

A multi-functional design approach and proposed figure of merits for solid state lighting systems

Energy has been identified as one of the most important problems during the last few years. One of energy efficient technologies may reduce consumed energy in buildings from 20 percent to less than 5 percent. A novel lighting technology has recently been evolved as light emitting diodes (LEDs) that can be over 7–10 times more efficient than conventional-old incandescent lamps. Therefore, LED lighting systems have been rapidly replacing conventional energy-hungry lighting products like incandescent lamps and more recently environmentally hazardous fluorescent lamps. While LEDs may produce large amounts of lumens, they are solid state based technologies similar to computer chips so they have to be kept cool at certain chip junction temperature. The demand for high light output LED systems lead to significant heat generation rates, so that higher heat fluxes result in elevated junction temperatures on LED chips in SSL lighting systems. Moreover, the changes on the junction temperature strongly impact the reliability, lifetime, light output and quality of the light. Because of their simplicity, reliability, low cost and silent operation, passive air-cooling systems are preferred in LED lamps. Passive metal based heat sinks are the main cooling components of typical LED lamps serves for both LEDs and driver electronics. Heat is dissipated generally from finned surfaces to ambient air with primarily convection mechanism and partially radiation. But it requires a large surface area and weight under the limitations of the standardized lamps. Thus, the optimization of the heat sink in an LED system is crucial. Developing figure of merits (FOM) is very important for designers and researchers to find the most optimal solution accounting for critical metrics such as size, weight, cost and performance. In the present study, thermal, electrical and optical experimental results of various commercial A-line LED lamps are investigated and a number of FOMs are proposed based on the performance, size and weight. Proposed FOMs aim to evaluate different aspects by combining a number of performance metrics. Results show that one can combine and analyze multi-purpose design parameters for thermal, electrical and optical performances and manufacturing for engineers and consumers.

An Approach to Reduce AC LED Flicker

In this paper, we investigate a circuit design to reduce light flicker from an alternating current (AC) lightemitting diode (LED) lighting system. AC LEDs in the commercial marketplace have been criticized for the light flicker that they produce. In general, light flicker is an unwelcome phenomenon in a lighting application because of the health hazards it may cause. Some solutions have been proposed to reduce flicker from light sources, but they suffer from issues such as low power factor, low power efficiency, or bulky size. Here we propose an approach that can effectively reduce light flicker from an AC LED lighting system while maintaining normal power factor and high power efficiency.

Applications of Intelligent Machine Vision in Plant Factory

Intelligent machine vision has been widely used in plant factory for many purposes. There are two aims in this study i.e. the first is improving the performance of intelligent machine vision for precision irrigation system using optimized feature selection technique and the second is developing intelligent machine vision for precision artificial lighting system using Light Emitting Diode (LED). The proposed feature selection technique used in the first aim is Neural-Discrete Hungry Roach Infestation Optimization (N-DHRIO) algorithm. The intelligent machine vision for precision irrigation system and the precision LED lighting system have successfully been developed, and it shows effective to control moisture content and light intensity of the plant precisely. In large scale plant factory, those systems can optimize plant growth and reduce the water consumption and energy costs.

Design and Implementation of LED Dimming System with Intelligent Sensor Module

An intelligent light emitting diode (LED) dimming system is designed and implemented for energy-saving lighting systems. An LED light bulb is powered by an LED driver controlled by a microcontroller using pulse width modulation (PWM) signals. By changing the duty cycle of the PWM signals, the LED driver generates a driving current of up to 1,000 mA. The current consumption by the LED light bulb exhibits a very linear characteristic that indicates that the level of LED dimming can be finely tuned. Multiple sensors-lighting intensity and ultrasonic range sensors-are combined with the LED dimming system to realize an automatically controllable LED lighting system. The light intensity sensor is capable of sensing ambient light. The ultrasonic range sensor can detect objects from 0.15 to 5.6 m at a resolution of 0.0254 m. The collected information by the light intensity and ultrasonic range sensors is processed by the microcontroller that in turn automatically controls the brightness of the LED light bulb. The algorithm of the software for the LED dimming system is also described.

Adaptive Illumination Rendering in LED Lighting Systems

We consider energy-efficiency- and user-comfort-driven design of indoor light-emitting-diode (LED) lighting control systems by achieving spatial illumination rendering adapted to presence and daylight conditions, and user preference for the amount of rendered illuminance. A localized illumination rendering strategy for lighting control is presented, where a given level of uniform illuminance is provided with a certain user satisfaction level over a user-occupied zone, and a lower illuminance level is maintained in unoccupied zones. Under these illuminance constraints, our objective is to minimize a weighted sum of power consumed in localized illumination rendering and the net user dissatisfaction with the rendered illumination. This is achieved by determining the dimming levels for controlling the multiple LED luminaires. Algorithms for centralized and distributed lighting control are proposed. Simulation results are presented to evaluate the performance of the algorithms in achieving power savings and in meeting user preferences of illumination levels.

Lumen Depreciation Diagnosis in Modulated LED Lighting Systems

Lumen depreciation is the condition that the light output of a light emitting diode (LED) lamp falls below a fraction of its peak output. In LED lighting systems with multiple LED lamps, lumen depreciation leads to undesired distortions in the rendered illumination distribution. Automatic diagnosis of lumen depreciation in LED lighting systems is thus an important problem. We propose an approach to diagnose lumen depreciation in individual LEDs using photosensors by modulating the LED lamp output with a unique identifier and encoding average drive current within, and a carrier sense multiple access on the optical channel. At the photosensor, the received signal is processed in the electrical domain. The average drive current corresponding to an individual LED lamp is extracted and a residual is computed with respect to a nominal value. A threshold detector based on testing the mean change of the residual signal is used to diagnose lumen depreciation of the LED lamps.

A New Control Method of Interleaved Single-Stage Flyback AC–DC Converter for Outdoor LED Lighting Systems

In outdoor light-emitting diode (LED) lighting systems, there are a lot of applications. Depending on the output power rating, the power stage to drive an LED can be classified into single-stage and two-stage structures. The single-stage structure is for low-power LED lighting applications. However, it is difficult to apply at over 60-70 W of output power because of its low efficiency and huge transformer at high power. On the other hand, the two-stage structure is usually used for high power applications. However, it is undesirable to cover wide output power range because of its poor power factor (PF) under the light load condition. To solve these problems, this paper proposes a new pulse duty cycle control method with pulse frequency modulation for an interleaved single-stage flyback ac-dc converter. The proposed converter provides high efficiency under heavy loads with low ac line condition and under light loads with high ac line condition. In addition, the proposed converter shows high PF and low total harmonic distortion even when the output power is very low. As a result, a single LED ac-dc converter can cover wide power range for outdoor LED lighting applications. To verify the validity of the proposed converter, an 81-W prototype converter has been implemented and experimented on.

Effects of Current Modulation Conditions on the Chromaticity of Phosphor Converted (PC) White LEDs

For two well-known modulation methods, stepwise current modulation (SCM) and pulse width modulation (PWM), the effects of driving current modulation conditions on chromaticity were experimentally investigated in a white LED lighting system. For the experimental implementation of both SCM and PWM, a white LED lighting was fabricated using phosphor converted (PC) white light emitting diodes (LEDs) and a driving circuit module was developed. By using them, the variations of illuminance, color coordinates, and spectrum were evaluated under various forward current conditions. Through the analysis in color coordinates, yellow shift in SCM and blue shift in PWM were observed on chromaticity diagrams with increasing average driving current. In addition, in order to analyze color deviation quantitatively, color distance before and after current increase, and the correlated color temperature (CCT) were calculated. As a result, for the white LED lighting in both modulation conditions, the maximum difference in the calculated CCT was obtained close to 1000 K. It means that careful consideration is required to be taken in the design of illumination systems to avoid serious problems such industrial accidents.

Energy-Saving Potential of LED Lighting Systems

Light emitting diode (LED) with its long lifetime of up 100,000 h has been receiving keen interest as there has been a rapid increase in luminous efficacy of LED recently. One interesting feature of LED is that its spectral power distributions can be easily controllable by regulating electric circuits to LED. Therefore, the same colour from LED can have quite different spectral power distribution due to metamerism. This is important as spectral power distribution is a key factor that can affect human circadian rhythm and subjective responses to changes with different spectral power distribution under the same illuminance level. The study aims to explore the energy saving potentials of LED lighting system by modulating spectral power distributions. The wavelength controllable LED system was developed in the previous study and was used in this study. Dynamic building simulations were carried out in order to quantify the total energy use including energy demands for lighting, cooling and heating indoors. Our study indicates that subjects would tend to feel brighter under red-colour emphasizing spectral power distribution, as compared to their perception under blue-colour. Also, simulation results indicate that total energy consumption can be reduced by 38% by changing spectral power distribution without sacrificing subjects’ visual comfort.

Subjective Responses to Changes in Spectral Power Distributions of LED Light

Lighting is an indispensable element in buildings, which influences visual comfort, health, well-being, work performance and building energy consumption. Light emitting diode (LED) technologies for illumination have made rapid advancements. Commercially available LED lightings have high luminous efficacies ranging from 60 to 75 lumen per watt and their spectral power distributions (SPD) are easily controllable. This study aims to reveal the potential effects of spectral power distributions of LED lighting on subjective responses including the evaluation on likeness, comfort, preference, clarity, brightness, glare, skin colour, lighting colour, overall satisfaction and work performance. Wavelength controllable LED lighting system that can render the 4324 different SPDs has been developed in this study in order to achieve the aim and 26 people participated in the experiment. The experimental results indicate that the subjective evaluation on lighting changes would depend on different SPDs under the same illuminance. The participants would tend to prefer the red-colour emphasizing SPDs with a peak wavelength of 636 nm to the blue-colour emphasizing SPDs with a peak wavelength of 453 nm. This study should contribute to reducing carbon dioxide emissions from buildings without sacrificing visual comfort and satisfaction of occupants by encouraging a wider application of LED lighting in buildings.

PLANT PRODUCTION IN A CLOSED PLANT FACTORY WITH ARTIFICIAL LIGHTING

Plant factories where leafy vegetables are cultivated until harvest in closed systems with artificial lighting were proposed, developed, and implemented in Japan during the 1980s. During the 1990s, the products from these factories received high evaluations by the food service industry, to which they primarily catered. During the 2000s, commercial production of nursery plants of fruits and vegetables was initiated in plant factories. Since the late 2000s, plant factory technology has been introduced worldwide, particularly to Asian countries. Plant factories also provide good cultivation systems for the production of medicinal plants and genetically modified crops for pharmaceutical use. In late 2000s, light-emitting diodes (LEDs) were introduced to plant factories as a more efficient light source. LEDs are expected to reduce the electricity costs of lighting and cooling because they have a higher efficiency of converting electric power to light power and exert lower cooling loads than conventional light sources. To achieve plant production in plant factories by using LEDs, more achievement of plant research is required taking engineering and plant physiological approaches, in areas such as the creation of optimal LED lighting systems, promotion of photosynthesis, control of gene expression, photomorphogenesis, and synthesis of secondary metabolites. This study reviews recent research status and achievements regarding plant production in plant factories with artificial lighting and introduces plant research topics related to LEDs utilization.

Diagnosing Lumen Depreciation in LED Lighting Systems: An Estimation Approach

Lumen depreciation, the condition that the light output falls below a fraction of its peak output, is known to be the main failure mode in light emitting diodes (LEDs). In lighting systems comprising multiple LEDs, lumen depreciation leads to reduced average illuminance and a distorted illumination rendering. Diagnosing lumen depreciation in LED lighting systems is thus an important problem. We propose an estimation approach to diagnosing individual LED failures using a photosensor system. We specifically study the impact of perturbations in the photosensor positions on diagnosability by analyzing the sensor output matrix-the matrix relating the luminous flux values of the multiple LEDs to the measurements at the photosensor system. The conditions on diagnosability are first derived in terms of bounds on the smallest singular value of the sensor output matrix. Subsequently, sufficient conditions are derived on the photosensor positions to ensure that individual LED lumen depreciations are diagnosable. Numerical results are provided to validate our analytical results.

Research and Development of LED Lighting Systems for Primary Industry(Chugoku Branch, Activating Regional Economy through Light and Lighting by Learning from the Local Pioneers)

In recent years, optical output and luminous efficacy of white Light-Emitting-Diode (LED) have rapidly been improved. It makes possible to use white LED for not only general illuminations and also special lighting equipments. In this article, application of LED lighting system for primary industry such as pest management system, crop growth control system, and fish-luring system are introduced.

Edison Revisited: Should we use DC circuits for lighting in commercial buildings?

We examine the economic feasibility of using dedicated DC circuits to operate lighting in commercial buildings. We compare light-emitting diodes (LEDs) and fluorescents that are powered by either a central DC power supply or traditional AC grid electricity, with and without solar photovoltaics (PV) and battery back-up. Using DOE performance targets for LEDs and solar PV, we find that by 2012 LEDs have the lowest levelized annualized cost (LAC). If a DC voltage standard were developed, so that each LED fixture's driver could be eliminated, LACs could decrease, on average, by 5% compared to AC LEDs with a driver in each fixture. DC circuits in grid-connected PV-powered LED lighting systems can lower the total unsubsidized capital costs by 4–21% and LACs by 2–21% compared to AC grid-connected PV LEDs. Grid-connected PV LEDs may match the LAC of grid-powered fluorescents by 2013. This outcome depends more on manufacturers' ability to produce LEDs that follow DOE's lamp production cost and efficacy targets, than on reducing power electronics costs for DC building circuits and voltage standardization. Further work is needed to better understand potential safety risks with DC distribution and to remove design, installation, permitting, and regulatory barriers.

Study of high power light emitting diode (LED) lighting system in accelerating the growth rate of Lactuca sativa for indoor cultivation

The experimental study of indoor cultivation using high power light emitting diode (LED) lighting system to accelerate the growth rate of Lactuca sativa plant is presented in this article. A novel high power LED lighting system with the use of aluminum indium gallium phosphide (AlInGaP) and indium gallium nitrate (InGaN) LEDs to produce photosynthetically active radiation (PAR) light source required for photosynthesis process of plant has been constructed. This study has verified that high power LED lighting system can accelerate the growth rate of L. sativa when compared with those plants cultivated under normal solar irradiance. Key words: Lactuca sativa, high power LED, AlInGaP, InGaN, photosynthetically active radiation, indoor plant cultivation, Solar irradiance.

Energy Saving Analysis of Solar-Powered LED Street Lighting Systems

The light emitting diode (LED) street lighting systems based on solar photovoltaic technology have been used for some time. In this paper, we present an analysis aiming at assessing the feasibility and economic performance of a solar-powered street lighting system for a 1km road. The present study introduces the architecture of a classical solar-powered LED street lighting system and estimates the total investment cost for a 1 km highway with 2 lanes. The cost comparison of solar-powered LED lighting and sodium lamps using grid was carried out. The calculations show that the energy saving effect of solar-powered LED lighting systems is obvious but the initial investment of solar-powered LED systems is more than sodium lighting systems using grid. The investment cycle is about 2.2 years under the current conditions.