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• RB LED promoted the number of shoots and leaves of in vitro Kaempferia parviflora plants, while red LED improved the length of the shoots,. • The production of photosynthetic pigments was increased under white, blue and RGB light,. • Red LED induced the accumulation of carbohydrates, while RB LED increased the production of proteins, with the highest antioxidant activity of Kaempferia parviflora observed under white LED. Black ginger (Kaempferia parviflora) is a popular plant in Thailand and Malaysia that is valued for its medicinal properties, especially its aphrodisiac qualities. Light-emitting diodes (LEDs) have successfully induced regeneration and various growth responses of black ginger plants in vitro. This study aims to investigate LED-induced photomorphogenesis of black ginger and to evaluate its physiology state. Shoot explants were grown in vitro under irradiation of white (400–750 nm), red (660 nm), blue (460 nm), RB (440 nm; 660 nm), and RGB (400 – 660 nm) to determine the vegetative responses of black ginger plants under the influence of light quality after six weeks. Biochemical analyses such as photosynthetic pigments, total carbohydrate content, protein estimation and free radical scavenging activity were also performed. The highest percentage of shoots was obtained at 96.67 % under blue light, but the maximum number of shoots and leaves were produced under RB LED with 3.21 ± 0.25 and 3.92 ± 0.28, respectively. The red light significantly promoted shoot length with an average length of 3.07 ± 0.21 cm. Rooting was spontaneously induced in all light treatments, with the highest number of roots recorded under RGB lighting at 11.80 ± 1.30. In general, RGB light significantly promoted the synthesis of photosynthetic pigments such as total chlorophyll content, carotenoids and porphyrins with 0.68 ± 0.02 µg/ml, 248.67 ± 3.38 µg/g and 3.94 ± 0.11 µg/g, respectively. The highest carbohydrate and protein contents were obtained with red and RB lights at 80.07 ± 9.15 mg/g and 309.33 ± 0.58 µg/ml, respectively. The control plants with white LED light showed the highest DPPH radical scavenging activity 94.34 ± 0.04%. Our results indicate that different light qualities induce photomorphogenesis of in vitro black ginger plants. The spectral combination with green light significantly improved the morphology and physiology of the plants. Therefore, the green spectrum should be considered as an important light source to promote plant growth in controlled environment agriculture. [ABSTRACT FROM AUTHOR]

Solar simulators are instruments used for controllable measurements of the properties of solar cells in indoor environments. The purpose of this paper is to examine the peculiarities of the photoresponses of CdTe/CdSeTe and microcrystalline Si solar cells and to reveal the pathways to reduction of spectrum mismatch effects when using light-emitting diode (LED)-based or hybrid LED and halogen lamp-based solar simulators of an A+-class spectrum with a small number of sources. While only four different LED types are needed to achieve an A+-class spectrum under updated IEC 60904-9:2020 standard requirements, as demonstrated by our results, additional ultraviolet LEDs are necessary to reduce the spectrum mismatch. For hybrid solar simulator configurations, the combination of cool white LED arrays and halogen emitters can serve as a main light source. Optimized for both solar cell types, hybrid simulators have a lower spectral deviation and better spectrum coverage compared to LED-only simulators with the same number of distinct source types. In addition, our results predict lower spectral mismatch errors for optimized simulators when compared with conventional Xe lamp-based simulators. [ABSTRACT FROM AUTHOR]

Light is a determining factor in plant morphophysiology, as it influences the growth and development of agricultural crops. Thus, the objective was to investigate the effects of light sources on the growth and development of "biquinho" pepper cultivars. The experiment was performed in two stages (Exp1 and Exp2), evaluating two cultivars (BRS Moema;Airetama biquinho) in five light sources (white LEDs, red LEDs, blue LEDs, red/blue LEDs, and fluorescent lamps). In Exp1 theplants were kept in a controlled condition, with a completely randomized design, in a 2x5 factorial scheme (cultivars x light sources) until 76 days after emergence (DAE), in which growth variables and photosynthetic pigments were evaluated. In Exp2, the plants were removed from the above conditions and transplanted in pots, being kept in greenhouse for more76 DAE. At 152 DAE, the same variables as Exp1 were evaluated, as well as gain of shoot fresh and dry mass, and gain of root fresh and dry mass. In both experiments, growth variables were affected by cultivar and the light sources, however, the behavior did not follow the same trend for all variables, indicating that the light quality influences the growthof the crops, and impacting during greenhouse conditions. [ABSTRACT FROM AUTHOR]

• The highest Fv/Fo was obtained in R LED light under foliar glycine exposure to 80 mg.l−1. • Glycine-exposed plants under light treatments exhibited higher fluorescence yield at F0, Fm, and Fv compared to normal light conditions. • Plants exposed to control light under foliar glycine treatment at 80 mg. l−1 resulted in higher Vj and Vi than those of different lighting conditions. • Under B LED light conditions, ∆b*, ∆E*, ∆C* and ∆h* were increased in comparison with normal light conditions. • Plants under B LED light upon exposure to glycine treatment at 40 mg. l−1 revealed the highest stomatal conductance. Light quality plays an important role in all growth and development stages particularly in photosynthesis properties of plant species. The light-emitting diodes (LEDs) present maximum efficiency on biological processes among artificial lighting systems. The current study was aimed to investigate different LED light color (Blue, Red and White) and glycine concentrations (0, 40 and 80 mg L−1) on photosynthetic efficiency of black henbane (Hyoscyamus niger L.) plant in a completely randomized design (CRD) with three to five replications. Results showed that the maxiumu quantum yield of PSII (0.839) was obtained in R LED light spectrum exposed plants upon glycine treatment at 80 mg. L−1, howevre, the lowest Fv/Fm (0.659) was detected in plants subjected to W LED spectrum. The highest Fv/Fo was obtained in plants grown under R LED lighting with glycine treatment at 80 mg. L−1; however, C (normal light conditions) showed the lowest Fv/Fo among the light treatments. Under B LED light conditions, ∆b*, ∆E*, ∆C* and ∆h* were increased in comparison with normal light condition. Results showed that changing trends of these traits were consistent with those of chlorophylls and carotenoids contents under different LED-based light regimes. Moreover, compared with chlorophylls content under B LED light spectrum with glycine, the carotenoids content under W LED light source was found to be a dominant pigment in black henbane plants. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are commercially used as a light source to improve plant growth and antioxidants accumulation. Growth and antioxidant system in Chinese kale microgreens illuminated with blue, red and white LEDs and sunlight, as a control, with the same duration of illumination were investigated. The red LED with low light intensity significantly enhanced hypocotyl length and fresh weight of microgreens, while blue and white LEDs and sunlight showed fairly comparable effects. The synergistic effect of blue, green and red LEDs, as white LED was the most effective in enhancing the accumulation of secondary metabolites, namely, total glucosinolates, phenolic compounds and total ascorbic acid. Microgreens grown with blue and white LEDs showed higher DPPH (1,1-diphenyl-1-picrylhydrazyl) radical scavenging activity and ferric reducing antioxidant power, whereas ABTS [2,2'-Azino-bis (3-ethylbenzothiazoline-6-sulfonic acid)] radical cation (ABTS) fared better under sunlight and blue LEDs. Overall, microgreens treated with red LED significantly reduced H2O2 and lipid peroxidation by only secondary metabolites. While blue and white LEDs treated samples utilised secondary metabolites, as well as, catalase and ascorbate peroxidase when compared to less effective superoxide dismutase in the control samples. The results suggest that light wavelength was a majority factor in enhancement antioxidant accumulation. [ABSTRACT FROM AUTHOR]

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Background: Nowadays, light-emitting diodes (LEDs) as a new lighting technology, have been emerged as an alternative source of light for plants due to their wavelength specificity, the narrow width of their bands, small size, solid structure, long lifetime, and low heat generation. Here we investigated the effect of different LED light sources on the essential oil components and antioxidant activity of Melissa officinalis. Two genotypes of lemon balm (Ilam and Isfahan) were subjected to four artificial light treatments, including white, red, blue, red + blue LEDs, and greenhouse light as natural lighting. Results: The LED lights significantly increased shoot fresh and dry weights and leaf number in the two genotypes as compared to greenhouse condition. The results showed that the content and composition of essential oil in the two genotypes were variable under different light treatments and the total amount of compounds in the Ilam genotype was higher than the other genotype. The results of analysis of the essential oil by GC/MS indicated that the highest amount of monoterpenes in the genotypes was related to citronellal under red + blue LED lamps (15.3 and 17.2% in Ilam and Isfahan genotypes, respectively) but blue, white, and greenhouse condition had the most effect on sesquiterpenes content in both genotypes. The results showed that the observed variation between the two genotypes in the essentials oil composition was related to the relative percentage of the constituents and not to the appearance or lack of a specific component. Red + blue lighting also provided the highest radical scavenging activity in both genotypes (80.77 and 82.09% for Ilam and Isfahan genotypes, respectively). Based on principal component analyses (PCA), three main groups were identified regarding genotypes and all light treatments. Conclusions: Overall, results indicated that the essentials oil composition of two genotypes of lemon balm was affected both qualitatively and quantitatively by different LED light sources; hence, LED lights might be used to improve monoterpenes, sesquiterpenes, and antioxidant activity in the selected genotypes. [ABSTRACT FROM AUTHOR]

High-power white light-emitting diodes (LEDs) have demonstrated superior efficiency and reliability compared to traditional white light sources. However, ensuring maximum performance for a prolonged lifetime use presents a significant challenge for manufacturers and end users, especially in safety–critical applications. Thus, identifying functional anomalies and predicting the remaining useful lifetime (RUL) is of enormous importance in the operational longevity of the device. To address such challenges, this study proposes a combination of distance-based Mahalanobis distance (MD), entropy generation rate (EGR), and deep learning models for improved anomaly detection and RUL prediction accuracy. Unlike conventional health indicators based on luminous flux data that are challenging to monitor relevant optical performance, the MD and EGR methods are employed to extract in-situ monitored thermal and electrical data as new health indicators. Long short-term memory recurrent neural networks (LSTM-RNN) and convolutional neural networks (CNN) are established to detect anomalies and predict the RUL. The accelerated degradation tests of 3 W high-power white LED have been conducted, and the online and offline collected experimental data are deployed for model development and performance evaluation. The performance of the proposed methods is compared against the Illuminating Engineering Society of North America (IESNA) TM-21 method. The results indicate that LSTM-RNN, when combined with either MD or EGR, can detect anomalies with significantly fewer data (70 %) than is typically required. Furthermore, a significant improvement in prediction accuracy in RUL prediction based on MD and EGR-constructed time series health indicators and employed with the LSTM-RNN model demonstrates the effectiveness of the proposed methods. [ABSTRACT FROM AUTHOR]

Light‐emitting diodes (LEDs) are among the key innovations that have revolutionized the lighting industry, due to their versatility in applications, higher reliability, longer lifetime, and higher efficiency compared with other light sources. The demand for increased lifetime and higher reliability has attracted a significant number of research studies on the prognostics and lifetime estimation of LEDs, ranging from the traditional failure data analysis to the latest degradation modeling and machine learning based approaches over the past couple of years. However, there is a lack of reviews that systematically address the currently evolving machine learning algorithms and methods for fault detection, diagnostics, and lifetime prediction of LEDs. To address those deficiencies, a review on the diagnostic and prognostic methods and algorithms based on machine learning that helps to improve system performance, reliability, and lifetime assessment of LEDs is provided. The fundamental principles, pros and cons of methods including artificial neural networks, principal component analysis, hidden Markov models, support vector machines, and Bayesian networks are presented. Finally, discussion on the prospects of the machine learning implementation from LED packages, components to system level reliability analysis, potential challenges and opportunities, and the future digital twin technology for LEDs lifetime analysis is provided. [ABSTRACT FROM AUTHOR]

Nanoplasmonics represents one of the most extensive research fields in optics on the nanoscale and has emerging applications in sensors, light-emitting devices, and photovoltaic devices. It offers a number of effects and can be combined with existing technologies by a number of approaches, the colloidal techniques representing the easiest implementation in the existing and emerging photonic components and devices. In this article, plasmonic effects are discussed in terms of three major physical phenomena (incident field enhancement, photon density of states enhancement, and nonradiative decay enhancement) in the context of various photonic processes and devices related to Raman scattering, photo- and electroluminescence, photovoltaics, photochemistry, and photodetectors. A number of instructive examples are given for metal nanospheres and nanorods showing how size, shape, core-shell design, and ambient environment can be used to get maximal use of the favorable factors while keeping unfavorable ones at reasonably safe level. A number of aspects of plasmonically enhanced secondary radiation are emphasized which have not gained close consideration to date. Among them, the following properties are discussed: the decisive role of scattering component of metal–dielectric extinction spectrum overlapping with incident and emitted/scattered light wavelength, valuable contribution to enhancement factors from spacers used to prevent emission quenching but simultaneously affecting the extinction spectrum, a pronounced dependence of enhancement factors on dielectric permittivity of the substrate, dielectric shell, and ambient medium. [ABSTRACT FROM AUTHOR]

Solar simulators replicate the spectrum of sunlight and are essential for the research, development, and quality control of photovoltaic devices. The purpose of this paper is to explore the optimization of solar simulators based on light-emitting diodes (LEDs) and hybrid LED-halogen lamp combinations in a series of simulations, by taking into account newly defined criteria of the IEC 60904-9:2020 standard: new spectral ranges, requirements for the so-called A+ class spectrum, spectral coverage, spectral deviation, and spectral mismatch factors. We reveal new ways to configure LED-based solar simulators with just four light source types to achieve A+ class spectrum. Even with A+ class spectrum significant spectral mismatch effects can remain, but may be reduced by adding or adjusting light sources. We demonstrate optimum combinations of light sources necessary for the reduction of spectral mismatch effects in the cases of crystalline silicon (c-Si) cells or both amorphous silicon (a-Si) and c-Si cells. Simulations of the current–voltage characteristics of an encapsulated aluminum back-surface field (Al-BSF) Si solar cell were performed using Synopsys TCAD (Technology Computer-Aided Design) software to reveal the expected differences of the open-circuit voltages and the short-circuit currents in a real-life operation scenario. The advantages of higher spectral coverage and more precise photogenerated current values are envisaged for hybrid solar simulators with comparable numbers of different light source types. The manufacturability of several proposed simulator designs is demonstrated by a series of proof-of-concept experiments. [Display omitted] • A+ class spectrum can be achieved with only four distinct types of light sources. • 365 nm and 1050 nm LEDs nearly eliminate spectral mismatch effects in c-Si cells. • Hybrid A+ class solar simulator of five source types with 97% spectral coverage. • Simultaneous optimization of photocurrent, spectral coverage, and spectral mismatch. [ABSTRACT FROM AUTHOR]

In order to elucidate the effect of genetic material and light source and their interaction on plant performance of potato (Solanum tuberosum L.), we studied the influence of two light sources, white fluorescent tubes (WF) and red blue LEDs with ratio 8:1 (RB) and two cultivars, 'Avanti' and 'Colomba' grown in phytotron, on growth, leaf photosynthesis and photochemistry and tuber quality. Under WF, net photosynthesis (NP) increased from the vegetative phase until flowering, then decreased during tuber bulking, with no differences between the cultivars. Lighting with RB increased the NP and the PSII maximum quantum use efficiency compared to WF. RB reduced stem elongation in both cultivars, as well as the number and area of leaves, and the aerial biomass per plant in 'Colomba', compared to WF. Conversely, tuber yield was higher in plants under RB light in both 'Avanti' and 'Colomba'. Light source did not influence the tuber content of starch and total glycoalkaloids, while it affected differently in the cultivars the protein content and the glycoalkaloid profile. Our results highlight how interactions between light source and genotype need to be considered for potato cultivation in controlled environment under artificial lighting. [ABSTRACT FROM AUTHOR]

Quantum dots (QDs) have aroused intensive research interest because of their unique optical properties and capability in the fabrication of high-performance light-emitting diodes (LEDs). However, the optical performance of the QDs is strongly affected by their intrinsic thermal sensitivity as well as the dispersion state in LEDs, thus demanding more accurate thermal control of the QDs in the LED package to promote performance optimization. In this article, a microsphere model is developed to study the thermal behavior of the QDs in the LED package by considering their monodispersion and heat accumulation. The utilization of the model provides the simulated temperature as well as the heat distribution of the QDs more in line with the experimental results, achieving an average error of only 0.01%–2%. Further study based on the microsphere model reveals that a layered package structure can offer better heat control and light uniformity for the QDs-based LEDs (QD-LEDs). The optimized package realizes a maximum of 12.5 °C temperature reduction for QDs than the conventional structure and the valid operation power for QD-LEDs to operate at 80 °C is promoted by 25%. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) are emerging lighting sources. However, it is still difficult to obtain good optical consistency of LEDs from the same batch due to phosphor sedimentation. In this paper, we introduce the centrifugation method to enhance the optical consistency of LEDs. The phosphor gradient concentration model is proposed to simulate the changes of phosphor concentration in different centrifugation time and acceleration. Moreover, the effect of these parameters on the optical performance of LEDs is discussed. The simulation results reveal that increasing centrifugal acceleration and time can enhance the optical consistency of LEDs by changing the phosphor distributions. It is suggested that the centrifugation parameters with 20 times gravitational acceleration and 6 min centrifugation time can ensure high optical consistency for LEDs, which can be taken as a reference to balance optical performance and consistency. Experimental results validate that the proposed method is beneficial to improve the optical consistency, including luminous flux and color coordinates, compared to LEDs without centrifugation. [ABSTRACT FROM AUTHOR]

Highlights • Intra-canopy illumination is implemented for bell peppers grown in passive tunnels. • Photosynthetic rates in illuminated inner-canopy leaves are enhanced by ˜4-fold. • An increase of ˜30% in the spring fruit yield is attained in illuminated plots. • The increase in yield is realized by a higher number of fruits of similar size and weight. Abstract In the past decade, light-emitting diodes (LEDs) have been replacing most other types of light sources. One emerging use for LEDs in horticulture is 'intra-canopy illumination' or 'LED-interlighting', feasible owing to their low heat output and small physical size. The interlighting technique, typically implemented in environmentally-controlled greenhouses also supplemented with overhead lighting, is mostly relevant for high-wire vegetable cultivation, in which self-shading results in light limitations for a large fraction of the canopy. Interlighting has been shown to increase the yield and/or improve fruit quality in all-year round greenhouse crops such as tomato, cucumber and sweet pepper. In this work, we utilized daytime supplemental intra-canopy LED illumination for sweet pepper grown in high-density 'Spanish' trellis systems within passive high tunnels in the Jordan Valley, Israel (latitude ˜32 °N). While canopy top at these conditions is not light-limited, extensive deep shading of the inner canopy is a disadvantage. In two experiments carried out in two separate seasons, the supplemental lighting, which enhanced the photosynthetic rates of the inner canopy foliage by 3.5- to 5.7-fold, resulted in significant increase (˜30%) of the fruit yield during the spring season. The added yield was attained by higher fruit numbers, with no notable effects on fruit size or weight. Our results raise the prospect that LED-interlighting may be a useful practical tool for maximizing fruit production, even in geographical regions of ample sunlight. [ABSTRACT FROM AUTHOR]

This paper proposes a wide-range control scheme of correlated color temperature (CCT) and illuminance of a light-emitting diode (LED) lamp, using two-component color blending. A simple control algorithm is implemented by using Grassmann's law of color mixing and McCamy's formula of CCT. Light from a white LED source is blended with that from a blue LED or a red LED to get, respectively, a CCT value higher or lower than that of the white CCT. The prototype LED lighting system can independently produce a variable CCT ranging from 2500 to 12500 K and a variable illuminance ranging from 5 to 120 lx. The algorithm is experimentally validated by hardware implementation. An empirical model to estimate the luminous parameters of the individual LED is also implemented. Experimental results show that although the system is an open-loop one, it is quite accurate with respect to set point CCT and illuminance. Despite acceptable performance in respect of these two quantities, a large deviation from the color of an ideal black body radiator is noticeable in a part of the CCT range, and a remedy of the problem has been suggested. [ABSTRACT FROM AUTHOR]

Characteristics of deep-ultraviolet (DUV) light-emitting diodes (LEDs) are investigated. DUV LEDs possess severe electron current leakage due to insufficient carrier confinement of the active region. Simply increasing the Al composition of quantum barriers (QBs) or electron-blocking layer (EBL) to enlarge the relevant potential barrier height would arise unexpected detrimental effects, such as extra polarization effect or more obstruction for hole injection. In this paper, band-engineered composition-graded QBs and EBL are proposed to resolve this issue. Simulation results show that, with appropriate designs, the leakage current of DUV LEDs could be effectively diminished with just slight side effects. [ABSTRACT FROM AUTHOR]

kAlmost all modern inorganic light-emitting diode (LED) designs are based on double heterojunctions (DHJs) whose structure and current injection principle have remained essentially unchanged for decades. Although highly efficient devices based on the DHJ design have been developed and commercialized for energy-efficient general lighting, the conventional DHJ design requires burying the active region (AR) inside a pn-junction. This has hindered the development of emitters utilizing nanostructured ARs located close to device surfaces such as nanowires or surface quantum wells. Modern DHJ III-N LEDs also exhibit resistive losses that arise from the DHJ device geometry. The recently introduced diffusion-driven charge transport (DDCT) emitter design offers a novel way to transport charge carriers to unconventionally placed ARs. In a DDCT device, the AR is located apart from the pn-junction and the charge carriers are injected into the AR by bipolar diffusion. This device design allows the integration of surface ARs to semiconductor LEDs and offers a promising method to reduce resistive losses in high power devices. In this work, we present a review of the recent progress in gallium nitride (GaN) based DDCT devices and an outlook of potential DDCT has for opto-and microelectronics. [ABSTRACT FROM AUTHOR]

Proposed is a multicomponent model for the estimation of light-emitting diode (LED) lumen maintenance using test data that were acquired in accordance with the test standards of the Illumination Engineering Society of North America, i.e., LM-80-08. Lumen maintenance data acquired with this test do not always follow exponential decay, particularly data collected in the first 1000 h or under low-stress (e.g., low temperature) conditions. This deviation from true exponential behavior makes it difficult to use the full data set in models for the estimation of lumen maintenance decay coefficient. As a result, critical information that is relevant to the early life or low-stress operation of LED light sources may be missed. We present an efficiency-decay model approach, where all lumen maintenance data can be used to provide an alternative estimate of the decay rate constant. The approach considers a combined model wherein one part describes an initial “break-in” period and another part describes the decay in lumen maintenance. During the break-in period, several mechanisms within the LED can act to produce a small (typically < 10%) increase in luminous flux. The effect of the break-in period and its longevity is more likely to be present at low-ambient temperatures and currents, where the discrepancy between a standard TM-21 approach and our proposed model is the largest. For high temperatures and currents, the difference between the estimates becomes nonsubstantial. Our approach makes use of all the collected data and avoids producing unrealistic estimates of the decay coefficient. [ABSTRACT FROM PUBLISHER]

The aim of the study was to determine the influence of the light source on the taxonomic structure and chemical composition of the harvested biomass, and on the fermentative biogas/methane production. Cultivation of a mixed microalgae culture was carried out in closed vertical photobioreactors equipped with different light sources. The effectiveness of anaerobic digestion was analysed by respirometric measurements. The harvested microalgae biomass was characterized by various taxonomic structures and varied chemical composition depending on the light source used during cultivation stage. In variants where warm white LED lighting and red light were used, species from the Cyanoprokaryota division predominated, characterized by a high concentration of organic compounds and nitrogen in the biomass. TOC values amounted to almost 430 mg/g TS. In the remaining variants, Chlorophyta predominated, and TOC values were in the range of 388.0–411.3 mg/g TS. A significantly higher biogas/methane production ( p = 0.05) was found in variants in which biomass with Cyanoprokaryota predominating was tested. The biogas yield was in the range of 383.2 L/kg VS to 400.8 L/kg VS, and the methane content was close to 55%. A lower effectiveness of biogas and methane formation were observed in variants with Chlorophyta as a predominating taxonomic group. [ABSTRACT FROM AUTHOR]

Artificial lighting is a major source of electricity demand globally. As the demand for lighting services grows over the next 40 years, especially in developing countries, efficient light-source technologies such as light-emitting diodes (LEDs) can reduce the energy consumed for lighting services and therefore its environmental impacts. LED technologies in both residential and commercial/industrial applications are expected to see dramatic improvements in luminous efficacy over the coming decades, potentially leading to more environmentally benign lighting. A scenario-based, integrated hybrid life cycle assessment quantifies and confirms the environmental benefits of deploying efficient light sources in all global regions through 2050, with electricity generation following the International Energy Agency's (IEA) BLUE Map scenario for limiting climate change to 2 degrees Celsius. Data used for previous assessments of light sources is updated and harmonized to reflect recent and expected future improvements in luminous efficacy and materials efficiency for LED lamps and luminaires. The aggregate life cycle greenhouse gas (GHG) emissions of global light provision can be reduced by more than a factor of 7 owing to decarbonization of electricity generation, increased adoption of efficient light sources, and future advances in LED technology. Estimates of the technological capability and market penetration of efficient light sources show that by 2050, a 2.5 to 2.9 times growth in the global demand for lighting services can be accommodated while still meeting IEA GHG mitigation goals and increasing metal depletion just 20% above 2010 estimates. [ABSTRACT FROM AUTHOR]

The band-engineered structure design for electron-blocking layer (EBL) and hole-blocking layer (HBL) in AlxGa1–xN-based ultraviolet light-emitting diodes (UV LEDs) is performed and analyzed theoretically. Simulation results show that the severe polarization effect is efficiently mitigated and the downward-bended band profile of the EBL is improved when the EBL is designed with a graded-composition and multiquantum barrier (GMQB) structure. As a result, the capabilities of both electron confinement and hole injection, and also the light output power are promoted. On the contrary, for the HBL, the design of composition graded and/or multiquantum barrier structures reduces the effective potential barrier height for holes in the valence band and, consequently, causes a considerable hole overflow. The UV LED, thus, exhibits superior optical performance when the LED structure is simultaneously designed with a GMQB EBL and a bulk HBL. [ABSTRACT FROM PUBLISHER]

This paper presents a scattered photon extraction (SPE) structure with a reassembled remote phosphor layer. The reassembled remote phosphor layer of the SPE structure was fabricated by combining green and red phosphor pieces with varying phosphor geometries, reducing the reabsorption of green emission by the red phosphor. The experimental results revealed that the SPE structure light-emitting diodes (LEDs) with the green and red phosphors in the remote phosphor layer demonstrated a high color rendering property. Moreover, with the same green and red phosphor weights and ratio in the remote phosphor layers, the output power and the luminous flux of the SPE structure LED with a reassembled remote phosphor layer were higher than those of SPE structure LEDs with mixed remote phosphor layers. The reduction in the reabsorption of green emission by red phosphor in the SPE structure with the reassembled remote phosphor layer was responsible for the high output power, and indicated a high correlated color temperature of the SPE structure with the reassembled remote phosphor layer. It was also found that the green emission with corresponding output power of the SPE structure LED containing the reassembled remote phosphor layer decreased with an increase in the piece number. [ABSTRACT FROM PUBLISHER]

Light-emitting diodes (LEDs) will become one of the world's most important light sources and their integration in microalgal production systems (photobioreactors) needs to be considered. LEDs can improve the quality and quantity of microalgal biomass when applied during specific growth phases. However, microalgae need a balanced mix of wavelengths for normal growth, and respond to light differently according to the pigments acquired or lost during their evolutionary history. This review highlights recently published results on the effect of LEDs on microalgal physiology and biochemistry and how this knowledge can be applied in selecting different LEDs with specific technical properties for regulating biomass production by microalgae belonging to diverse taxonomic groups. [ABSTRACT FROM AUTHOR]

A technique that saved phosphor use by 150% was applied to warm white light-emitting diodes containing composite colloidal photonic crystals (c-CPhCs) to develop an electrical source of candlelight that exhibits a high luminous flux (52 lm) and a high color-rendering index (CRI; 94). This physiologically friendly light source, which was designed to mimic the color temperature of candlelight, provides at least eight-times more luminous flux than traditional candles do. Furthermore, a UV-based adhesive curing method for enhancing the adhesion properties of c-CPhCs was also developed. A novel, inexpensive technology was implemented to produce high-CRI candlelight LEDs for use as a residential light source. [ABSTRACT FROM PUBLISHER]

In the paper, an optical design for a standard light source is proposed and demonstrated to perform high stability, high angular CCT (correlated color temperature) uniformity, and adjustable light pattern from a Lambertian-like pattern to a narrow light pattern with a full-width at half-maximum (FWHM) angle of 60 °. The optical module contains a color-mixing cylinder, a diffuser, and an absorbed cylinder. The simulation well predicts the corresponding measurements and the angular CCT deviation can be kept a certain low level, which is much lower than a general phosphor converted white LED. In addition, we apply a pcW-LED of CREE XML as the light source to the optical module to show the general adoptability of the optical module. The measurement shows that the similar behavior, with adjustable light pattern from 120 ° to 60 °. In addition, the angular correlated color temperature deviation (ACCTD) is always kept an extremely low level. [ABSTRACT FROM PUBLISHER]

A method is presented in this study to determine the junction temperature (Tj) of LED in terms of the relationship between the diode reverse current (IR) and Tj. A theoretical model for the dependence of IR on Tj is derived on the basis of the Shockley equation and is validated by our experimental results. The method is compared with the conventional forward voltage method, and its advantages have been identified. [ABSTRACT FROM AUTHOR]

This paper describes a patent-pending passive offline light-emitting diode (LED) driver that has no controlled semiconductor switches, electrolytic capacitors, auxiliary power supply, and control board. It can provide a fairly smooth current from the ac mains to drive LED strings. The new circuit has the advantages of high input power factor, high energy efficiency and luminous efficacy, long lifetime, stable luminous output, and high robustness against extreme weather conditions. In addition, over 90% of the driver material is recyclable, leading to reduction of electronic waste. It is particularly suitable public LED lighting systems, such as road lighting systems. Experimental results based on a 50-W system are included in the paper to confirm the validity of the proposal. Due to the circuit simplicity, an energy efficiency exceeding 93.6% has been achieved. [ABSTRACT FROM PUBLISHER]

In the last decades, lighting installations in plant tissue culture have generally been renewed or designed based on LED technology. Thanks to this, many different light quality advances are available but, with their massive implementation, the same issue is occurring as in the 1960s with the appearance of the Grolux (Sylvania) fluorescent tubes: there is a lack of a methodological standardization of lighting. This review analyzes the main parameters and variables that must be taken into account in the design of LED-based systems, and how these need to be described and quantified in order to homogenize and standardize the experimental conditions to obtain reproducible and comparable results and conclusions. We have designed an experimental system in which the values of the physical environment and microenvironment conditions and the behavior of plant tissue cultures maintained in cabins illuminated with two lighting designs can be compared. Grolux tubes are compared with a combination of monochromatic LED lamps calibrated to provide a spectral emission, and light irradiance values similar to those generated by the previous discharge lamps, achieving in both cases wide uniformity of radiation conditions on the shelves of the culture cabins. This study can help to understand whether it is possible to use LEDs as one standard lighting source in plant tissue culture without affecting the development of the cultures maintained with the previously regulated protocols in the different laboratories. Finally, the results presented from this caparison indicate how temperature is one of the main factors that is affected by the chosen light source. [ABSTRACT FROM AUTHOR]

This paper presents a chip-level thermal study of high-power nitride-based flip-chip (FC) light-emitting diodes (LEDs). In order to understand the thermal performance of the high-power FC LEDs thoroughly, a quantitative parametric analysis of the thermal dependence on the chip contact area, bump configuration, and bump defects was performed by finite-element-model (FEM) numerical simulation and thermal infrared (IR) microscopy testing, respectively. FEM numerical simulation results proved that the optimized bump configuration design was essential to get a uniform temperature distribution in the active layer and improve the thermal performance of the FC LED. IR microscopy testing results recognized that bump defects formed in the LED chip solder processing would lead to surface hot spots around the vicinity of these bump defects, particularly under high-current working conditions. In addition, a light-emitting dark zone was also observed in the optical field for FC LEDs with bump defects. In summary, optimized LED FC bump configuration design and good bonding quality in the chip bonding process are proved to be critical for improving the thermal performance and extending the operating longevity of high-power FC LEDs. [ABSTRACT FROM AUTHOR]

A novel gain media based on staggered InGaN quantum wells (QWs) grown by metal-organic chemical vapor deposition was demonstrated as improved active region for visible light emitters. Fermi's golden rule indicates that InGaN QW with step-function like In content in the well leads to significantly improved radiative recombination rate and optical gain due to increased electron-hole wavefunction overlap, in comparison to that of conventional InGaN QW. Spontaneous emission spectra of both conventional and staggered InGaN QW were calculated based on energy dispersion and transition matrix element obtained by 6-band k · p formalism for wurtzite semiconductor, taking into account valence-band-states mixing, strain effects, and polarization-induced electric fields. The calculated spectra for the staggered InGaN QW showed enhancement of radiative recombination rate, which is in good agreement with photoluminescence and cathodoluminescence measurements at emission wavelength regime of 425 and 500 nm. Experimental results of light-emitting diode (LED) structures utilizing staggered InGaN QW also show significant improvement in output power. Staggered InGaN QW allows polarization engineering leading to improved luminescence intensity and LED output power as a result of enhanced radiative recombination rate. [ABSTRACT FROM AUTHOR]

In a practical sense, the development of high-performance visible-spectrum light-emitting diodes (LEDs) has occurred over a period of over 60 years, beginning with the discovery of the first semiconductor p-n junction in 1940, the development of solid-state electronic band theory in the 1940s, the invention of the first bipolar transistor in 1947, and the demonstration of efficient light generation from III-V alloys in the 1950s and 1960s. This paper reviews some of the major scientific and technological developments and observations that have created the materials and device technologies currently used in the commercial mass production of high-brightness visible-spectrum LEDs and that have culminated in white-light sources exhibiting luminous efficacies of over 150 lm/W, far beyond what has been achieved with conventional lighting technologies. [ABSTRACT FROM PUBLISHER]

The infrared light emission of forward-biased silicon diodes is studied. Through ion implantation and anneal, dislocation loops were created near the diode junction. These loops suppress the light emission at the band-to-band peak around 1.1 µm. The so-called D1 line at 1.5 µm is strongly enhanced by these dislocation loops. We report a full study of photoluminescence and electroluminescence of these diodes. The results lead to new insights for the manufacturing approach of practical infrared light sources in integrated circuits. [ABSTRACT FROM AUTHOR]

Light-emitting diodes (LEDs) based on colloidal inorganic semiconductor nanocrystals (QDs) represent a completely new technology platform for the development of flat-panel displays and flat-panel lighting systems. Their major advantages are the easy tuning of the saturated color emission across the visible-NIR range and the high chemical and optical stability of the nanocrystal composites. These characteristics open the way to a new class of hybrid devices in which the low cost, flexible technology of organic LEDs is combined with the long operating lifetime of inorganic semiconductor devices. However, so far, few studies have been reported on white-LEDs based on QDs. This review shows recent developments in the general method for the fabrication of stable white-LEDs comprising QDs with a potentially long lifetime. [ABSTRACT FROM AUTHOR]

Status and future outlook of III-V compound semiconductor visible-spectrum light-emitting diodes (LEDs) are presented. Light extraction techniques are reviewed and extraction efficiencies are quantified in the 60%+ (AlGaInP) and ~80% (InGaN) regimes for state-of-the-art devices. The phosphor-based white LED concept is reviewed and recent performance discussed, showing that high-power white LEDs now approach the 100-lm/W regime. Devices employing multiple phosphors for "warm" white color temperatures (~3000-4000 K) and high color rendering (CRI>80), which provide properties critical for many illumination applications, are discussed. Recent developments in chip design, packaging, and high current performance lead to very high luminance devices (~50 Mcd/m2 white at 1 A forward current in 1times1 mm2 chip) that are suitable for application to automotive forward lighting. A prognosis for future LED performance levels is considered given further improvements in internal quantum efficiency, which to date lag achievements in light extraction efficiency for InGaN LEDs [ABSTRACT FROM PUBLISHER]

Solid-state lighting (SSL) is a pivotal emerging technology that promises to fundamentally alter and improve lighting systems-and buildings-of the future, significantly lowering energy use and costs and enhancing the quality of our building environments. No other lighting technology offers our nation so much potential to conserve electricity, at a time when our nation needs bold solutions to achieve greater energy independence. Major research and market introduction challenges must be addressed before the full promise of SSL is realized. This paper discusses the role of the U.S. Department of Energy (DOE) as a catalyst in accelerating SSL technology advances, as it works in partnership with industry, research and academic organizations, and market transformation partners. Through a series of ongoing, interactive workshops, DOE and its partners have developed an extensive plan designed to ensure that DOE funds the appropriate research and development (R&D) topics and commercialization support strategies to help our nation's best and brightest lighting experts move SSL from the laboratory into the marketplace [ABSTRACT FROM PUBLISHER]

Contemporary silicon light-emitting diodes in silicon-on-insulator (SOI) technology suffer from poor efficiency compared to their bulk-silicon counterparts. In this letter, we present a new device structure where the carrier injection takes place through silicon slabs of only a few nanometer thick. Its external quantum efficiency of 1.4 · 10-4 at room temperature, with a spectrum peaking at 1130 nm, is almost two orders higher than reported thus far on SOI. The structure diminishes the dominant role of nonradiative recombination at the n+ and p+ contacts, by confining the injected carriers in an SOI peninsula. With this approach, a compact infrared light source can be fabricated using standard semiconductor processing steps. [ABSTRACT FROM AUTHOR]

Selective activation technique was used to define a semi-insulating current-blocking layer underneath the p-pad of InGaN-GaN multiple-quantum-well light-emitting diodes (LEDs). The output power of the LEDs at 20 mA was increased 10% because less current was injected underneath the opaque p-pad. [ABSTRACT FROM AUTHOR]