LED Array Research Articles

Pathogen Growth Inhibition in Ocimum Basilicum (L.), Malus Domestica (Borkh.), and Citrus Limon (L.) by Low-Dose UV-C LED Exposure

In order to stimulate hormesis in basil, apple and lemon we used Ultraviolet C-band (UV-C) radiation emitted by an array of Light-Emitting Diodes (LEDs) at low irradiation doses followed by inoculation of the pathogens Botrytis cinerea and Penicillium digitatum. The LEDs are preferable to conventional mercury lamps when robustness and portability are required. Hormetic doses lower than those reported in the literature were used, in order to achieve short irradiation times and thus rapid treatment of crops. The results show that a dose of just 0.3 kJ m-2 released in a time interval of 3 to 14 seconds generates metabolites that inhibit, or dramatically slow, pathogen growth. After 75 days from irradiation immediately followed by inoculation, the fungal development on basil plants affected less than 30% of the epigeal part, compared to 90% in the unirradiated control. In addition, we obtained preliminary results of low-dose hormetic irradiation of lemons and apples. No fungal growth was observed in 75% of irradiated apples 15 days after irradiation and inoculation. Irradiated lemons showed complete inhibition of P. Digitatum growth. One can then infer that preventive irradiation by LED is beneficial to limit crop diseases in both pre-harvest and post-harvest without harming the plant or the environment, as a sustainable alternative to pesticides.

Dual-carrier multiplexed laser-based hybrid transmitter for high data-rate indoor optical wireless communication

In this paper we experimentally demonstrate dual-carrier modulation scheme to achieve spectrally efficient OFDM transmission in an optical wireless communication link using a hybrid laser-LED transmitter. The hybrid transmitter used in this work consists of two near infrared laser diodes at 785 nm and 808 nm used to separately modulate the real and imaginary components of the complex OFDM waveforms, collinearly combined and subsequently mixed with white LED array at a diffuser surface for indoor illumination. At the receiver end, two separate high-speed photodetectors with spectral filters are used to detect the real and imaginary components and subsequently combined to generate the complex OFDM waveforms. The optical system performance is characterized to quantify the beam spread, spot-size and spectral content of the laser beams and white LED array. The communication performance is also characterized using 16, 32, and 64-QAM/OFDM with 1, 1.25 and 1.5 Giga-samples/second sampling rates. The best communication performance with a net data-rate of 4.2 Gbps for 64-QAM/OFDM at an optimum sampling rate of 1.5 G-Samples/second is demonstrated. The dual-carrier modulation scheme studied in this work helps achieve improved spectral efficiency for OFDM transmission in an OWC link using dual transmitter-receiver pair, while at the same time requiring simplified electronic front-ends and encoding/decoding algorithms.

A 3D printed liquid metal emulsion for low stress activated stretchable electronics

A strain-induced electrically conductive liquid metal emulsion for the programmable assembly of soft conductive composites is reported. This emulsion exhibits the shear yielding and shear thinning rheology required for direct ink writing. Examples of complex self-supported 3D printed structures with spanning features are presented to demonstrate the 3D printability of this emulsion. Stretchable liquid metal composites are fabricated by integrating this emulsion into a multi-material printing process with a 3D printable elastomer. The as-printed composites exhibit a low electrical conductivity but can be transformed into highly conductive composites by a single axial strain at low stresses ([Formula: see text] 0.3 MPa), an order of magnitude lower than other mechanical sintering approaches. The effects of axial strain and cyclic loading on the electrical conductivities of these composites are characterized. The electrical conductivity increases with activation strain, with a maximum observed relaxed conductivity of 8.61 × 105 S⋅m−1, more than 300% higher than other mechanical sintering approaches. The electrical conductivity of these composites reaches a steady state for each strain after one cycle, remaining stable with low variation ([Formula: see text] standard deviation) over 1000 cycles. The strain sensitivities of these composites are quantitatively analyzed. All samples exhibit strain sensitivities that are lower than a bulk conductor throughout all strains. The printed composites showed low hysteresis at high strains, and high hysteresis at low strains, which may be influenced by the emulsion internal structure. The utility of these composites is shown by employing them as wiring into a single fabrication process for a stretchable array of LEDs.

Multiuser Massive MIMO-OFDM for Visible Light Communication Systems

Visible light communication (VLC) has emerged as a viable supplement to existing radio frequency (RF) communication systems. The limited modulation bandwidth of sources is one of the significant challenges in the multiuser (MU) VLC systems, which prohibits transmission at high data rates for each user. Since an array of LEDs is used to illuminate a room, a MU VLC system utilizing massive multiple-input multiple-output (mMIMO) orthogonal frequency-division multiplexing (OFDM) is proposed for achieving high data rates in this paper. Since the distances of the multiple transmitter-receiver links are different, their temporal delays are also different, resulting in complex channel gain and phase differences when transformed to the frequency domain in the OFDM technique. Complex channel vectors associated with different users are mutually spatially orthogonal as the number of transmitters increases. Therefore, inter-user interference (IUI) can be eliminated with simple linear signal processing, and more users can simultaneously communicate in the same time-frequency resource. In this paper, three linear precoding methods, including the maximum ratio transmission (MRT), the minimum mean square error (MMSE), and the zero-forcing (ZF), are investigated for VLC systems based on proposed MU-mMIMO-OFDM in intensity-modulation and direct-detection link. We evaluate and compare the performance of the aforementioned precoding methods in terms of the achievable spectral efficiency and total downlink optical power for different scenarios. Moreover, we derive a closed-form expression for the lower bound on the average achievable sum-rate, which we confirm the accuracy of the derived expression with the numerical simulation. The results demonstrate that the performance of the proposed method in this paper for all precoder techniques, i.e., ZF, MMSE, and MRT, is better than the previous works since the complex channel in the frequency domain is used in this paper. Furthermore, the ZF and MMSE methods are better than MRT when the ratio of the number of LEDs to the number of users is large. At the same time, when this ratio is relatively small, the MRT precoding technique outperforms the ZF and MMSE techniques.

Waving Effect Characterization for Water-to-Air Optical Wireless Communication

In this paper, we establish and experimentally verify a water-to-air (W2A) visible light communication (VLC) system through dynamic air-water interface. Considering the complexity of waves in real environments, we divide waves into largescale wave and small-scale wave. Monte Carlo simulation and experimental results show that small-scale wave mainly affects the energy distribution of the light spot on the receiving plane and the variation frequency of link gain, while largescale wave mainly affects the coverage of the light spot. In the W2A-VLC system based on light-emitting diode (LED), the statistical characteristics of variation time and link gain are mainly related to the small-scale wave, and the effect of large-scale wave can be treated as slow fading. In order to design a reliable communication system, a large-divergence-angle LED array and avalanche photodiode (APD) array are used under dynamic water surface. We investigate three cases, namely single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO). In the SIMO or MISO systems, the correlation coefficient of channel gain decreases with the inter-receiver or inter-transmitter distance. A significant transmission performance enhancement can be achieved by deploying more transmitters or receivers and increasing the distance between the transmitters or receivers. A MIMO structure can effectively increase the achievable rate. We further establish a W2A-VLC link in a deep wave pool to verify our research in the real environment. The results show that more intensive small-scale wave yields higher bit error rate (BER), and the diversity scheme can improve the transmission stability and decrease BER.

Influence of low-intensity light on the biosynthetic activity of the edible medicinal mushroom Hericium erinaceus (Bull.: Fr.) Pers. in vitro

Understanding the impact of light on the physiology and metabolism of edible and medicinal mushrooms can step up the technologies aimed at obtaining bioactive compounds. The article presents data on the influence of low-intensity quasimonochromatic light on the biosynthetic activity of Hericium erinaceus edible medicinal mushrooms in vitro. An artificial lighting setup based on light-emitting diode (LED) arrays with wavelengths ?=470 nm (blue), ?=530 nm (green), and ?=650 nm (red) was used. An argon gas laser served as a coherent visible light source at a wavelength of 488 nm. The mycelium of H. erinaceus irradiation by low-intensity light at wavelengths of 488 nm, 470 nm, and 650 nm reduced the lag phase and increased the culture?s growth rate. The highest biomass yield (12.1 g/L) on the 12th day of cultivation was achieved with light irradiation at a wavelength of 488 nm. Irradiation of the mycelium of H. erinaceus in all used wavelength ranges led to an increase in the synthesis of polysaccharides and unsaturated fatty acids. The modes of irradiation with laser light ?=488 nm and LED ?=470 nm were the most effective.

Multi-dimensional optimization for a novel photocatalytic reactor incorporating the decolorization of azo dye and thermal management of ultraviolet light-emitting diode arrays

Multi-dimensional optimization for a novel photocatalytic reactor incorporating the decolorization of azo dye and thermal management of ultraviolet light-emitting diode arrays

Light Source Homogenization Method for Large-Area LED Array Based on Microlens Array

Light Source Homogenization Method for Large-Area LED Array Based on Microlens Array

Light Sources and Irradiance Spectrum of LED solar simulator for photovoltaic devices: A Review

There is a growing demand for more applications for photovoltaic systems, which are a significant electricity source from renewable energy. Its performance test using a solar simulator is required. Light sources of solar simulator including halogen lamps and xenon lamps have been adapted to LED as a result of lamp technology. The goal of this article is to review LED solar simulator (LSS) light sources and spectrum for photovoltaic devices. Review articles from ScienceDirect and IEEE Explore from 2003 to 2022 were chosen as the basis for this analysis. The examination of spatial non-uniformity (S NE ), temporal instability, and spectral match (SM) under international standards was the result of the LSS's thorough investigation of the LED light sources design. The review discovered that LED-halogen solar simulators (LHSS) and LSS are the two main categories of solar simulator based on LED. The advantage of LHSS is that just one type of light source is required for the spectrum distribution on the infrared range. The drawback is that SM cannot be in class A. While LSS can reach class AAA and deliver good spectral coverage results in accordance with the new standard, IEC60904-9:2020, employing 10-23 LEDs of various wavelengths. The current state of LSS development is to design and build a modular LED array. S NE is still an important indicator of LSS that is reflected in the source design that is stable, economical, and sustainable. The new IEC 60904-9:2020 A+ category is discussed. The future direction of LSS for PV applications is suggested.

31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure

31.38 Gb/s GaN-based LED array visible light communication system enhanced with V-pit and sidewall quantum well structure

Three-Dimensional Measurement System of Fringe-Structured Light Based on High-Speed LED Array

Three-Dimensional Measurement System of Fringe-Structured Light Based on High-Speed LED Array

Heterocyclic amino acid molecule as a multifunctional interfacial bridge for improving the efficiency and stability of quadruple cation perovskite solar cells

Regulating the charge extraction ability of electron transport materials and constructing a chemically linked interface are imperative to enhance the power conversion efficiencies (PCEs) and improve the device stability of perovskite solar cells (PSCs). Herein, a heterocyclic amino acid molecule of 3-amino-4-pyrazolecarboxylic acid (APA) is incorporated into the SnO2/perovskite interface to improve the device performance via a multifunctional interfacial bridge. The carboxylic group and pyrazole N in APA significantly improve the optoelectronic properties of SnO2, such as carrier mobility, conductivity, energy levels and trap-state. Meanwhile, the pre-buried APA effectively passivates the buried perovskite interface, enhances the crystallinity of perovsite film and boosts the carrier extraction efficiency through chemically linking SnO2 and perovskite. As a result, the champion device delivers an impressive PCE of 24.71 % along with a fill factor of 83.56 %, which is one of the highest efficiencies for RbCsFAMA quadruple cation PSCs. Moreover, over 83 % and 80 % of their initial efficiencies are retained after 2400 h of storage and 500 h of continuous maximum output power point tracking under 1 sun illumination (white light LED array) for the unencapsulated devices, respectively. This work offers a facile approach to construct a robust interfacial bridge for efficient and stable PSCs.

Efficient Synthetic Aperture for Phaseless Fourier Ptychographic Microscopy with Hybrid Coherent and Incoherent Illumination

AbstractFourier ptychographic microscopy (FPM) is a computational high‐throughput technique for high‐resolution and wide field‐of‐view (FOV) imaging applications such as cell biology, medicine screening, and digital pathology. By integrating angle‐varied illumination, iteration phase retrieval, and synthetic aperture, it achieves a significantly enhanced imaging resolution beyond the diffraction limit of the objective lens while retaining its original large FOV without any mechanical movement. However, sufficient data redundancy is a prerequisite for the convergence of the iteration algorithm, which in turn requires dozens or even hundreds of raw images to get a decent resolution, leaving ample room for further improvement. In this paper, an efficient synthetic aperture scheme for FPM is proposed, termed ESA‐FPM. It employs both coherent and incoherent illuminations to maximize the efficiency of data utilization and achieve high spatial‐bandwidth product (SBP) reconstruction with few acquisitions. The data redundancy requirements are further analyzed, suggesting that ESA‐FPM reaches imaging resolution of using only seven images. The experiment with USAF target demonstrates that ESA‐FPM achieves theoretical resolution with only 1.6% of the data of conventional FPM. A customized miniaturized ESA‐FPM system with a high‐numerical‐aperture, low‐magnification objective lens, and a high‐brightness LED array is built, demonstrating its potential for biomedical and pathological applications.

Three-dimensional image-guided topical photodynamic therapy system with light dosimetry dynamic planning and monitoring.

Photodynamic therapy (PDT) has shown significant potential for skin disease treatment. As a key element, light is critical to influencing its treatment outcome, and light dosimetry is an issue of much concern for researchers. However, because of three-dimensional irregularity in shape and patient's movement during the therapy, irradiance hardly keeps uniform on the lesion and flux measurement remains a challenge. In this work, we report the development of a three-dimensional image-guided PDT system, and the method of dynamic irradiance planning and flux monitoring for lesions in different poses. This system comprises a three-dimensional camera for monitoring patients' movement during therapy, a computer for data analysis and processing, and a homemade LED array for forming uniform irradiance on lesions. Simulations on lesions of the face and arm show that the proposed system significantly increases effective therapy area, enhances irradiance uniformity, is able to visualize flux on the lesion, and reduces risks of burns during PDT. The developed PDT system is promising for optimizing procedures of PDT and providing better treatment outcomes by delivering controllable irradiance and flux on lesions even when a patient is moving.

Illumination system optimal design for geometry measurement of complex cutting tools in machine vision

Precision geometry measurement of complex cutting tools has a significant impact on the machinability of components in the industry. However, acquiring high-quality images in machine vision is a challenging problem due to the large slope and complex geometry. In view of the vital function of illumination, this paper proposed a method of optimal design for the LED array. First, the calculation model of irradiance distribution on the measurement plane is established, and the properties of the reflected light from the surface of cutting tools are analyzed based on the BRDF theory. Then, the optimal parameters are solved through the specific algorithm flow for the LED array design. Finally, a flexible LED light source is fabricated with the optimal parameters for different features of the cutting tools and used in the measurement. The measurement results show that the error of the optimized light source is less than 1%, and compared with the off-the-shelf light, the measurement accuracy is improved by 9.5% on average. Moreover, this method also presents the potential applied to other complex objects.

Photodynamic therapy with light-emitting diode arrays producing different light fields induces apoptosis and necrosis in gastrointestinal cancer.

Light-emitting diodes (LEDs) have become a new light source for photodynamic therapy (PDT) because of their excellent optical properties, small size, and low cost. LED arrays have so far been designed to meet the need for accurate illumination of irregular lesions. However, LED arrays determine not only the shape of the illuminated spot but also the light field, which has a significant impact on the efficacy of PDT. We designed three types of LED arrays producing different light fields, namely an intensive LED array for a uniform light field, a sparse LED array for a non-uniform light field, and a point LED array for a Gaussian-like light field, and investigated the effect and mechanism of these light fields on PDT for gastrointestinal cancer both in vitro and in vivo. We found that intensive LED-PDT induced earlier and more serious cell death, including apoptosis and necrosis, than sparse LED-PDT and point LED-PDT. Among the three LED arrays, the intensive LED array induced cells to produce more differential proteins (DEPs), mainly related to mitochondria, ribosomes, and nucleic acids. DEPs in cells subjected to sparse LED- and point LED-PDT were mainly involved in extracellular activities. For MGC-803 tumor-bearing mice, intensive LED-PDT and point LED-PDT had better tumor ablation effect than sparse LED-PDT. Notably, recurrence was observed on day 7 after sparse LED-PDT. VCAM-1 and ICAM-1 were highly expressed in sparse LEDs-PDT treated tumor tissues and were associated tumor angiogenesis, which in turn lead to poor tumor suppression. Therefore, the type of LED array significantly affected the performance of PDT for gastrointestinal cancer. Uniform light field with low power densities work better than non-uniform and Gaussian-like light fields.

Development of Driving IC for POV Display Using Two-Dimensional LED Array and Micro-LED

Development of Driving IC for POV Display Using Two-Dimensional LED Array and Micro-LED

Super multi-view near-eye display with a lightguide combiner.

We propose a lightguide-type super multi-view near-eye display that uses a digital micromirror device and a LED array. The proposed method presents three-dimensional images with a natural monocular depth cue using a compact combiner optics which consists of a thin lightguide and holographic optical elements (HOEs). Feasibility of the proposed method is verified by optical experiments which demonstrate monocular three-dimensional image presentation over a wide depth range. We also analyze the degradation of the image quality stemming from the spectral spread of the HOEs and show its reduction by a pre-compensation exploiting an adaptive moment estimation (Adam) optimizer.

Boosting electrical output of nanostructured silicon hydrovoltaic device via cobalt oxide enabled electrode surface contact

Hydrovoltaic device exploits the omnipresent water evaporation or vapor through functional materials to generate power in a facile and environmentally manner. However, overlooking of the interfacial contact between electrodes and materials is one of the dominant hindering factors in further improving the electrical outputs. Here, we report a high-efficiency silicon nanowire (SiNW) arrays-based hydrovoltaic device featuring a cobalt oxide (CoOx) layer between the top electrode and SiNWs. The CoOx layer functions as a hole-selective layer that reinforces the interfacial charge selectivity and suppresses carrier recombination. Crucially, the unique design of the CoOx-capped SiNWs architecture enables surface contact with the top electrode instead of point contact, which expands the geometric contact area and provides minimal interfacial contact resistance. Benefiting from this facile yet effective contact structure design, the device yields an open-circuit voltage of 0.83 V, a short-circuit current of 160 μA, and a maximum power density of 20 μW·cm-2 (a record among analogous devices). We also showcase that the output power of four series-connected devices viably actuates various colored light-emitting diode (LED) arrays of 25 bulbs. This finding would initiate a promising orientation toward the fabrication of high-performance hydrovoltaic devices.

Long wavelength light reduces the negative consequences of dim light at night

Many patients with autism spectrum disorders (ASD) show disturbances in their sleep/wake cycles, and they may be particularly vulnerable to the impact of circadian disruptors. We have previously shown that a 2-weeks exposure to dim light at night (DLaN) disrupts diurnal rhythms, increases repetitive behaviors and reduces social interactions in contactin-associated protein-like 2 knock out (Cntnap2 KO) mice. The deleterious effects of DLaN may be mediated by intrinsically photosensitive retinal ganglion cells (ipRGCs) expressing the photopigment melanopsin, which is maximally sensitive to blue light (480 nm). In this study, the usage of a light-emitting diode array enabled us to shift the spectral properties of the DLaN while keeping the intensity of the illumination at 10 lx. First, we confirmed that the short-wavelength enriched lighting produced strong acute suppression of locomotor activity (masking), robust light-induced phase shifts, and cFos expression in the suprachiasmatic nucleus in wild-type (WT) mice, while the long-wavelength enriched lighting evoked much weaker responses. Opn4DTA mice, lacking the melanopsin expressing ipRGCs, were resistant to DLaN effects. Importantly, shifting the DLaN stimulus to longer wavelengths mitigated the negative impact on the activity rhythms and ‘autistic’ behaviors (i.e. reciprocal social interactions, repetitive grooming) in the Cntnap2 KO as well as in WT mice. The short-, but not the long-wavelength enriched, DLaN triggered cFos expression in in the basolateral amygdala (BLA) as well as in the peri-habenula region raising that possibility that these cell populations may mediate the effects. Broadly, our findings are consistent with the recommendation that spectral properties of light at night should be considered to optimize health in neurotypical as well as vulnerable populations.