High Power LED Research Articles

High Power Pulsed LED Driver for Vibration Measurements.

Vibration measurements pose specific experimental challenges to be faced. In particular, optical methods can be used to obtain full-field vibration information. In this scenario, stereo-camera systems can be developed to obtain 3D displacement measurements. As vibration frequency increases, the common approach is to reduce camera exposure time to avoid blurred images, which can lead to under-exposed images and data loss, as well as issues with the synchronization of the stereo pair. Both of these problems can be solved by using high-intensity light pulses, which can produce high-quality images and guarantee camera synchronization since data is saved by both cameras only during the short-time light pulse. To this extent, high-power Light-Emitting Diodes (LEDs) can be used, but even if the LED itself can have a fast response time, specific electronic drivers are needed to ensure the desired timing of the light pulse. In this paper, a circuit is specifically designed to achieve high-intensity short-time light pulses in the range of 1 µs. A prototype of the designed board was assembled and tested to check its capability to respect the specification. Three different measurement methods are proposed and validated to achieve short-time light pulse measurements: shunt voltage measurement, direct photodiode measurement with a low-cost sensor, and indirect pulse measurement through a low-frame-rate digital camera.

BeO in epoxy composites as TIM for high-power LED packages

Beryllium oxide (BeO)-filled epoxy composite was prepared and used as a thermal interface material (TIM) in light-emitting diode (LED) packages. The filler percentages influenced on changing thermal and optical behaviour of LED at various driving currents. An improvement of 14.36% in thermal conductivity was recorded from that of neat epoxy. The lowest total thermal resistance of 10.75 K/W ( Rth) and rise in junction temperature ( Tj) of 3.1°C were recorded at 100 mA driving current for 50 wt-% BeO-filled TIM attached LED followed by an improved optical output and lowered correlated colour temperature values (3466 K). Thermal imaging infra-red imaging analysis also supported the observation of reduced Tj and Rth values from transient analysis and indicated lower chip surface temperature ( Ts) at all driving currents.

Open-source and low-cost miniature microscope for on-site fluorescence detection

The development of a compact and affordable fluorescence microscope can be a formidable challenge for growing needs in on-site testing and detection of fluorescent labeled biological systems, especially for those who specialize in biology rather than in engineering. In response to such a situation, we present an open-source miniature fluorescence microscope using Raspberry Pi. Our fluorescence microscope, with dimensions of 19.2 × 13.6 × 8.2 cm3 (including the display, computer, light-blocking case, and other operational requirements), not only offers cost-effectiveness (costing less than $500) but is also highly customizable to meet specific application needs. The 12.3-megapixel Raspberry Pi HQ Camera captures high-resolution imagery, while the equipped wide-angle lens provides a field of view measuring 21 × 15 mm2. The integrated wireless LAN in the Raspberry Pi, along with software-controllable high-powered fluorescence LEDs, holds potential for a wide range of applications. This open-source fluorescence microscope offers biohybrid sensor developers a versatile tool to streamline unfamiliar mechanical design tasks and open new opportunities for on-site fluorescence detections.

Bioinspired low temperature Cu bonding interfaces with interlocked microstructures to achieve high reliability

The reliability of Cu bonding technology in three-dimensional integration packaging is limited by high sintering temperatures and the growth of oxide at the joining interface. Hence, we propose a bionic adhesion interface of creeper sucker on the Cu substrate and covered with monolayer graphene, which increases the shear strength by 3 times compared to the conventional flat Cu substrate. The covered graphene layer effectively inhibits the generation of oxide at the joint interface and maintains a high shear strength after aging at 300 °C for 48 h Nanoscale Cu particles could reduce the chemical potential energy of the substrate surface, and stable bonding was achieved at 200 °C under a pressure of 2 MPa. Molecular dynamics simulation models reveal crystal structure evolution and residual stresses during the sintering process. This work demonstrates that bionic microstructures applied to copper bonding play an important role in interface enhancement, resulting in reliable bonding of Cu substrate at low temperatures. The method proposed here can provide insight into diversified applications including high-power light-emitting diodes soldering, SiC electronic devices, and flexible electrode interconnects.

Temperature Changes in the Pulp Chamber During Orthodontic Bonding Using a High-Power Light-Emitting Diode Device With Two Different Exposure Times and Intensities: An In-Vitro Study.

This study used a high-power light-emitting diode (LED) device to evaluate the effects of two exposure times and intensities on pulp chamber temperature and cooling time during bracket bonding. Sixty upper premolars were used in the sample in this study. These premolars were split into two main groups based on the exposure time and intensity: the first group employed a traditional curing mode (TCG) for 20 seconds with an intensity of 1200 mw/cm2, whereas the second group had a quick curing mode (QCG) for 3 seconds with an intensity of 2500 mw/cm2. The pulp chamber's temperature variations and cooling times were recorded using a thermal imaging camera. The Mann-Whitney U test was used to find differences between the two-group comparison of the pulp chamber's temperature and cooling time. The two groups had statistically significant differences regarding the temperature increase in the pulp chamber and cooling time (p > 0.001). The mean temperature increase in the traditional curing group was 3.52°C, which is greater than that in the quick curing group (i.e., a mean value of 1.28°C). The mean cooling time in the traditional curing group was 38.83 seconds, which is greater than that in the quick curing group (9.97 seconds). Reducing the exposure time to 3 secondsand increasing the intensity to 2500 mw/cm2is considered safer for the pulp chamber during and after the curing process.

Time-Resolved Ion Mobility Mass Spectrometry to Solve Conformational Changes in a Cryptochrome.

Many biological mechanisms rely on the precise control of conformational changes in proteins. Understanding such dynamic processes requires methods for determining structures and their temporal evolution. In this study, we introduce a novel approach to time-resolved ion mobility mass spectrometry. We validated the method on a simple photoreceptor model and applied it to a more complex system, the animal-like cryptochrome from Chlamydomonas reinhardtii (CraCRY), to determine the role of specific amino acids affecting the conformational dynamics as reaction to blue light activation. In our setup, using a high-power LED mounted in the source region of an ion mobility mass spectrometer, we allow a time-resolved evaluation of mass and ion mobility spectra. Cryptochromes like CraCRY are a widespread type of blue light photoreceptors and mediate various light-triggered biological functions upon excitation of their inbuilt flavin chromophore. Another hallmark of cryptochromes is their flexible carboxy-terminal extension (CTE), whose structure and function as well as the details of its interaction with the photolyase homology region are not yet fully understood and differ among different cryptochromes types. Here, we addressed the highly conserved C-terminal domain of CraCRY, to study the effects of single mutations on the structural transition of the C-terminal helix α22 and the attached CTE upon lit-state formation. We show that D321, the putative proton acceptor of the terminal proton-coupled electron transfer event from Y373, is essential for triggering the large-scale conformational changes of helix α22 and the CTE in the lit state, while D323 influences the timing.

One-Year Evaluation of High-Power Rapid Curing on Dentin Bond Strength.

This study investigated the effect of 3 s light-curing with a high-power LED curing unit on the shear bond strength of bulk-fill composites. Four bulk-fill composites were bonded to dentin with a universal adhesive (Scotchbond Universal Plus): two materials designed for rapid curing (Tetric PowerFill and Tetric PowerFlow) and two controls (Filtek One Bulk Fill Restorative and SDR Plus Bulk Fill Flowable). The 4 mm composite layer was light-cured with Bluephase PowerCure for 20 s at 1000 mW/cm2 ("20 s") or for 3 s at 3000 mW/cm2 ("3 s"). The samples were stored at 37 °C in distilled water and tested after 1, 6 and 12 months. The samples polymerised in the "3 s" mode had statistically similar or higher bond strength than the samples cured in "20 s" mode, except for the Tetric PowerFlow (1 month) and SDR+ (6 month). The flowable materials Tetric PowerFlow and SDR Plus initially showed the highest values in the "3 s" and "20 s" groups, which decreased after 12 months. The bond strength was statistically similar for all materials and curing protocols after 12 months, except for Tetric PowerFill cured with the "3 s" protocol (21.22 ± 5.0 MPa), which showed the highest value. Tetric PowerFill showed the highest long-term bond strength. While "3 s" curing resulted in equal or better shear bond strength, its use can only be recommended for a material with an AFCT agent such as Tetric PowerFill.

Telescoped Flow Synthesis of Azacyclic Scaffolds Exploiting the Chromoselective Photolysis of Vinyl Azides and Azirines.

An efficient chromoselective photochemical process is presented for the synthesis of 2H-azirines and 1,3-diazabicylo[3.1.0]hex-3-enes from readily available vinyl azides. The method exploits continuous flow photochemistry to enable the safe consumption of the hazardous azide group and provides uniform irradiation using high-power LEDs at 365-450 nm. Additionally, a scaled telescoped process has been developed providing access to drug-like 1,6-dihydropyrimidines and pyrimidines via integrated ring-expansion and oxidation reactions. Given the prevalence of various azacyclic targets in pharmaceutical, agrochemical and materials applications it is anticipated that this methodology will enable further exploitations of these important scaffolds.

Light-Emitting-Diode-Induced Fluorescence from Organic Dyes for Application in Excitation-Emission Fluorescence Spectroscopy for Food System Analysis.

An experimental study is presented on the possibility of using the fluorescence from organic dyes as a broadband light source together with a monochromator for applications in excitation-emission matrix (EEM) fluorescence spectroscopy. A high-power single-chip light-emitting diode (LED) was chosen as an excitation source with a central output wavelength at 365 nm to excite a fluorescent solution of Coumarin 1 dye dissolved in ethanol. Two excitation configurations were investigated: direct excitation from the LED and excitation through an optical-fiber-coupled LED. A Czerny-Turner monochromator with a diffraction grating was used for the spectral tuning of the fluorescence. A simple method was investigated for increasing the efficiency of the excitation as well as the fluorescence signal collection by using a diffuse reflector composed of barium sulfate (BaSO4) and polyvinyl alcohol (PVA). As research objects, extra-virgin olive oil (EVOO), Coumarin 6 dye, and Perylene, a polycyclic aromatic hydrocarbon (PAH), were used. The results showed that the light-emitting-diode-induced fluorescence was sufficient to cover the losses on the optical path to the monochromator output, where a detectable signal could be obtained. The obtained results reveal the practical possibility of applying the fluorescence from dyes as a light source for food system analysis by EEM fluorescence spectroscopy.

Increased Multiplexity in Optical Tissue Clearing-Based Three-Dimensional Immunofluorescence Microscopy of the Tumor Microenvironment by Light-Emitting Diode Photobleaching

Optical tissue clearing and three-dimensional (3D) immunofluorescence (IF) microscopy is transforming imaging of the complex tumor microenvironment (TME). However, current 3D IF microscopy has restricted multiplexity; only 3 or 4 cellular and noncellular TME components can be localized in cleared tumor tissue. Here we report a light-emitting diode (LED) photobleaching method and its application for 3D multiplexed optical mapping of the TME. We built a high-power LED light irradiation device and temperature-controlled chamber for completely bleaching fluorescent signals throughout optically cleared tumor tissues without compromise of tissue and protein antigen integrity. With newly developed tissue mounting and selected region-tracking methods, we established a cyclic workflow involving IF staining, tissue clearing, 3D confocal microscopy, and LED photobleaching. By registering microscope channel images generated through 3 work cycles, we produced 8-plex image data from individual 400 μm-thick tumor macrosections that visualize various vascular, immune, and cancer cells in the same TME at tissue-wide and cellular levels in 3D. Our method was also validated for quantitative 3D spatial analysis of cellular remodeling in the TME after immunotherapy. These results demonstrate that our LED photobleaching system and its workflow offer a novel approach to increase the multiplexing power of 3D IF microscopy for studying tumor heterogeneity and response to therapy.

Suppressing the Thermal Quenching Effect via a Cluster Conformer in Copper(I)-Iodide Coordination Polymeric Phosphors for High-Power White LED Lighting.

High-power LED lighting is a crucial challenge due to the notorious thermal quenching (TQ) effect of traditional phosphors at high operating currents, which would result in poor device performance and hamper practical optoelectronic application. Herein, we demonstrate ligand engineering of a cubane- versus staircase-like [Cu4I4] conformer as a node in coordination polymers, which remarkably suppresses the TQ effect of cluster-based photoluminescence. For complex 1 (the formula [Cu4I4(bbimb)2]n) with the cubane-like [Cu4I4] conformer as a node, the metallophilicity interaction enables ultrabright triplet emission with a photoluminescence quantum yield over 82%, and the phonon-assisted detrapping process of excitons effectively suppresses the TQ effect in the wide temperature range. In contrast, the staircase-like [Cu4I4] conformer as a node in complex 2 (the formula [Cu4I4(bbtmb)2]n) exhibits a serious TQ effect over the investigated temperature. Phosphor-converted white LEDs (pc-wLEDs) were fabricated by integrating the cluster-based coordination polymers as a color converter, and their electroluminescence performances were investigated under high bias currents. The prototype pc-wLED device by incorporating the phosphor with the suppressed TQ effect exhibits a continuous rise in brightness under a high bias current of 300 mA. The results demonstrate that ligand engineering of the cluster conformer via suppressing the TQ effect proves efficient in designing an ideal color converter for high-power pc-wLED lighting.

Uniform Lighting of High-Power LEDs at a Short Distance to Plants for Energy-Saving and High-Density Indoor Farming

A tunable LED panel with multiple types of LEDs on a panel can provide various spectra for optimal plant growth. However, it is difficult for a lighting panel with multiple types of high-power LEDs to achieve uniform lighting. We demonstrated that by using optical reflectors at the sides of an LED panel to trap photons of LED arrays or using both the above-mentioned reflectors and optical lenses on each LED, high lighting uniformity can be achieved at a short distance to plants. The ray tracing simulation results show that the LED panel equipped with reflectors and optical lenses can achieve a high uniformity of >0.80 when the LED-plant distance is at half of the LED array’s pitch. We further verified that an LED panel (at a size of 88 cm × 54 cm) installed with reflectors can achieve light uniformities around 0.90 at a 15 cm LED-plant distance for the 6 types of LEDs (4 color LEDs and 2 white LEDs) on the panel. Compared with a branded tunable LED panel, our LED panel saves >25 cm vertical distance for each tier of plants and has 92.5% higher photon efficacy for 660 nm LEDs that exist on both panels.

Enhanced efficiency of deep ultraviolet light-emitting diodes utilizing full-coverage Al reflector and highly reflective Ni/Rh p-electrode

Increasing the reflection of p-side is an effective way to improve the optoelectronic performance of flip-chip light-emitting diodes (FCLEDs). Here, we propose a full-coverage Al reflector (FAR) and a highly reflective Ni/Rh p-electrode to enhance the performance of deep ultraviolet (DUV) FCLEDs. The physical mechanism for the impact of the FAR and Ni/Rh electrode on the light extraction efficiency (LEE) is discussed theoretically. Simulations demonstrate that the combination of the FAR and Ni/Rh electrode improves the LEEs of transverse electric- and transverse magnetic-polarized light by 13.62% and 27.08%, respectively. At an injection current of 100 mA, the fabricated DUV FCLEDs with FAR and Ni/Rh electrode exhibits an external quantum efficiency of 4.01% and a wall plugging efficiency of 2.92%, which are 16.85% and 13.18% higher than those of conventional DUV FCLEDs, respectively. These results support the promise of the FAR and Ni/Rh electrode for high-power DUV LED applications.

Spectrum regulation of LuAG:Ce phosphor ceramic with Gd doping for high-brightness and high-power yellow-emitting LEDs applications

To realize the high-brightness of yellow light-emitting diodes (LEDs), the yellow-emitting phosphor ceramics with high luminous efficiency (LE) are urgently explored. Based on the idea of spectrum regulation, the Lu3-x-yGdyAl5O12:xCe3+ (LuGdAG:Ce) phosphor ceramics were prepared via vacuum solid-state sintering. The effect of Gd3+ and Ce3+ content on the structure, luminescence and thermal properties of LuAG:Ce ceramics were investigated. The distortion ratio (D) of CeO8 and bandgap were effectively modified via Gd3+ doping, resulting in massive red-shifting of Ce3+ emission (513→561 nm). The LEDs lighting encapsulated by LuGdAG:Ce ceramics changes from green to yellow. Importantly, the yellow LEDs with a LE up to 139.0 lm/W@180 W and a warm correlated color temperature (CCT) of 3620 K were achieved based ceramic Ce07Gd9. The LuGdAG:Ce phosphor ceramic has the best of luminescence performance in phosphor-converted yellow LEDs lighting so far, which is considered to be the highly promising color converter.

Enhancement of thermal conductivity and insulation of silicone thermal interface material through surface modification and synergistic effects of nanofillers for thermal management of electronic devices

Thermal interface materials (TIMs) play an irreplaceable role in highly integrated microelectronic devices. In this work, the addition of acidified carbon nanotubes modified by 3-aminopropyl triethoxysilane (KH550) had an effective enhancement to the thermal conductivity, thermal stability, and electrical insulation performance of silicone grease. On this basis, multi-filled silicone grease composites with better thermal conductivity and electrical insulation were prepared by introducing zinc oxide (ZnO) and Graphene nanoflakes (GNFs). The thermal conductivity of silicone grease achieved 1.438 W m−1 K−1, while the volume resistivity still exceeded 1013 Ω·cm. Additionally, the study explored the impact of varying filler parameters, temperature, and contact pressure on the interface thermal contact resistance of silicone grease. The best performance silicone grease applied to the cooling of the high-power LED exhibited excellent heat dissipation. This work presented a reference for the design and development of low cost, high performance TIMs.

Optimized method of thermoelectric cooler-based thermal management for improving the luminous efficacy of light-emitting diodes

We experimentally performed a method of active cooling for white LED that can reduce the temperature of the LED by using TEC for reducing the temperature of the LED board. The relation of LED board and input power for TEC was investigated to find out the optimized curve of LED board temperature and input power for TEC. Also, the TEC based cooling system was applied for RGBW LEDs. The obtained result is meaningful in LED thermal management, improving the lighting quality and increases the lifespan for both middle and high-power LED types. Full Text: PDF References E.F. Schubert, J.K. Kim, "Solid-State Light Sources Getting Smart", Science, 308, 1274 ¬(2005). CrossRef Q.K. Nguyen, "Emission spectrum modeling of white LEDs light source with using Gaussian function", Photonics Lett. Pol.,15(4), 54 (2023). CrossRef C.C. Sun, S.H. Ma, Q.K. Nguyen, "Advanced LED Solid-State Lighting Optics", Crystals, 10, 758 (2020). CrossRef S.P. Ying, H.K. Fu, W.F. Tang, R.C. Hong, "The Study of Thermal Resistance Deviation of High-Power LEDs", IEEE Trans. Electron Devices, 61, 2843 (2014). CrossRef K. Górecki, P. Ptak, "Compact Modelling of Electrical, Optical and Thermal Properties of Multi-Colour Power LEDs Operating on a Common PCB", Energies, 14, 1286 (2021). CrossRef C.C. Sun, Q.K. Nguyen, T.X. Lee, S.K. Lin, C.S. Wu, T.H. Yang, Y.W.Yu. "Active thermal-fuse for stopping blue light leakage of white light-emitting diodes driven by constant current", Sci. Rep. 12, 12433 (2022). CrossRef Q.K. Nguyen, B. Glorieux, G. Sebe , T.H. Yang, Y.W. Yu , C.C. Sun, "Passive anti-leakage of blue light for phosphor-converted white LEDs with crystal nanocellulose materials", Sci Rep. 13, 13039 (2023). CrossRef N. Bădălan (Drăghici), P. Svasta, C. Marghescu, "A Method for Improving an Active Cooling Solution for LEDs ", IEEE 24th International Symposium for Design and Technology in Electronic Packaging (SIITME), Iași, Romania (2018). CrossRef A. Fan, R. Bonner, S. Sharratt, Y.S. Ju, "An innovative passive cooling method for high performance light-emitting diodes", 28th Annual IEEE Semiconductor Thermal Measurement and Management Symposium (SEMI-THERM), 319-324 (2012). CrossRef D.W. Kim, E. Rahim, A. Bar-Cohen, B. Han, "Direct Submount Cooling of High-Power LEDs", Compon. Packag. Technol., 33, 698 (2010). CrossRef N. Guan, N. Amador-Mendez, A. Kunti, A. Babichev, S. Das, A. Kapoor, N. Gogneau, J. Eymery, F.H. Julien, C. Durand, M. Tchernycheva, "Heat Dissipation in Flexible Nitride Nanowire Light-Emitting Diodes", Nanomater, 10, 2271 (2020). CrossRef S. Li, J.L. Liu, L. Ding, J.X. Liu, J. Xu, Y. Peng, M.X. Chen, "Active Thermal Management of High-Power LED Through Chip on Thermoelectric Cooler", IEEE Trans. Electron Devices, 68, 1753 (2021). CrossRef G.R. Sui, J.J. Chen, H. Ni, Y.Y. Ma, X.M. Gao, N. Wang, "Improvement of LED Performance With an Integrated Thermoelectric Cooling Package", IEEE Access, 8, 116535 (2020). CrossRef

Self‐powered HP‐LED intelligent energy management system with adaptive brightness adjustment

AbstractThe energy harvesting system achieved from one environmental energy channel is facing more and more challenges in meeting the power supply of electronic energy‐consuming devices. In this study, a combined photovoltaic (PV) and Thermoelectric Generator (TEG) energy management system is proposed with intelligent self‐powered technique for high‐power light‐emitting diodes (HP‐LED) lighting. Both the solar energy and waste heat induced by PV and HP‐LED are synchronously converted into electrical energy. Self‐powered by this gathered power, an adaptive light intensity control of HP‐LED is also realized using the established feedback path between ambient light and HP‐LED light. Experimental results show that the supply voltage of the TEG required for startup of the whole system can be decreased as 20.8 mV. Only 10 s is needed to complete the startup process under sufficient light, while 25 s in case of insufficient conditions. This energy management can provide a new technology for future smart home and greenhouse planting.

Identification and Measurement of Biomarkers at Single Microorganism Level for In Situ Monitoring Deep Ultraviolet Disinfection Process.

Since the COVID-19 disease has been further aggravated, the prevention of pathogen transmission becomes a vital issue to restrain casualties. Recent research outcomes have shown the possibilities of the viruses existing on inanimate surfaces up to few days, which carry the risk of touch propagation of the disease. Deep ultraviolet germicide irradiation (UVGI) with the wavelength of 255-280nm has been verified to efficiently disinfect various types of bacteria and virus, which could prevent the aggravation of pandemic spread. Even though considerable experiments and approaches have been applied to evaluate the disinfection effects, there are only few reports about how the individual bio-organism behaves after ultraviolet C (UVC) irradiation, especially in the aspect of mechanical changes. Furthermore, since the standard pathway of virus transmission and reproduction requires the host cell to assemble and transport newly generated virus, the dynamic response of infectious cell is always the vital aspect of virology study. In this work, high power LEDs array has been established with 270nm UVC irradiation to evaluate disinfection capability on various types of bio-organism, and incubator embedded atomic force microscopy (AFM) is used to investigate the single bacterium and virus under UVGI. The real-time tracking of the living Vero cells infected with adenovirus has also been presented in this study. The results show that after sufficient UVGI, the outer shell of bacteria and viruses remain intact in structure, however the bio-organisms lost the capability of reproduction and normal metabolism. The experiment results also indicate that once the host cell is infected with adenovirus, the rapid production of newborn virus capsid will gradually destroy the cellular normal metabolism and lose mechanical integrity.

Study on Illuminance Control based on Arduino Method

The paper presents a method for achieving constant illumination control by integrating various technologies, including Arduino technology, LED driver technology, and control technology. The HV9910B constant current drive chip is used to design a high-power LED driver in the form of an Arduino expansion board. The performance of the driver is tested, including efficiency testing and waveform testing. The PID control library of Arduino is utilized to write the control program rapidly. Illumination control experiments are conducted with expected results.

Design and testing of a high-performance solar LED streetlight

This paper presents the development and validation of a high-performance solarpowered charging streetlight. Our controller incorporates various charging modes, including MPPT charging, constant current charging, and constant voltage charging, and the controller can automatically change the charging mode based on the battery level. The streetlight can achieve brightness adjustment through PWM adjustment. The controller turns off the streetlights once the battery voltage reaches the over-discharge protection voltage. However, turning off the streetlights inevitably results in a voltage rebound above the over-discharge protection voltage. Consequently, the streetlights enter a cycling pattern of illumination and extinguishment. We have addressed this issue by incorporating a voltage rise threshold in the controller program, effectively preventing the streetlights from cycling between illumination and extinguishment. The MCU (Micro Controller Unit) can output multiple sets of PWM waves, where each set can control the on/off state of an LED light group. Combining multiple LED groups enables the driving and control of high-power LED street lights. We designed and constructed two solar-powered LED lighting systems to demonstrate the practicality of our approach. Extensive long-term outdoor field tests validate the robust performance of our control system.