Light-emitting Diode System Research Articles

Inactivation of Hepatitis A Virus and Feline Calicivirus on Model Food Contact Surfaces by Ultraviolet Light (UV-C) Systems.

Food contact surfaces can harbor and transmit pathogens leading to outbreaks. Decontamination strategies that are user- and environmentally-friendly without toxic by-product formation are needed. Novel UV-C light-emitting diode (LED) technologies are being explored to deliver the required dose to inactivate viruses in food-processing environments. The objective of this study was to compare the effects of 279 nm UV-C LED to 254 nm UV-C against hepatitis A virus (HAV) and feline calicivirus (FCV, a cultivable human norovirus surrogate) on stainless-steel, ceramic, and glass surfaces. Viruses were surface spread on sterile stainless-steel or ceramic coupons (100 μL on 2 × 2 cm2), or glass discs (50 μL on 1 × 1 cm2), air-dried, and UV-C-treated for up to 3.75 min (surface dose = 0-49.2 mJ/cm2 for HAV and 0-24.6 mJ/cm2 for FCV). Each triplicate treatment was assayed in duplicate, and data were statistically analyzed. The D10-values for HAV treated with UV-C at 254 nm on stainless-steel, ceramic, and glass were 9.48 ± 0.34, 14.53 ± 2.52, and 6.91 ± 1.93 mJ/cm2, while with UV-C LED at 279 nm were 19.53 ± 2.45, 26.05 ± 0.60, and 8.77 ± 2.08 mJ/cm2, respectively. The D10-values for FCV treated with UV-C at 254 nm on stainless-steel, ceramic, and glass were 3.65 ± 0.06, 6.25 ± 1.90, and 4.69 ± 0.03 mJ/cm2, while with UV-C LED at 279 nm were 7.097 ± 2.11, 8.31 ± 2.12, and 7.88 ± 0.86 mJ/cm2, respectively. Higher 279 nm UV-C doses were needed to inactivate HAV and FCV compared to 254 nm UV-C on the tested surfaces. Novel UV-C LED systems using appropriate doses show promise to inactivate foodborne viruses on food contact surfaces.

Reinforcement learning control of multi-spectral LED systems for rendering optimal lighting performance in indoor environment

Light-emitting diodes (LEDs) have superseded traditional light sources due to their superior qualities. However, achieving desired spectral distribution in indoor environment still remains a challenge, particularly for optimizing multiple lighting parameters, which are nonlinear functions of the light spectra, including correlated color temperature (CCT), color rendering index (CRI) and circadian action factor (CAF). Existing studies have been mainly devoted to seeking optimal solutions, by means of various optimization methods, e.g. genetic algorithms. However, these methods can only result in fixed recipes to achieve pre-assigned reference parameters, and cannot meet the need of dynamic varying lighting environment. Therefore, this paper proposes a novel framework for optimal spectrum design and control in multichannel LED lighting systems. It surpasses traditional methods by employing reinforcement learning (RL) to generate an entire optimal spectral power distribution (SPD) model, comprehensively considering CCT, CRI, CAF, and other relevant parameters. This framework integrates the RL-based optimal SPD generator with a corresponding real-time controller, bridging the gap between simulations and real-world applications. The effectiveness of this new framework has been verified by an experimental prototype, showcasing both the optimal SPD and the achieved control performance. This work paves the way for high-quality, user-centric lighting with dynamic CCT and spectral control, and enables the creation of lighting environments that optimize human well-being, productivity, and overall experience.

Essential oil constituents and secondary metabolites of Mentha viridis under tissue culture technique using violet visible light emitting diodes (LEDs)

This study aimed to propagate the valuable medicinal plant Mentha viridis through in vitro culture of nodal segments measuring approximately 1-1.5 cm. Two different types of light-emitting diode (LED) systems were used to apply three different concentrations of two different cytokinins: 6-benzylaminopurine (BAP) and thidiazuron (TDZ) at 0, 1, or 2 mg/L. The LED systems were white as a control and violet, which is a 1:1 ratio of red and blue light. After a 30-day incubation period, the results revealed significant improvements in the survival rate and the number of shoots per explant across the various treatment groups. With MS medium supplemented with 2 mg/L TDZ and illuminated by white and violet LEDs, the highest values were obtained, yielding survival rates of 93.3% and 13.3 shoots per explant, respectively. Moreover, the treatment involving 2 mg/L TDZ under violet LEDs illumination exhibited superior outcomes in terms of leaf count per explant, callus formation, and callus size. Notably, no callus formation was observed in response to BAP treatments. All treatments resulted in a significant increase in antioxidant enzyme activity and the accumulation of various compounds, such as anthocyanin, ascorbic acid, phenols, flavonoids, peroxidase, and polyphenol oxidase, when compared to the control in a broader context, the levels of IAA, kinetin, and zeatin increased, while GA3 and ABA decreased in response to the applied treatments, as compared to the control. Additionally, ten compounds were consistently found in all treatments by GC/MS analysis of the micro-propagated Mentha, with carvone accounting for the highest proportion (43.5%) and being the predominant component. Among all treatments, nodal segments that were exposed to violet LEDs and grown on MS medium supplemented with 1 mg/L TDZ had the highest carvone content.

A metal-free Z-scheme PPy/MCN heterojunction for antibiotic removal via synergism of photocatalysis and peroxymonosulfate activation

Developing an active and synergistic system based on photocatalysis and peroxymonosulfate (PMS) activation is considered an effective strategy for efficient removal of antibiotics. However, photocatalytic heterojunctions generally comprise metallic catalysts that can cause metal leaching and secondary pollution, and a clear understanding of the synergy between photocatalysis and PMS activation is still missing. Herein, a metal-free Z-scheme polypyrrole (PPy)/melamine-derived graphitic carbon nitride (MCN) heterojunction photocatalyst was synthesized via calcination and in-situ loading for catalyzing the degradation of ciprofloxacin (CIP) and other emerging pollutants in a visible light-emitting diode (LED)/PMS synergistic system, which showed a significantly higher activity than the single LED and PMS systems. The optimal 0.5 %PPy/MCN (0.5 % is the mass ratio of PPy in the mixture of PPy/MCN) performed well under a wide pH range (3–11), while exhibiting superior anti-interference for common water constituents and outstanding reusability and stability. The 0.5 %PPy/MCN/LED/PMS synergistic system showed the highest kinetic constant (0.0643 1/min), which increased 3.00, 6.77 and 2.91-fold over the 0.5 %PPy/MCN/PMS, 0.5 %PPy/MCN/LED, and MCN/LED/PMS system, respectively. Mechanistic investigation and theoretical calculations revealed that PPy, with its high conductivity and strong light absorption ability, facilitated the generation and separation of e−/h+ in the 0.5 %PPy/MCN/LED/PMS system and activated PMS for generating reactive species such as 1O2, which degraded cCIP together with h+. Furthermore, electron transfer pathway (ETP) was elucidated using electrochemical characterizations. CIP was degraded via ring opening, cleavage hydroxylation, ammonia oxidation and elimination reactions, which substantially reduced the toxicity of CIP. Overall, this study may help the rational design of metal-free catalysts and provide a deep insight for the LED/PMS synergistic mechanisms.

Automatic Photo-Cross-Linking System for Robotic-Based In Situ Bioprinting.

This work reports the design and validation of an innovative automatic photo-cross-linking device for robotic-based in situ bioprinting. Photo-cross-linking is the most promising polymerization technique when considering biomaterial deposition directly inside a physiological environment, typical of the in situ bioprinting approach. The photo-cross-linking device was designed for the IMAGObot platform, a 5-degree-of-freedom robot re-engineered for in situ bioprinting applications. The system consists of a syringe pump extrusion module equipped with eight light-emitting diodes (LEDs) with a 405 nm wavelength. The hardware and software of the robot were purposely designed to manage the LEDs switching on and off during printing. To minimize the light exposure of the needle, thus avoiding its clogging, only the LEDs opposite the printing direction are switched on to irradiate the newly deposited filament. Moreover, the LED system can be adjusted in height to modulate substrate exposure. Different scaffolds were bioprinted using a GelMA-based hydrogel, varying the printing speed and light distance from the bed, and were characterized in terms of swelling and mechanical properties, proving the robustness of the photo-cross-linking system in various configurations. The system was finally validated onto anthropomorphic phantoms (i.e., a human humerus head and a human hand with defects) featuring complex nonplanar surfaces. The designed system was successfully used to fill these anatomical defects, thus resulting in a promising solution for in situ bioprinting applications.

Design and Development of an Efficient, High Power Factor, Low-Cost, RGB LED System for Tuneable Lighting Application

Branded smart red (R) – green (G) – blue (B) light emitting diode (LED) products commercially available in developing countries are too costly to afford for most of the population, especially for household applications. Locally manufactured cheaper alternatives of such products suffer from poor power factor and reduced circuit efficiency. To address these technical issues, a smart RGB LED system is presented here which offers high input power factor, good circuit efficiency, and at the same time lower fabrication cost and user-friendly control interface. The unique features of the proposed system are the front-end AC/DC converter is a constant-voltage, multiple-output flyback converter that mitigates the need of multiple drivers and inductors. The second is that the same converter is operated in discontinuous conduction mode to achieve a high input power factor. The third is that for dimming and colour tuning, pulse width modulation (PWM) control of the MOSFET switches is accomplished by an Arduino Mega 2560 microcontroller instead of other costlier and more sophisticated options. And the fourth is that the microcontroller gets its command signal from a smartphone or computer through an HC‑05 Bluetooth module. Through laboratory testing, it is confirmed that the LED system offers close-to-unity input power factor (0.928–0.985) and high efficiency of (88.14–95.46) % for a wide range of colour and luminous intensity. A comparative study reveals that the developed system is a better option than the earlier reported prototypes of multicolour LED systems in terms of the bill of material, economy, power factor, and efficiency.

Characterization of ink-based phantoms with deep networks and photoacoustic method

<p class="abstract">This study aims to explore the feasibility of using an in-house developed photoacoustic (PA) system for predicting blood phantom concentrations using a pretrained Alexnet and a Long Short-Term Memory (LSTM) network. In two separate experiments, we investigate the performance of our strategy using a point laser source and a color-tunable Light-Emitting Diode (LED) as the illumination source. A single-point transducer is employed to measure signal change by adding ten different black ink concentrations into a tube. These PA signals are used for training and testing the employed deep networks. We found that the LED system with light wavelength of 450 nm gives the best characterization performance. The classification accuracy of the Alexnet and LSTM models tested on this dataset shows an average value of 94% and 96%, respectively, making this a preferred light wavelength for future operation. Our system may be used for the noninvasive assessment of microcirculatory changes in humans.</p>

APPLICATION OF ULTRAVIOLET LED SYSTEMS IN THE GRAIN PROCESSING AND COMPOUND FEED INDUSTRIES

The materials of the article outline the features of the use of ultraviolet LED systems in industry, and propose a solution for their use in the grain processing and compound feed industry. Ultraviolet light (UV) is a well-researched and widely used means of decontamination and disinfection of surfaces, air, water, and food. Usually, far ultraviolet radiation (or ultraviolet C, UVC) with a wavelength of 254 nm is used, which corresponds to the peak absorption of wave energy by the DNA of a living cell. There is a mathematical mechanism for calculating the parameters of radiation in relation to its effect on microorganisms: a curve describing the microbial death depending on the increase in the radiation dose received by the bacteria and formulae for the relationship between the three main parameters (dose, radiation flux and exposure duration). Ultraviolet lamps (tubes) are commonly used, on the basis of which a large number of emitters have been developed for different needs. There are also emitters for grain and feed disinfection in use, but only outside of industrial production lines. Ultraviolet irradiation is not used directly on manufacturing lines so far. However, it can be used to reduce the microbial burden of a feed or food product prior to packaging the finished product. For this purpose, ultraviolet light-emitting diodes (LEDs) available on the world market today can be used. However, their use faces difficulties: ultraviolet LEDs emit wavelengths longer than lamps (at about 275 nm or more), which requires an increase in the duration of irradiation, which is undesirable for industrial processing of products directly on the line. However, the small size of the UVC LEDs will allow them to be installed in grain processing and feed mills inside equipment (magnetic separators, gravity feeders, etc.) with appropriate protection against damage by moving material. In addition, suspended emitters of any configuration can be placed above belt conveyors that move material at a certain speed. This approach will require certain measures to control the efficiency of irradiation (requires microbiological studies) and to protect personnel from the harmful effects of ultraviolet rays (means of personal and collective protection, measurement of radiation intensity).

Modeling of Hybrid Henry Gas Solubility Optimization Algorithm with Deep Learning-Based LED Driver System

Light emitting diodes (LEDs) have become an effective lighting solution because of the characteristics of energy efficiency, flexible controllability and extended lifetime. They find use in numerous lighting systems for residents, industries, enterprises and street lighting applications. The efficiency and trustworthiness of the LED systems considerably based on the thermal mechanical loading improved several degradation schemes and respective interfaces. The complication of the LED systems limits the theoretic interpretation of the core reasons for the luminous variation or the formation of the direct correlation among the thermal aging loading and the luminous output. Therefore, this paper designs a new hybrid Henry gas solubility optimization with deep learning (HHGSO-DL) algorithm for LED driver system design. The presented HHGSO-DL technique mainly concentrates on the derivation of empirical relationships among the design parameters, thermal aging loading and luminous outcomes of the LED product. In the presented HHGSO-DL technique, bidirectional long short-term memory (BiLSTM) algorithm is executed for examining the empirical relationship and its hyperparameters can be tuned by the HHGSO algorithm. In this work, the HHGSO algorithm is derived by the integration of traditional HGSO algorithm with oppositional-based learning (OBL) concept. The performance of the HHGSO-DL technique can be investigated on LED chip packaging and LED luminaire with thermal aging loading. The extensive results demonstrate the promising performance of the HHGSO-DL technique over other state-of-the-art approaches.

Improved disinfection performance for 280 nm LEDs over 254 nm low-pressure UV lamps in community wastewater

Ultraviolet (UV) disinfection has been incorporated into both drinking water and wastewater treatment processes for several decades; however, it comes with negative environmental consequences such as high energy demands and the use of mercury. Understanding how to scale and build climate responsive technologies is key in fulfilling the intersection of UN Sustainable Development Goals 6 and 13. One technology that addresses the drawbacks of conventional wastewater UV disinfection systems, while providing a climate responsive solution, is UV light emitting diodes (LEDs). The objective of this study was to compare performance of bench-scale 280 nm UV LEDs to bench-scale low pressure (LP) lamps and full-scale UV treated wastewater samples. Results from the study demonstrated that the UV LED system provides a robust treatment that outperformed LP systems at the bench-scale. A comparison of relative energy consumptions of the UV LED system at 20 mJ cm−2 and LP system at 30 and 40 mJ cm−2 was completed. Based on current projections for wall plug efficiencies (WPE) of UV LED it is expected that the energy consumption of LED reactors will be on par or lower compared to the LP systems by 2025. This study determined that, at a WPE of 20%, the equivalent UV LED system would lead to a 24.6% and 43.4% reduction in power consumption for the 30 and 40 mJ cm−2 scenarios, respectively.

Development and optimization of LED systems for surface fungal decontamination of fresh produce

Uneven irradiation is the major challenge of light-emitting diode (LED) antimicrobial technology. This study developed different LED illumination systems with multi-directional light sources, spotlight reflector (SR), and parabolic reflector (PR) to ensure the high antifungal efficiency of LED on artificially inoculated litchi fruit. Results showed that multi-light LEDs enable multi-angle irradiation, therefore, could reach higher inactivation rates under the comparable energy output. Integrating LED with SR could gather the scattering light and improve the inactivation efficiency (LEDs < LEDs + SR). The addition of PR enhanced bottom irradiation, leading to a comparable effect with an extra light source (LED + SR + PR = dual-LEDs). Moreover, when comparing the energy consumption required for 90 % inactivation of fungi, the LED systems combined SR and/or PR required less power consumption than those of LEDs alone. The antifungal effects of developed systems were further validated by natural samples. These results suggest several feasible solutions to improve the antifungal efficiency of LED and also provide practical system designs to broaden the LED application in the food industry.

Dual red and near-infrared light-emitting diode irradiation ameliorates LPS-induced otitis media in a rat model.

Objective: Otitis media (OM) is an infectious and inflammatory disease of the middle ear (ME) that often recurs and requires long-term antibiotic treatment. Light emitting diode (LED)-based devices have shown therapeutic efficacy in reducing inflammation. This study aimed to investigate the anti-inflammatory effects of red and near-infrared (NIR) LED irradiation on lipopolysaccharide (LPS)-induced OM in rats, human middle ear epithelial cells (HMEECs), and murine macrophage cells (RAW 264.7). Methods: An animal model was established by LPS injection (2.0mg/mL) into the ME of rats via the tympanic membrane. A red/NIR LED system was used to irradiate the rats (655/842nm, intensity: 102mW/m2, time: 30min/day for 3 days and cells (653/842nm, intensity: 49.4mW/m2, time: 3h) after LPS exposure. Hematoxylin and eosin staining was performed to examine pathomorphological changes in the tympanic cavity of the ME of the rats. Enzyme-linked immunosorbent assay, immunoblotting, and RT-qPCR analyses were used to determine the mRNA and protein expression levels of interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α (TNF-α). Mitogen-activated protein kinases (MAPKs) signaling was examined to elucidate the molecular mechanism underlying the reduction of LPS-induced pro-inflammatory cytokines following LED irradiation. Results: The ME mucosal thickness and inflammatory cell deposits were increased by LPS injection, which were reduced by LED irradiation. The protein expression levels of IL-1β, IL-6, and TNF-α were significantly reduced in the LED-irradiated OM group. LED irradiation strongly inhibited the production of LPS-stimulated IL-1β, IL-6, and TNF-α in HMEECs and RAW 264.7 cells without cytotoxicity in vitro. Furthermore, the phosphorylation of ERK, p38, and JNK was inhibited by LED irradiation. Conclusion: This study demonstrated that red/NIR LED irradiation effectively suppressed inflammation caused by OM. Moreover, red/NIR LED irradiation reduced pro-inflammatory cytokine production in HMEECs and RAW 264.7 cells through the blockade of MAPK signaling.

Effect of germicidal short wavelength ultraviolet light on the polyphenols, vitamins, and microbial inactivation in a highly opaque apple juice

AbstractThe aim of this investigation was to study the efficacy of UV‐C light emitting diode (LED) system operating at 263 nm for the inactivation of Listeria monocytogenes and Escherichia coli O157:H7. UV‐C irradiation was applied to stirred 5 ml samples, using a collimated beam LED system operating at a 263 nm wavelength. UV irradiation doses ranging from 0 to 160 mJ/cm2 were also delivered to apple juice (AJ) and polyphenols and vitamins were profiled. Liquid chromatography–mass spectrometry (LC–MS/MS) analysis was conducted to assess the stability of polyphenols or vitamins in UV‐C exposed AJ. The polyphenol and vitamin results demonstrated that UV‐C irradiation in AJs at relevant commercial UV doses induced significant reductions in the concentrations of selected polyphenols and vitamins, p &lt; .05. Ascorbic acid was reduced to 32%, at 160 mJ/cm2 whereas 17% reduction was observed at 40 mJ/cm2. Riboflavin was observed to be relatively stable. Epicatechin and chlorogenic were significantly reduced at high exposure doses. In contrast, minor changes were observed at 40 mJ/cm2. Results show that UV‐C irradiation effectively inactivated pathogenic microbes in AJ. Inactivation levels of all organisms were proportional to UV‐C dose. The log reduction kinetics of microorganisms followed log‐linear and with higher R2 (&gt;0.95). The decimal reduction dose (D10) values of 4.16 and 3.84 mJ/cm2 were obtained from the inactivation of E. coli and L. monocytogenes in AJ. The results from this study imply that adequate log reduction of pathogens is achievable in AJ and suggests significant potential for UV‐C treatment of other opaque liquid foods.

LED Systems Applications and LED Driver Topologies: A Review

High-power light-emitting diodes (LEDs) and high-brightness LEDs have revolutionized the lighting industry. The availability of cost-effective LEDs with high luminous flux, efficacy, and reliability has expanded their application to replace incandescent and fluorescent light sources. They have also enabled many new applications that were considered infeasible before, due to the inherent limitations of traditional sources of light. This survey provides a comprehensive overview of ac- and dc-supplied LED lighting systems and their applications, corresponding specifications and their similarities to/differences from regular power supplies. Restrictions imposed by LEDs characteristics, safety considerations, and dimmers are discussed. Also, LED driving approaches are categorized and their suitability for different applications is provided.

An Integrated Circuit Based, Single-Inductor-Dual-Output Buck LED Driver for Dimmable and Color Temperature Tunable Indoor Lighting Application

Tunability of correlated color temperature (CCT) and dimmability are the two major sought after features of functional solid-state lighting. This paper presents a low-cost, efficient, single-inductor-dual-output buck driver that facilitates CCT-control and dimming of a light emitting diode (LED) module composed of cool-white and warm-white chips. The proposed driver is designed based on two familiar integrated circuits (ICs), namely LM2596 and NE556. LM2596 serves as the main switching regulator and amplitude modulation (AM) controller whereas NE556 serves as the constant-frequency, dual-output pulse-width-modulation (PWM) controller. The exponential model of LED is exploited for improved estimation of the design parameters of the LED module and the driver circuit. The developed driver prototype is tested for its electrical, photometric, and colorimetric performances. The driver offers a full-load efficiency of about 90% for a 12-W test LED module. Under different operating modes, the LED system can produce warm, cool, or neutral white light and at the same time, the produced illuminance can be varied over a wide range. Moreover, the light flicker is imperceptible since the PWM frequency is set according to IEEE-1789 guideline.

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.

Thermal Effect of Cylindrical Heat Sink on Heat Management in LED Applications

Light Emitting Diode (LED) applications are increasingly used in various microelectronic devices due to their efficient light generation. The miniaturisation of the LED and its integration into compact devices within the weight limit have resulted in excessive heat generation, and inefficient management of this heat could lead to the failure of the entire system. Passive and/or active heat sinks are used for dissipating heat from the system to the environment to improve performance. An ANSYS design modeller and transient thermal conditions were utilised in this study to design and simulate the LED system. The modeller performs its function by utilising the Finite Element Method (FEM) technique. The LED system considered in this work consists of a chip, thermal interface material, and a cylindrical heat sink. The thickness of the Cylindrical Heat Sink (CHS) fins used in the investigation is between 2 mm and 6 mm, whilst ensuring the mass of heat sinks is not more than 100 g. The input power of the LED chip is between 4.55 W and 25.75 W, as required by some original equipment manufacturers (OEMs). A mesh dependency study was carried out to ensure the results were synonymous with what can be obtained practically. The simulation results suggest that the power ratings did not affect the thermal resistance of the CHS. In addition, the thermal resistance increased with the increased thickness of the CHS fin. The efficiencies of the heat sink were found to increase with an increased thickness of the cylindrical fin and the accuracy between the calculated and simulated thermal efficiency ranges from 84.33% to 98.80%. Evidently, the CHS fin of 6 mm thickness is more efficient than the other CHS fins, as depicted in this study.

Rapid calculation method to evaluate thermal management of LED systems based on an improved multi-layer model

An improved laminated structure model of LED systems is proposed. Besides the light-emitting diode (LED) chip, printed circuit board (PCB) substrate, heat sink, etc, additional interface layers are applied to model the non-ideal surface of thermal interface materials (TIMs). And a rapid calculation method is developed for temperature-related calculations. Through comparisons, the method is proved to be valid, and the execution time can be greatly reduced. It is found that the air gap at the TIM surface does hinder heat conduction but the effect is not obvious. The influence of LED chips on system thermal management is comprehensively analyzed. For a single LED chip, the junction temperature shows a linear relationship with its thermal resistance and heat power. The chip size, as well as the aspect ratio between the chip and the PCB substrate, has great effects on the junction temperature. For a multi-chip array, the impact of the chip quantity is suggested to be considered combined with the chip layout. The mutual thermal interaction among LED chips is of most concern, which will become more serious with an increasing number of chips. The work provides a rapid and flexible evaluation method for thermal management of LED systems.

Bayesian Hierarchical Modelling for Uncertainty Quantification in Operational Thermal Resistance of LED Systems

Remaining useful life (RUL) prediction is central to prognostics and reliability assessment of light-emitting diode (LED) systems. Their unknown long-term service life remaining when subject to specific operating conditions is affected by various sources of uncertainty stemming from production of individual system components, application of the whole system, measurement and operation. To enhance the reliability of model-based predictions, it is essential to account for all of these uncertainties in a systematic manner. This paper proposes a Bayesian hierarchical modelling framework for inverse uncertainty quantification (UQ) in LED operation under thermal loading. The main focus is on the LED systems’ operational thermal resistances, which are subject to system and application variability. Posterior inference is based on a Markov chain Monte Carlo (MCMC) sampling scheme using the Metropolis–Hastings (MH) algorithm. Performance of the method is investigated for simulated data, which allow to focus on different UQ aspects in applications. Findings from an application scenario in which the impact of disregarded uncertainty on RUL prediction is discussed highlight the need for a comprehensive UQ to allow for reliable predictions.

Enhancement of photosynthesis efficiency and yield of strawberry (Fragaria ananassa Duch.) plants via LED systems

Due to advances in the industrial development of light-emitting diodes (LEDs), much research has been conducted in recent years to get a better understanding of how plants respond to these light sources. This study investigated the effects of different LED-based light regimes on strawberry plant development and performance. The photosynthetic pigment content, biochemical constituents, and growth characteristics of strawberry plants were investigated using a combination of different light intensities (150, 200, and 250 μmol m−2 s−1), qualities (red, green, and blue LEDs), and photoperiods (14/10 h, 16/8 h, and 12/12 h light/dark cycles) compared to the same treatment with white fluorescent light. Plant height, root length, shoot fresh and dry weight, chlorophyll a, total chlorophyll/carotenoid content, and most plant yield parameters were highest when illuminated with LM7 [intensity (250 μmol m−2 s−1) + quality (70% red/30% blue LED light combination) + photoperiod (16/8 h light/dark cycles)]. The best results for the effective quantum yield of PSII photochemistry Y(II), photochemical quenching coefficient (qP), and electron transport ratio (ETR) were obtained with LM8 illumination [intensity (250 μmol m−2 s−1) + quality (50% red/20% green/30% blue LED light combination) + photoperiod (12 h/12 h light/dark cycles)]. We conclude that strawberry plants require prolonged and high light intensities with a high red-light component for maximum performance and biomass production.