High Power LED Research Articles

Adaptive museum lighting using CNN-based image segmentation

Modern smart lighting systems have the potential to improve lighting conditions by employing adaptive dimming. However, the light intensity pattern of the individual luminaires is often not optimally matching with the region(s) of interest. By using adaptive lighting fixtures with a tunable radiation pattern, much more targeted illumination can be enabled. The already demonstrated adaptive lighting fixtures are typically quite bulky, and require user input to optimize the emitted light. In this paper, a compact lighting fixture is proposed that consists of a high-power LED, a sequence of lenses, an adjustable mirror and tunable diffuser, to achieve an adaptive lighting functionality. This adaptive luminaire is integrated with an embedded system and camera, to realize autonomous beam adjustment based on computer vision in a museum setting. The embedded system performs semantic segmentation to detect painting masks, and adapts the light beam direction and spot size to the detected painting frame via a feedback loop. The system can be considered as a first demonstration of the integration between state-of-the-art computer vision and adaptive light fixtures for indoor lighting.

High-performance thermal management system for high-power LEDs based on double-nozzle spray cooling

Thermal management is one of the main challenges for high-power LEDs. As one of the state-of-the-art thermal management approaches, spray cooling can meet the requirements of fast cooling speed, large heat transfer coefficient, and less energy consumption when it provides thermal management for electronics with high heat flux. In this study, a high-performance spray cooling system for high-power LEDs is designed and established. The influence of nozzle configuration, flow rate, and nozzle-to-surface distance on the heat transfer characteristics are experimentally and numerically investigated. The system shows excellent heat dissipation capacity. Two different nozzle configurations are compared and the results show that the double-nozzle configuration possesses the highest single-phase heat transfer coefficient, reaching up to 20.7 kW/m2·K with the flow rate of 150 mL/min. Interestingly, double-nozzle, which owns better heat transfer performance compared to single-nozzle, shows worse temperature uniformity inside the testing module. Simultaneously, the junction temperature of double-nozzle at the center chip can also be controlled to 85 °C corresponding to a 10% reduction for single-nozzle. The proposed cooling system may enable the further application of spray cooling in electronics like high-power LEDs, potentially reducing the energy consumption in cooling electronics and promoting the utilization of low-grade thermal energy.

Two-step sintered phosphor ceramics for high-power LED applications: Fine microstructure and luminescent property

With the development of the high-power solid-state lighting (SSL) industry, there is an urgent demand for low-cost color converters with good luminescent performance and thermal robustness. Conventional phosphor ceramics face the problems of high sintering energy consumption and low light extraction efficiency. In the present work, a two-step sintering (TSS) method has been developed to obtain a series of YAG:Ce and YAG:Ce-Al2O3 samples at a lower temperature of 1600 °C, where the operating power is reduced to 67% of the traditional one-step process. The TSS samples have a fine microstructure, which leads to a better scattering enhancement effect. The impacts of grain size and composition on optical and thermal properties were investigated in detail. The luminous characteristics and stability were analyzed by packaging phosphor ceramics with blue LEDs, with a maximum LE of 188.72 lm/W, CRI of 58.7, and CCT in the range of 3628–5048 K, respectively. Such suitable properties of the TSS material make it a promising candidate for high-power white LEDs applications.

Continuous-Flow Synthesis of Cyclobutenes Using LED Technology

AbstractCyclobutenes are highly strained ring systems of considerable synthetic interest that can be accessed via cycloaddition reactions between alkenes and alkynes. However, their traditional preparation relies on photochemical [2+2] cycloadditions that exploit low-wavelength UV radiation emitted from inefficient medium-pressure Hg lamps. This paper reports on the development of a modern approach using a high-power LED set-up emitting at the boundary of UV-A and visible light in conjunction with a continuous-flow reactor. The resulting flow process renders a series of cyclobutenes from maleimides and various commercial alkynes. This provides a more energy-efficient approach that is readily scalable to access multigram quantities of cyclobutenes in high chemical yields and short residence times. The value of these products is exemplified by flow-based hydrogenations yielding highly substituted cyclobutanes which represent sought after building blocks in modern medicinal chemistry programs.

Impact of a High-Power Light-Emitting Diode Unit With Reduced Curing Times on the Shear Bond Strength of Orthodontic Brackets and Their Adhesive Remnant Index Scores.

This study aims to evaluate the curing time minimally required for bonding stainless-steel (SS) brackets using a high-power light-emitting diode (LED) light curing unit (LCU) and examine the debonded enamel surface for adhesive remnant. Based on the LED LCU and curing time employed, 80 human maxillary first premolar teeth were equally segregated into four groups. Three groups were cured using a high-power LED unit (Guilin Woodpecker Medical Instrument Co., Ltd., Guilin, Guangxi, China) for one, two, and three seconds. The fourth group served as a control and was bonded with another intensive LED unit (Elipar™ S10 LED Curing Light; 3M, Saint Paul, Minnesota, United States) for 20 seconds. Transbond™ XT Light Cure Adhesive (3M, United States) adhesive was used for bonding the SS brackets. All the samples were exposed to shear bond strength (SBS) testing after a 24-hour immersion period in distilled water at 37°C. A stereomicroscope was used to examine and score the adhesive remnant on the debonded surface using a modified adhesive remnant index (ARI). Kruskal-Wallis-ANOVA and post-hoc Mann-Whitney U tests for multiple pairwise comparisons were performed to analyze the data. Time and intensity significantly affected the SBS (P<0.001). A higher SBS value (16.04 megapascals (MPa)) was obtained in the six-second group when compared to the three-second (11.58 MPa), one-second (10.69 MPa), and 20-second control (13 MPa) groups. The ARI was significantly affected by the curing method. Higher SBSs were recorded for the six-second group using the high-power LED. A greater ARI score is associated with a reduced curing duration and vice versa.

Vertically Aligned Boron Nitride Nanosheets Films for Superior Electronic Cooling.

Thermally conductive and electrically insulating thermal interface materials (TIMs) are highly desired for electronic cooling. To improve heat transfer efficiency, thermally conductive fillers with a high loading content have been incorporated into the polymer-based TIMs. However, this is usually at the expense of the interfacial thermal resistance reduction and reliability. In this study, vertically aligned boron nitride nanosheet films (VBNFs) have been prepared by a scalable microfluidic spinning process and template-assisted chemical vapor deposition conversion method. A further high-temperature annealing was applied to achieve high crystallinity. VBNFs have been applied as fillers to fabricate TIMs and achieve a superior through-plane thermal conductivity of 6.4 W m-1 K-1 and low modulus of 2.2 MPa at low BN loading of 9.85 vol %, benefitting from the well-aligned vertical sheet structure and high crystallinity. In addition, the fabricated TIMs present high-volume resistivity and breakdown strength, satisfying the electrical insulation demands. The high thermal conductivity and low modulus contribute an outstanding cooling performance to the TIMs in the heat dissipation application for high-power LEDs. This template-assisted conversion technology for the fabrication of orientated BN nanosheets structure and the prepared high-performance TIMs pave the way for efficient thermal management of high-power electronics.

Simulation study of nanomaterials in heat pipe enhanced high power LED heat sink

To facilitate the simulation of heat dissipation of high-power LED lamps, a set of simplified models for tubular heat pipes and carbon nanotube arrays were first established to estimate their thermal conductivity. Then several kinds of radiators were designed. The application of nanomaterials and heat pipes in the heat dissipation of lamps was studied by the finite element method. It is found that the radiator with vertical suspended fins strengthened by a heat pipe and heat dissipation coating has a better heat dissipation effect than other radiators. Finally, the simulation study of thermal interface materials and heat dissipation coatings for lamps and lanterns heat dissipation is carried out. The results show that the thermal interface materials of carbon nanotubes and carbon nano coatings can enhance the heat dissipation performance of lamps.

Improved luminescence and high thermal stability in translucent SrBaSiO4 ceramic disc for high power LED

Improved luminescence and high thermal stability in translucent SrBaSiO4 ceramic disc for high power LED

ADHERENCE REDUCTION OF PSEUDOMONAS AERUGINOSA UFPEDA 416 UNDER BLUE LED LIGHT IRRADIATION AND CURCUMIN EXPOSURE

This study assessed the adhesion of Pseudomonas aeruginosa UFPEDA 416 (ATCC 27853) exposed to curcumin-mediated Photodynamic Antimicrobial Chemotherapy (PACT). Initially, the Minimum Inhibitory Concentration of curcumin was determined (0.63 μg/mL). After, P. aeruginosa UFPEDA 416 was exposed to the MIC solution of curcumin and then irradiated with a high-power blue LED light at 480 nm for 20, 40, 60 and 120 minutes (28.03 mW/cm2). At each interval, 100 µL aliquots were transferred to microtubes containing Müeller-Hinton broth and incubated at 30ºC for 24 h. The biofilm formed was quantified by the crystal violet method. The adherence rate was calculated using the difference in the absorbance of the treatment, compared to the control. There was a reduction in adhesion capacity from 40.8% in the first 20 minutes to approximately 11% after 60 minutes. The reduction in the adhesion rate accompanied the decrease in planktonic cells, determined from the measurement of the absorbance of the supernatant at 620 nm. The results indicated action by bacteriostasis.

Significantly thermally conductive cellulose composite film with graphene/boron nitride heterojunction structure achieved by combustion synthesis

Boron nitride nanosheets (BNNSs) have been regarded as promising fillers to fabricate polymer-based composites for thermal management. However, the thermal resistance between BNNSs seriously restricts the further improvement of thermal conductivity (TC) for BNNS-based polymer composites. Herein, a rapid and high-yield method based on a combustion synthesis technique is developed to combine BNNSs and graphene (G) tightly as a hybrid filler, in which G was in-situ grown on the surface and interlayer of BNNSs, forming a special G@BNNS heterojunction structure. A foldable and thermal conductive composite film made of such G@BNNS filler and cellulose nanofiber (CNF) matrixes through filtration exhibits high in-plane and through-plane TC of 125.0 and 2.1 W/(m K), respectively. Such high TC is attributed to the reduced interfacial thermal resistance because of the high order and strong bridging effect of G with BNNSs. By utilizing this composite film as a heat spreader, heat dissipation is demonstrated effectively in high-power LED devices under high-power conditions over numerous cycles and heat dissipation can be carried out uniformly in the in-plane direction. Our findings indicate that G@BNNS/CNF films can meet both performance of maintenance and heat dissipation for thermal management, which are much needed for modern electronic devices.

Improved wavelength stability and heat dissipation of InGaN-based light-emitting diodes using a graphene interlayer on patterned sapphire substrate

This study presents a straightforward strategy that embeds a graphene interlayer between InGaN-based light-emitting diodes (InGaN LEDs) and patterned sapphire substrate (PSS substrate) for substantial improving device performances of wavelength stability and heat dissipation. The InGaN LEDs on the graphene interlayer/PSS substrate (Gr-LED) have lower piezoelectric fields of 1.16 MV/cm than 1.60 MV/cm for InGaN LEDs on the PSS substrate (Ref-LED). The low piezoelectric field diminishes the screen of the polarization field resulting in a stable electroluminescence peak wavelength. At 100 mA driving current, the chip temperature of Gr-LED shows a decrease in around 24.4 °C relative to Ref-LED. The thermal resistances measured in a vacuum environment are 351 and 128 °C/W for Ref-LED and Gr-LED, respectively. The low thermal resistance of Gr-LED is believed to be due to a low misfit dislocation density of the aluminum nitride nucleation layer that increases the vertical direction of heat transport to PSS. This work demonstrates that the graphene/PSS substrate is a promising substrate for high-power InGaN LEDs.

Stable Polyhedron-Cluster-Based Rigid Fluoride Framework toward Zero-Thermal-Quenching Near-Infrared Emission for Prolonged LED Applications.

Development of highly thermally stable broadband near-infrared (NIR) luminescence materials is crucial for advancing the prolonged stable application of smart NIR light sources. In this study, a zero-thermal-quenching and reversible temperature-dependent broadband NIR-emitting Cs2NaAl3F12:Cr3+ phosphor is demonstrated, benefiting from its stable polyhedron-cluster-building rigid structure. The excellent thermal stability of Cs2NaAl3F12:Cr3+ is rooted in its stable [Al6Na4F45] cluster building unit, which provides a rigid structure with a weak electron-phonon coupling effect and a wide band gap with a huge thermal activated barrier. Such characteristics are well revealed by multiple studies on crystal structure, electronic structure, Huang-Rhys factor S, configuration coordinate model, and Debye temperature. The incorporation of Li or K instead of Na weakens the luminescence thermal stability, directly proving the importance of the stable [Al6Na4F45] cluster for stable Cr3+ substitution and rigid structure construction. Furthermore, Cs2NaAl3F12:Cr3+ presents much superior thermal stability compared to traditional rigid garnet-type fluorides Na3X2Li3F12:Cr3+ (X = Al, Ga, In). A high-power NIR LED is presented, utilizing the high quantum efficiency (∼71%) and extremely thermally stable broadband NIR emission around 750 nm of Cs2NaAl3F12:Cr3+. It realizes clear vein and cartilage imaging in the human hand, demonstrating its potential in medical diagnosis applications. This result provides important insights for designing new-type rigid crystal structures using stable polyhedron clusters as basic units, advancing the development of highly thermally stable NIR-emitting phosphors.

Reactive SPS of Al2O3–RE:YAG (RE = Ce; Ce+Gd) composite ceramic phosphors

Ultrafine-grained Al₂O₃−RE:YAG (RE=Ce; Ce+Gd) composite ceramics were obtained for the first time by reactive SPS using commercially available initial oxide powders. The effect of key sintering parameters (temperature and dwell time, external pressure) on densification peculiarities, structural-phase state, and luminescent properties of composites was studied comprehensively. Differences in phase formation and densification between Ce-doped and Ce,Gd-codoped systems were shown. Parameters of reactive SPS at which there is partial melting with the formation of near-eutectic zones of the Al₂O₃−YAG system/coexistence of several variations of the YAG-type phase were established. Pure corundum-garnet biphasic ceramics with an optimal balance between microstructural and luminescence performance were synthesized at 1425°C / 30 min / 30-60 MPa. The external quantum efficiency of the phosphor converters reached 80.7% and 72% with close lifetimes of ~63.8 nsec, similarly to commercial Ce:YAG materials, which is promising for further application in the field of high-power white LEDs and LDs.

Light Extraction of Near-Infrared AlGaAs-Based LED Enhanced by Nanostructured Surface Morphology

To improve the light extraction efficiency of a planar AlGaAs-based light emitting diode (LED) (Device A), three novel LEDs with nanostructured surface morphologies are prepared using a surface texturing approach. We describe the fabrication of a nanostructured light extraction enhancement layer via the annealing of an evaporated Ag layer. Thermal annealing is used to induce the restructuring of a 15–25 nm layer of electron beam evaporated Ag into “nanoparticles”, which are used as an etch mask to transfer a nanopattern into the n-AlGaAs layer. Then, the Ag is removed, and the remaining nanostructured n-AlGaAs surface improves the extraction of light from the device. The novel LEDs have three different nanostructured thicknesses, namely 15 nm (Device B), 20 nm (Device C), and 25 nm (Device D). The morphologies of the Devices B–D are analyzed by an atomic force microscope and a scanning electron microscope. Compared to the planar LED (Device A), the light output powers of the Devices B–D increases by 112.6%, 91.4%, and 63.5%, respectively. The nanopatterns can mitigate the abrupt change of the refractive indexes between the air and the semiconductor to increase the LEDs’ light extraction efficiency. The surface texturing approach can be applied to commercial high-power LEDs.

High luminous efficiency of a phosphor-in-glass plate by optimization of the glass and phosphor content for high-power LED applications

Generally, white light-emitting diodes (LEDs) are fabricated by combining blue LED chips with yellow phosphors. When fabricating white LEDs, the phosphor is typically mixed with an organic resin and applied to the LED chips as a paste. A phosphor-in-glass (PiG) plate can alternatively be used to address the poor high-temperature reliability of the paste method. However, because pores form in the PiG plate during the sintering process, this method results in a loss of optical efficiency. Accordingly, we aimed to improve the fluidity of glass and light efficiency by optimizing the sintering temperature of the glass powder and the phosphor content respectively for reducing internal porosity in the PiG. In this study, glass powder was sintered at different temperatures to produce glass plates, while also varying the phosphor content to fabricate PiG plates. The optimal light characteristics were realized with a glass sintering temperature of 640 °C and a phosphor content of 20 wt%.

Energy estimation of the post-treatment process for powder aerosol deposited solid electrolyte films

In this study, the post-annealing process of garnet-type electrolyte films produced by the powder aerosol deposition method was optimized by utilizing high-power LEDs. The post-annealing time was greatly reduced from hours to several seconds. The film conductivity at room temperature could be increased by three orders of magnitude from 5.0 ⋅ [Formula: see text] S [Formula: see text] to 5 ⋅ [Formula: see text] S [Formula: see text]. For the first time, the required energy for this almost complete conductivity restoration could be quantitatively estimated.

(Sr,Ca)AlSiN3:Eu2+ phosphor-in-glass and YAG ceramic composites for high CRI and high-power white LEDs

A series of red-emitting (Sr,Ca)AlSiN3:Eu2+ phosphor-in-glasses (SCASN PiGs) were successfully prepared by spin coating. The optical, thermal and luminescence performance of the SCASN PiGs with different ratios of phosphor to glass (P1G4, P1G3, P1G2 and P1G1) were investigated systematically. The thermal stabilities of SCASN PiGs are superior to (Sr,Ca)AlSiN3:Eu2+ phosphor. As the P1G2 sample was coupled with blue LED chips, warm white light with luminous efficacy (LE) of 115.60 lm/W, color rendering index (CRI) of 73.6 and correlated color temperature (CCT) of 2750 K was achieved running in 100 W COB model. In addition, the CRI of YAG-P1G2 sample was improved to 81.7 when a YAG ceramic was added. These results suggested that the YAG-SCASN PiG is a promising candidate for high CRI and high-power (hp) WLEDs.

Improve the secondary structure of the series ionic wind generator to regulate the flow distribution and its application in electronics cooling

The substantial amount of heat released by power electronic devices as they go toward increasing frequency and higher integration offers significant challenges for electronics cooling. Dual-stage ionic wind generators with a V-shaped ‘needles-to-rings' design are presented. To achieve higher cooling efficiency, the ionic wind flow distribution was managed by improving the structure of the sub-unit. The calculation was performed using a two-dimensional model. By coupling an electric field, flow field, the development of ionic wind flow was simulated. Experiments were carried out in order to assess the EHD properties of the designed ionic wind generators, as well as the cooling impact on a high-power LED chip. The findings show that the convergent outlet structure has several defects, resulting in large momentum loss. The dual grounded rings in the sub-unit may spread the ionic wind more efficiently, providing charged particles with a stronger forward driving force and more possibilities to produce ionic wind. The ionic wind has a wide distribution range, a maximum wind velocity of 2.46 m/s, and provides improved cooling for the LED chip.

Current State and Prospects for Development of Head Lighting for Vehicles. Part 2. Advanced Designs for Vehicle Headlights

As it has been shown in part 1 of this paper, modern head lighting, due to objective design flaws, does not always meet the requirements of existing international standards, which means a decrease in road safety. To eliminate the previously Multibeam type. These types of headlights are currently either undergoing the stage of production tests or are used in extremely limited batches of vehicles in terms of the number of produced units. According with the results of this analysis, recommendations have been formulated for the design of advanced head lighting. The main of these recommendations is the use of single high-power LEDs with total internal reflection reflectors, which will provide a sharp cut-off border with efficient use of the source light flux. To increase the resistance of the headlight to temperature rise, it is proposed to use LEDs or other economical light sources together with phosphor parts. It is shown that adaptability is a useful but optional property of vehicle headlights, since it leads to complicate the design, and this is not always justified. The advantages of the headlight, created taking into account the above recommendations, are described, the main of which are the simplification of its design, reduction in weight and improvement of the thermal parameters of the product.

Core-Shell Structured Fluorescent Protein Nanoparticles: New Paradigm Toward Zero-Thermal-Quenching in High-Power Biohybrid Light-Emitting Diodes.

Stable and efficient high-power biohybrid light-emitting diodes (Bio-HLEDs) using fluorescent proteins (FPs) in photon downconverting filters have not been achieved yet, reaching best efficiencies of 130lm W-1 stable for >5h. This is related to the rise of the device temperature (70-80 °C) caused by FP-motion and quick heat-transmission in water-based filters, they lead to a strong thermal emission quenching followed by the quick chromophore deactivation via photoinduced H-transfer. To tackle both issues at once, this work shows an elegant concept of a new FP-based nanoparticle, in which the FP core is shielded by a SiO2 -shell (FP@SiO2 ) with no loss of the photoluminescence figures-of-merit over years in foreign environments: dry powder at 25 °C (ambient) or constant 50 °C, as well as suspensions in organic solvents. This enables the preparation of water-free photon downconverting coatings with FP@SiO2 , realizing on-chip high-power Bio-HLEDs with 100lm W-1 stable for >120h. Both thermal emission quenching and H-transfer deactivation are suppressed, since the device temperature holds <40 °C and remote high-power Bio-HLEDs exhibit final stabilities of 130 days compared to reference devices with water-based FP@SiO2 (83 days) and FP-polymer coatings (>100h). Hence, FP@SiO2 is a new paradigm toward water-free zero-thermal-quenching biophosphors for first-class high-power Bio-HLEDs.