Light-emitting Diode Lamps Research Articles

In Situ Fabrication of Mn‐Doped 2D Perovskite‐Polymer Phosphor Films with Green‐Red Dual Emissions for Yellow Lighting

Abstract2D metal halide perovskites have emerged as highly bright and stable light emitters, which can be employed as phosphors for optically pumped luminescence devices. However, the intrinsic volatile property is the main weakness to achieve their long‐term lighting applications. Here, an in situ doctor blade method is developed to fabricate a flexible large‐area (20 × 25 cm2) PEA2PbI4:2Mn‐PVDF film with green‐red dual emissions. Under UV light‐emitting diode (LED) excitation, this yellow phosphor device shows a maximum luminance value of 250 cd m−2, an extremely large full width at half maximum of 189 nm, and a color coordinate of (0.47, 0.50). The device can pass 120 h of water soaking and 85 °C/85% relative humidity of harsh environment tests, which benefit from the strong interaction of 2D perovskite and hydrophobic PVDF polymer. Different from electroluminescence yellow LED devices, Mn‐doped 2D perovskite‐polymer phosphor films excited by UV LED and fluorescent lamp provide an opportunity to achieve low‐cost indoor yellow lighting in some UV‐sensitive places.

Efficacy of 265-nm ultraviolet light in inactivating infectious SARS-CoV-2

Although, Low-pressure (LP) mercury lamps that emit wavelengths of around 254 nm have been widely applied as ultraviolet (UV) light devices for decontamination of microorganisms, they have raised environmental concerns due to their mercury content. Therefore, UV-LED lamps have high potential for practical use as a replacement for LP mercury lamps. In this study, we evaluated the efficacy of 265-nm UV irradiation in comparison to 254-nm and 280-nm UV irradiation for inactivating infectious severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Irradiation from a 265-nm deep UV light-emitting diode (DUV-LED) lamp efficiently inactivated SARS-CoV-2 at a similar level as a 254-nm UV cold cathode lamp, and at a higher level than a 280-nm DUV-LED lamp.

Working environment of tritium analysis for photoluminescence control

The conventional tritium analysis process using a liquid scintillation counter (LSC) requires over 24 h of waiting time to reduce the interference from the luminescence of the sample cocktail. The working efficiency of tritium measurement using an LSC worsens as the waiting time for luminescence decay increases. We hypothesize that this waiting time can be shortened by using light-emitting diode (LED) lamps as lighting equipment in a measurement laboratory because the emission spectra of some LED lamps contain no ultraviolet rays. Thus, a sample cocktail was prepared under an LED lamp. The count rate of this cocktail was reduced to the background of the LSC (ca. 3 cpm) within several hours. By contrast, the luminescence of a cocktail placed under daylight took approximately 100 h to decay. Therefore, the use of LED lamps is effective for luminescence control and shortening the waiting time in a measurement process.

Smartphone-based technique for the determination of a titration equivalence point from an RGB linear-segment curve with an example application to miniaturized titration of sodium chloride injections

A smartphone-based technique for determining the titration equivalence point from a linear-segment curve was developed for the first time. In this method, a titrant in an increasing microliter-volume was added to a set of sample aliquots containing an indicator covering both sides of the equivalence point. The solutions were subsequently photographed in one shot, in a dark box using a smartphone camera and an illuminating screen of a tablet or light emitting diode lamps arranged below a white acrylic sheet as a light source. After the colors of the solutions were delineated to Red, Green, and Blue (RGB) values, 1/log G was used to construct a plot in which the equivalence point was located at the intersection of the two lines in the region before and after the equivalence point. The technique was successfully applied to the miniaturized titration of sodium chloride injections, showing the good linear relationship of equivalence points to the sodium chloride concentration in the range of 0.4163–0.9675% w/v (R2 of 0.9998). The assay was accurate (% recovery of 98.92–100.52), precise (% relative standard deviation ≤ 1.20), and unaffected by the use of different types of microplates, smartphones, and RGB analysis tools. Additionally, it required no expensive nor complicated equipment and offered the possibility of performing analysis on a single smartphone device when it was used with a mobile application developed to aid data processing and immediate production of reports of analytical results.

LED light sources improved the essential oil components and antioxidant activity of two genotypes of lemon balm (Melissa officinalis L.)

BackgroundNowadays, 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.ResultsThe 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.ConclusionsOverall, 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.

A multiwavelength model to improve microalgal productivity and energetic conversion in a red-blue light emitting diodes (LEDs) continuous photobioreactor

Irradiation with light emitting diodes (LEDs) is proposed as a method to increase the photoconversion efficiency in large-scale microalgal cultivation. Although several authors have reported the possibility of using colored LEDs in batch systems and for many species, the overall energy efficiency of a continuous system integrated with fine-tuned LED technology is still not available. In this work, the cyanobacterium Arthrospira maxima was cultivated under a R/B (red/blue) LED lamp at increasing light intensities, in order to study the effects of light quality on microalgal performances. Kinetic growth parameters were retrieved from respirometric tests and implemented in a mathematical model to examine the effects of process variables on microalgal growth and to predict maximum biomass productivity in the multi-wavelength spectrum employed, which was also included in the simulation tool. The efficiency of both photosynthetic and LEDs were examined for energy evaluation. It was found that integrating tailored LEDs in microalgal cultivation increases process efficiency by reducing light energy waste. Moreover, integrating tailored LEDs was also found to be more efficient than white LED source, due to their higher energetic efficiency.

Photodegradation of reactive blue 19 dye using magnetic nanophotocatalyst α-Fe2O3/WO3: A comparison study of α-Fe2O3/WO3 and WO3/NaOH

The photocatalytic degradation of reactive blue 19 (RB19) dye was investigated in a slurry system using ultraviolet (UV) and light-emitting diode (LED) lamps as light sources and using magnetic tungsten trioxide nanophotocatalysts (α-Fe2O3/WO3 and WO3/NaOH) as photocatalysts. The effects of different parameters including irradiation time, initial concentration of RB19, nanophotocatalyst dosage, and pH were examined. The magnetic nanophotocatalysts were also characterized with different methods including scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), photoluminescence (PL), differential reflectance spectroscopy (DRS), Fourier transform infrared spectroscopy (FTIR), and vibrating sample magnetometry (VSM). The XRD and FTIR analyses confirmed the presence of tungsten trioxide on the iron oxide nanoparticles. The VSM analysis confirmed the magnetic ability of the new synthesized nanophotocatalyst α-Fe2O3/WO3 with 39.6 emu/g of saturation magnetization. The reactor performance showed considerable improvement in the α-Fe2O3-modified nanophotocatalyst. The impact of visible light was specifically investigated, and it was compared with UV-C light under the same experimental conditions. The reusability of the magnetic nanophotocatalyst α-Fe2O3/WO3 was tested during six cycles, and the magnetic materials showed an excellent removal efficiency after six cycles, with just a 7% decline.

Optimal substrate design for thermal management of high power multi-chip LEDs module

The use of light emitting diodes (LEDs) for lighting requires high level of thermal management. In fact, the lamp is more efficient when operating under lower junction temperature. In this paper, we present a three dimensional analysis of 106 W multi-chip LEDs lamp using finite element method. A comparison between two different substrate designs was carried out and showed that using separated substrates (an individual substrate for each chip) ameliorates the heat transfer rate more than the case of using one continuous substrate for all chips. The design of separated substrates was then optimized taking into account the substrate dimension, the spacing between adjacent chips and the number of chips on each substrate. It was found that using the optimal design of separated substrates instead of continuous one leads to a decrease of 14.38% of the junction temperature, an amelioration of 11.82% of the light output and an augmentation of 105212 h in the lamp lifetime.

Multi-color emitting luminescence in an Eu3+/Tb3+ co-doping borate-phosphate system CsNa2Tb2-x(BO3)(PO4)2:xEu3+

The Tb3+ and Eu3+ emissions are compossible in Tb3+/Eu3+ co-doping phosphors to realize multi-color emissions from green, yellow, orange to red, which is practical significance for light-emitting diode (LED) lamps. Hereby, we prepared a series of Tb3+/Eu3+ co-doping phosphors CsNa2Tb2-x(BO3)(PO4)2:xEu3+ (x = 0, 0.001, 0.005, 0.01, 0.02, 0.04, 0.06) and determined their crystal structure by powder X-Ray diffraction method. The energy transfer of Tb3+→Eu3+ can be verified by the overlap of Tb3+ emission and Eu3+ excitation spectra, as well as the Time-Resolved Emission Spectroscopy (TRES). The transfer efficiency of Tb3+→Eu3+ increases from 50.4% (x = 0.001) to 89.2% (0.06), resulting in the changing emitting color from green, through yellow to red. The thermostability of yellow phosphor CsNa2Tb1.999(BO3)(PO4)2:0.001Eu3+ was studied from 10 K to 450 K. At 450 K, it remains 85.93% integral intensity of that at 300 K, suggesting the good thermostability. Finally, three LEDs were fabricated using a 365 nm chip and three phosphors CsNa2Tb2(BO3)(PO4)2, CsNa2Tb1.999(BO3)(PO4)2:0.001Eu3+, CsNa2Tb1.96(BO3)(PO4)2:0.04Eu3+, which realized green, yellow and red light emissions with the CIE coordinates of (0.364, 0.570), (0.470, 0.490) and (0.662,0.336), respectively. The application significance in LED illumination or display of prepared materials is expected.

Effects of light spectrum on morpho-physiological traits of grafted tomato seedlings.

It is already known that there are many factors responsible for the successful grafting process in plants, including light intensity. However, the influence of the spectrum of light-emitting diodes (LEDs) on this process has almost never been tested. During the pre-grafting process tomato seedlings grew for 30 days under 100 μmol m-2 s-1 of mixed LEDs (red 70%+ blue 30%). During the post-grafting period, seedlings grew for 20 days under the same light intensity but the lightening source was either red LED, mixed LEDs (red 70% + blue 30%), blue LED or white fluorescent lamps. This was done to determine which light source(s) could better improve seedling quality and increase grafting success. Our results showed that application of red and blue light mixture (R7:B3) caused significant increase in total leaf area, dry weight (total, shoot and root), total chlorophyll/carotenoid ratio, soluble protein and sugar content. Moreover, this light treatment maintained better photosynthetic performance i.e. more effective quantum yield of PSII photochemistry Y(II), better photochemical quenching (qP), and higher electron transport rate (ETR). This can be partially explained by the observed upregulation of gene expression levels of PsaA and PsbA and the parallel protein expression levels. This in turn could lead to better functioning of the photosynthetic apparatus of tomato seedlings and then to faster production of photoassimilate ready to be translocated to various tissues and organs, including those most in need, i.e., involved in the formation of the graft union.

Undoped tin dioxide transparent electrodes for efficient and cost-effective indoor organic photovoltaics (SnO2electrode for indoor organic photovoltaics)

Indoor organic photovoltaics (OPVs) are currently being investigated for small-scale energy generation from artificial light sources to power small electronic devices. Despite recent progress in increasing the power conversion efficiency (PCE) of indoor OPVs, the widespread use of expensive indium tin oxide (ITO) as a transparent conducting electrode (TCE) leads to long energy payback times. This study provides a novel and comprehensive description of low-temperature atomic layer deposition (ALD)-processed indium-free tin dioxide (SnO2) films as inexpensive and efficient TCEs for indoor OPVs. These highly conformal and defect-free ALD-fabricated SnO2 films are applied to a poly(3-hexylthiophene):indene-C60 bisadduct-based OPV system. Under 1 sun illumination, an OPV with an SnO2 TCE exhibits limited operational capacity because of the high sheet resistance (~98 Ω sq−1) of the SnO2 layers. However, under a light-emitting diode (LED) lamp with a luminance of 1000 lx, the series resistance, which is related to the sheet resistance, has a marginal effect on the performance of the indoor OPV system, showing a PCE of 14.6 ± 0.3%. A reference OPV with an ITO TCE has a slightly lower PCE of 13.3 ± 0.8% under the same LED conditions. These results suggest that SnO2 TCEs can be efficient and cost-effective replacements for ITO TCEs in indoor OPV systems.

Investigating the Indoor Performance of Planar Heterojunction Based Organic Photovoltaics

Recently, the bulk heterojunction (BHJ)-based photoactive layer has been favored over the planar heterojunction (PHJ)-based photoactive layer for organic photovoltaics (OPVs), owing to the evitable thickness limit of the latter induced by the low mobility of charge carriers. However, under dim indoor light conditions, the PV performance becomes immune to the resistive components of the PHJ OPVs, such as a thick photoactive layer, thereby rendering them attractive for operating indoors. In this study, we devise and demonstrate indoor OPVs with a PHJ-based photoactive layer constituting poly(3-hexylthiophene-2,5-diyl) (P3HT) and indene-C60 bisadduct (ICBA). The performance of the PHJ OPVs was optimized by modulating the thickness of the ICBA layer under a 1000 lx light-emitting diode lamp. OPVs with a 65 nm-thick ICBA layer exhibited excellent indoor performance with a power conversion efficiency of 15.3 ± 0.3%, comparable to that of the reference BHJ OPVs (15.0 ± 0.2%). No noticeable performance degradation was observed by increasing the thickness of the PHJ-based photoactive layer; instead, a thick photoactive layer only enhanced the light absorption, resulting in excellent indoor performance with a higher photocurrent.

Recent, Bioelectricity-Related Articles Selected by Ann M. Rajnicek, Media Editor of Bioelectricity.

Recent, Bioelectricity-Related Articles Selected by Ann M. Rajnicek, Media Editor of Bioelectricity.

Photon flux density and wavelength influence on growth, photosynthetic pigments and volatile organic compound accumulation in Aeollanthus suaveolens (Catinga-de-mulata) under in vitro conditions

Aeollanthus suaveolens Mart. ex Spreng. (Lamiaceae) is an aromatic plant of African origin and is widely used in folk medicine due to its anticonvulsant and sedative effects. The aim of the study was to establish whether photon flux density (PFD) and wavelength, provided by light emitting diodes (LEDs), affect plantlet growth, photosynthetic pigment, and volatile organic compound (VOC) accumulation in Aeollanthus suaveolens. Nodal segments were grown under different PFDs (20, 57, 78, 102 and 139 μmol m−2 s−1) obtained with white LEDs lamps and under different LEDs light spectra as follows: white, green, yellow, blue, red, and combinations of red and blue (2.5R:1B; 1R:2.5B; 1R:1B) and cool white fluorescent lamps. The different light intensities affected the growth and production of photosynthetic pigments and volatile organic compounds. Plantlets grown under a PFD of 139 μmol m−2 s−1 showed greater dry weight accumulation and growth than those raised under other PFDs. The chlorophyll and carotenoid contents increased with a PFD of 20 μmol m−2 s−1. Light quality also affected plantlet growth. White LEDs light and fluorescent light were equally effective for growth and dry weight accumulation. Monochromatic red, blue, and yellow lights inhibited growth in Aeollanthus suaveolens. The concentrations of photosynthetic pigments from A. suaveolens plantlets were significantly affected by different wavelengths. Yellow wavelengths favored the production of photosynthetic pigments. The accumulation of VOCs was influenced by PFD and spectral quality.

A Heuristic Approach for Optical Transceiver Placement to Optimize SNR and Illuminance Uniformities of an Optical Body Area Network

The bi-directional information transfer in optical body area networks (OBANs) is crucial at all the three tiers of communication, i.e., intra-, inter-, and beyond-BAN communication, which correspond to tier-I, tier-II, and tier-III, respectively. However, the provision of uninterrupted uplink (UL) and downlink (DL) connections at tier II (inter-BAN) are extremely critical, since these links serve as a bridge between tier-I (intra-BAN) and tier-III (beyond-BAN) communication. Any negligence at this level could be life-threatening; therefore, enabling quality-of-service (QoS) remains a fundamental design issue at tier-II. Consequently, to provide QoS, a key parameter is to ensure link reliability and communication quality by maintaining a nearly uniform signal-to-noise ratio () within the coverage area. Several studies have reported the effects of transceiver related parameters on OBAN link performance, nevertheless the implications of changing transmitter locations on the uniformity and communication quality have not been addressed. In this work, we undertake a DL scenario and analyze how the placement of light-emitting diode (LED) lamps can improve the uniformity, regardless of the receiver position. Subsequently, we show that using the principle of reciprocity (POR) and with transmitter-receiver positions switched, the analysis is also applicable to UL, provided that the optical channel remains linear. Moreover, we propose a generalized optimal placement scheme along with a heuristic design formula to achieve uniform and illuminance for DL using a fixed number of transmitters and compare it with an existing technique. The study reveals that the proposed placement technique reduces the fluctuations in by and improves the illuminance uniformity up to as compared to the traditional approach. Finally, we show that, for very low luminous intensity, the values remain sufficient to maintain a minimum bit error rate (BER) of with on-off keying non-return-to-zero (OOK-NRZ) modulation format.

Reliability of Flip-Chip Filaments with Different Color Temperatures

Light-emitting diode (LED) lamps with different color temperatures have been widely used for various applications. Compared with LED filaments having formal vertical structures, flip-chip LED filaments have a simple structure, better heat dissipation effects, and can be formed into various shapes. In this regard, to investigate the difference in the reliability of flip-chip LED filaments with different color temperatures, this study designed and conducted three aging tests (a xenon lamp aging test, a high temperature–high humidity test, and a thermal cycling test) to simulate the application of the filaments in three outdoor environments. The luminous efficacy, CIE chromaticity coordinates, color temperature, and other indicators of the filaments were obtained before and after aging. The results showed that the high temperature–high humidity environment had the greatest impact on the filament. Particularly, the filaments with color temperatures of 4000 K and 5000 K experienced significant changes under various indicators, confirming their sensitivity to this environment. Meanwhile, the filament with a color temperature of 2700 K exhibited the best reliability. After three kinds of aging tests, the luminous efficacy of the 2700 K filaments decreased by 1.9%, 15.15%, and 0.3%, respectively, with minimal changes in various indicators, indicating their suitability for a wide range of applications.

LED and HPS Supplementary Light Differentially Affect Gas Exchange in Tomato Leaves.

Using light emitting diodes (LED) instead of conventionally used high pressure sodium (HPS) lamps as a supplemental light source in greenhouses results in a higher efficacy (µmol light per J electricity) and makes it possible to customize the light spectrum. To explore the effects of LED and HPS on gas exchange, thermal relations, photosynthesis, and water status of young tomato plants, seven genotypes were grown in a greenhouse under LED (95% red, 5% blue) or HPS lamps in four experiments differing in the fraction of lamp light over natural light. HPS lights emit a broader spectrum of red (40%), green–yellow (50%), blue (5%), and far-red (5%) and a substantial amount of infrared radiation (heat). Young tomato plants grown under LED showed lower leaf temperature and higher stomatal density, stomatal conductance (gs) and transpiration rate (E) than plants grown under HPS; this may be due to the different supplemental light spectrum. The young plants grown under LED tended to have increased photosynthetic capacity. Furthermore, the water stress indices CWSI and IG, which were obtained using thermal imaging, were positively correlated with gas exchange-derived gs and E, putting forward the use of thermal imaging for the phenotyping of transpiration. Under LED light, photosynthetic gas exchange was generally increased, which agreed with the water stress indices. The extent of this increase was genotype-dependent. All differences between LED and HPS were smaller in the experiments where the fraction of lamp light over natural light was smaller.

Heat transfer performance of the rectangular heat sinks with non-uniform height thermosyphons for high power LED lamps cooling

The rectangular heat sinks with non-uniform height thermosyphons are proposed for high power light emitting diode (LED) lamps cooling in this study. The combined thermal resistance network and finite volume method is developed to reveal the heat transfer mechanism. The simulated results show good agreement with experimental data with relative errors of 2.14–2.69% at heating powers of 12–20 W. In comparison with type-a thermosyphon heat sink, the thermal resistance of type-b thermosyphon heat sink offers 8.47–9.91% higher due to thicker thermal boundary layer between air and thermosyphon fins in the intermediary region, whereas the thermal resistance of type-c thermosyphon heat sink offers 7.26–9.07% lower because of better free stream among thermosyphon fins in the intermediary region. The maximum heat transfer rate of type-a, type-b and type-c thermosyphon heat sinks are 19 W, 17 W and 22 W in regard to the temperature threshold of 85 °C, respectively. This paper provides guidelines for the design of high power LED lamps cooling.

The Potential and Limitations of Critical Raw Material Recycling: The Case of LED Lamps

Supply risks and environmental concerns drive the interest in critical raw material recycling in the European Union. Globally, waste electrical and electronic equipment (WEEE) is projected to increase by almost 40% until 2030. This waste stream can be a source of secondary raw materials. The determination of the economic feasibility of recycling and recovering specific materials is a data-intensive, time-consuming, and case-specific task. This study introduced a two-part evaluation scheme consisting of upper continental crust concentrations and raw material prices as a simple tool to indicate the potential and limitations of critical raw material recycling. It was applied to the case of light-emitting diodes (LED) lamps in the EU. A material flow analysis was conducted, and the projected waste amounts were analyzed using the new scheme. Indium, gallium, and the rare earth elements appeared in low concentrations and low absolute masses and showed only a small revenue potential. Precious metals represented the largest revenue share. Future research should confirm the validity and usefulness of the evaluation scheme.

Evolution of Brightness and Color of the Night Sky in Madrid

Major schemes to replace other streetlight technologies with Light-Emitting Diode (LED) lamps are being undertaken across much of the world. This is predicted to have important consequences for nighttime sky brightness and color. Here, we report the results of a long-term study of these characteristics focused on the skies above Madrid. The sky brightness and color monitoring station at Universidad Complutense de Madrid (inside the city) collected Johnson B, V, and R sky brightness data, Sky Quality Meter (SQM), and Telescope Encoder Sky Sensor-WiFi (TESS-W) broadband photometry throughout the night, every night between 2010–2020. Our analysis includes a data filtering process that can be used with other similar sky brightness monitoring data. Major changes in sky brightness and color took place during 2015–2016, when a sizable fraction of the streetlamps in Madrid changed from High-Pressure Sodium (HPS) to LEDs. The sky brightness detected in the Johnson B band darkened by 14% from 2011 to 2015 and brightened by 32% from 2015 to 2019.