High-brightness Light-emitting Diodes Research Articles

A Novel Version of the Ripple-Modulation Technique for Enabling the Use of Single-Phase Buck Converters in VLC Applications

Visible light communication (VLC) has recently emerged as a promising technology for alleviating the saturation of the radio frequency (RF) spectrum. VLC uses high-brightness light-emitting diodes (HB-LEDs) both for lighting and communication. In particular, the information transmission is carried out by performing fast changes of the light intensity emitted by the HB-LEDs. The conventional VLC driver includes a linear power amplifier (LPA) for reproducing the communication signal. Unfortunately, this approach penalizes the efficiency. During the last years, a wide variety of VLC drivers fully based on the use of switching-mode power converters (SMPCs) have been proposed to overcome the efficiency limitation. One of the most promising approaches is the ripple-modulation (RM) technique, which consists in using the output voltage ripple of an SMPC to reproduce the communication signal. However, the conventional RM technique has a major drawback: it can only be applied to multiphase buck converters. This work is focused on overcoming that limitation by introducing a novel version of the RM technique that enables the use of a single-phase buck converter. In this way, the work aims to reduce the required power-stage complexity, which is a critical parameter of HB-LED bulbs. Moreover, a novel output filter structure is proposed to reduce the total harmonic distortion of the reproduced signal. A ripple-modulated buck converter prototype was built with an output power and a switching frequency of 8 W and 2 MHz, respectively. Moreover, the reproduced passband modulation scheme provides a bit rate of up to 1.25 Mb/s with a communication range of 100 cm and a peak efficiency of 94%.

Optimization of heat-dissipated structures with cuprous oxide deposits to improve thermal management of high-brightness LED arrays

This project reports on improving the thermal performance of light-emitting diode (LED) packages based on an optimized thermal structure with a sprayed cuprous oxide coating. Eighteen orthogonal arrays of LED aluminum plates were used and the influence of the parameters of thermal dissipation structure on the LED junction temperature was established. The junction temperature of the LED assembly is developed by various heat dissipation structures based on Taguchi methods. The experimental results show that by measuring the temperature of the 12W LED module, the best results were compared with the lowest values in the overall experiment, where the junction temperature dropped from 67°C to 51°C Also, the contribution of the error to the total variance is about 0.8%, indicating that the experiment is quite successful and robust results. It was found that lower junction temperature values were obtained with optimized heat sink structures with Cu2O-coated Al substrates, and the thermal performance of the LEDs was further improved.

Efficient Synthetic Aperture for Phaseless Fourier Ptychographic Microscopy with Hybrid Coherent and Incoherent Illumination (Laser Photonics Rev. 17(3)/2023)

Efficient Synthetic Aperture for Phaseless Fourier Ptychographic Microscopy In article number 2200201, Qian Chen, Chao Zuo, and co-workers introduce an efficient synthetic aperture for phaseless Fourier ptychographic microscopy (ESA-FPM), which employs both coherent and incoherent illuminations to maximize the efficiency of data and achieve high spatial-bandwidth product reconstruction with few acquisitions. Furthermore, 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.

LED Systems Applications and LED Driver Topologies: A Review

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

Quantum shells versus quantum dots: suppressing Auger recombination in colloidal semiconductors.

Colloidal semiconductor nanocrystals (NCs) have attracted a great deal of attention in recent decades. The quantum efficiency of many optoelectronic processes based on these nanomaterials, however, declines with increasing optical or electrical excitation intensity. This issue is caused by Auger recombination of multiple excitons, which converts the NC energy into excess heat, whereby reducing the efficiency and lifespan of NC-based devices, including lasers, photodetectors, X-ray scintillators, and high-brightness LEDs. Recently, semiconductor quantum shells (QSs) have emerged as a viable nanoscale architecture for the suppression of Auger decay. The spherical-shell geometry of these nanostructures leads to a significant reduction of Auger decay rates, while exhibiting a near unity photoluminescence quantum yield. Here, we compare the optoelectronic properties of quantum shells against other low-dimensional semiconductors and discuss their emerging opportunities in solid-state lighting and energy-harvesting applications.

Formation of multiple aerial LED signs in multiple lanes formed with AIRR by use of two beam splitters

We propose multiple aerial imaging system by use of two beam splitters in the optical system of aerial imaging by retro-reflection (AIRR). The AIRR optical system consists of a light source, a beam splitter, and a retro-reflector. Use of two-layered beam splitters enables us to show multiple aerial signs to drivers in multiple driving lanes. The purpose of this paper is to confirm feasibility that an aerial display by use of AIRR for a novel traffic information provision. First, we explain an optical configuration to show aerial images to multiple road lanes, a driving lane and an overtaking lane with AIRR by use of two beam splitters. Next, we have developed a prototype optical system by use of two large beam splitters and a large high-brightness LED sign that is designed to be used for actual road displays. The light source was an LED display with a height of 450 mm and a width of 390 mm, which shows a character. We observed aerial images by naked eyes as experiments. And we discuss the issues for practical application that the experiments have revealed.

(Keynote) Colloidal Quantum Shells: An Emerging Class of 2D Semiconductors

Low-dimensional colloidal semiconductors are inexpensive to process and offer a broad spectrum of attractive quantum-mechanical properties. The notorious problem of these nanostructures lies in their limited performance under high energetic loads, when more than one exciton per particle is created. Multiple excitons undergo fast Auger recombination, causing efficiently roll-off in energy-intensive applications, including high-brightness LEDs, X-ray scintillators, and solar cells. This presentation will discuss an emerging type of low-dimensional semiconductors, known as colloidal quantum shells that allow avoiding such multi-exciton (MX) energy losses. The geometry of quantum shells benefits from the spatial separation of multiple excitons, which leads to extraordinary improvements to MX lifetimes and MX quantum yield. We will compare quantum shells with other nanoscale geometries in three categories: Auger suppression, multi-exciton level structure, and solution-processed film conductivity, highlighting the potential benefits quantum shells can contribute to various applications. Theoretical analysis discussing the role of the quantum shell geometry in suppressing Auger recombination will also be presented.

Immersion Cooling of Suspended and Coated Nano-Phosphor Particles for Extending the Limits of Optical Extraction of Light Emitting Diodes

Abstract GaN LEDs are usually encapsulated with a cured phosphor-epoxy mixture for the light conversions from blue to white light. However, during this conversion, significant self-heating problems may occur due to insufficient cooling capabilities against the increasing power demand. Moreover, possible fracture and ultimate device failures were intersected with large displacements inside the LED package with these self-heating problems. Thus, including phosphor in a high brightness LED package is complex. Therefore, three coating technologies were investigated for an LED package's higher lifetime and ultimate optical output. Those are phosphor dispersed inside the liquid coolant as particles, remote phosphor-coated under the dome, and remote phosphor-coated under the dome with immersion cooling with dielectric liquid coolant. Their results were compared with the commonly used over chip coating application chosen as the baseline case in the current study. Furthermore, computational models and experimental studies were performed for proposed coating configurations. The chosen baseline case has shown higher junction temperatures, lower conversion efficiency, and undesirable color shifts at critical temperatures. As the first proposed technique, dispersed phosphor particles inside the dielectric liquid coolant have resulted with almost similar conversion efficiency but with a lower thermal enhancement on the LED junction than the baseline case. The second technique, remote phosphor system has resulted in better junction temperatures and 23% higher optical extraction than the baseline case. On the other hand, the remote phosphor with immersion cooling has shown the lowest junction temperature levels and extended the lumen extraction limits of white LEDs above 53% as the third proposed technique.

Indicator With Emergency Lighting Function Camping Lights

The motivation of this paper, when camping outdoors, we are afraid of running out of electricity, so we can generate electricity by hand-cranking. We use a small AC generator, high-capacity lithium-ion batteries, and high-brightness LED lights to make the control circuit, LED driver circuit, voltage regulator circuit, and USB charging and discharging circuit, and the brightness is adjustable in three steps. It can also be used as cell phone mobile power. Keywords: Emergency Lighting, LED, Camping light

On the Use of Class D Switching-Mode Power Amplifiers in Visible Light Communication Transmitters.

Visible Light Communication (VLC) is a wireless communication technology that uses visible light to transmit information. The most extended implementation of a VLC transmitter employs a DC-DC power converter that biases the High-Brightness LEDs (HB-LEDs), and a Linear Power Amplifier (LPA) that reproduces the communication signal. Unfortunately, the power efficiency of LPAs is very low, thus reducing the overall system efficiency and requiring huge cooling systems to extract the heat. In this work, the use of Class D Switching-Mode Power Amplifiers (SMPAs) is explored in order to overcome that limitation. It is important to note that this SMPA is widely used for different applications, such as audio and RF power amplifiers. Therefore, there are a lot of versions of a Class D SMPA depending on the topology used for the implementation and the modulation strategy used to control the switches. Hence, this work aims to identify, adapt and explain in detail the best approach for implementing a Class D SMPA for VLC. In order to validate the proposed idea, a power-efficient VLC transmitter intended for short-range and low-speed applications was built and evaluated.

High-Efficiency Flicker-Free LED Driver with Soft-Switching Feature.

A novel interleaved DC-DC buck converter is proposed to drive high-brightness light-emitting diodes (LEDs). The circuit configuration mainly consists of two buck converters, which are connected in parallel and use interleaved operation. Through interleaved operation, the power capability of the converter is doubled. Traditionally, two individual inductors are used in the two buck converters. The difference between conventional parallel-operated buck converters using two energy storage inductors and the proposed circuit is that the proposed circuit uses two small inductors and a coupled inductor that replace the two inductors of the buck converters. In this way, both buck converters can be designed to operate in discontinuous-current mode (DCM), even if the magnetizing inductance of the coupled inductor is large. Therefore, the freewheeling diodes can achieve zero-current switching off (ZCS). Applying the principle of conservation of magnetic flux, the magnetizing current is converted between the two windings of the coupled inductor. Because nearly constant magnetizing current continuously flows into the output, the output voltage ripple can be effectively reduced without the use of large-value electrolytic capacitors. In addition, each winding current can drop from positive to negative, and this reverse current can discharge the parasitic capacitor of the active switch to zero volts. In this way, the active switches can operate at zero-voltage switching on (ZVS), leading to low switching losses. A 180 W prototype LED driver was built and tested. Our experimental results show satisfactory performance.

High-Brightness Perovskite Microcrystalline Light-Emitting Diodes.

Here a high-brightness perovskite microcrystalline light-emitting diode (LED) is reported, in which the perovskite microcrystals were grown directly on the conductive substrate and a simple metal-insulator-semiconductor structure was adopted. A peak external quantum efficiency of 0.46% was obtained, which is high for perovskite microcrystalline LEDs. Importantly, the maximum luminance of the device reaches 8848.4 cd m-2, indicating an ultrahigh brightness of >1.2 × 106 cd m-2 for the microcrystals (corresponding to an ultrahigh current density of 80.9 A cm-2), because the light-emitting area of the microcrystals accounts for only ∼0.7% of the device area. In addition, we have studied the degradation of the device at a high current density by in situ microscopic observation and found that a severe Joule heating effect at large injection is the primary problem to be solved to realize electrically pumped perovskite microcrystal lasing.

High-brightness all-polymer stretchable LED with charge-trapping dilution.

Next-generation light-emitting displays on skin should be soft, stretchable and bright1-7. Previously reported stretchable light-emitting devices were mostly basedon inorganic nanomaterials, such as light-emitting capacitors, quantum dots or perovskites6-11. They either require high operating voltage or have limited stretchability and brightness, resolution or robustness under strain. On the other hand, intrinsically stretchable polymer materials hold the promise of good strain tolerance12,13. However, realizing high brightness remains a grand challenge for intrinsically stretchable light-emitting diodes. Here we report a material design strategy and fabrication processes to achieve stretchable all-polymer-based light-emitting diodes with high brightness (about 7,450 candela per square metre), current efficiency (about 5.3 candela per ampere) and stretchability (about 100per cent strain). We fabricate stretchable all-polymer light-emitting diodes coloured red, green and blue, achieving both on-skin wireless powering and real-time displaying of pulse signals. This work signifies a considerable advancement towards high-performance stretchable displays.

Lambertian Luminous Intensity Radiation Pattern Analysis in OLOS Indoor Propagation for Better Connectivity

This paper illustrates the impact of wavelength on the Optical Line of sight (OLOS) link working in the Visible Light Communication (VLC) spectrum. The extension of work is based on previous outcomes given by researchers. It has been elaborated with different determinants based on the color factor of LED available in the Visible Light (VL) spectrum. In the modern world, Light Emitting Diodes (LEDs) are prevailing the market as a light source, which is dominantly used at homes and workplaces. The designed VLC system includes LED as a transmitter, which is used as a higher source of brightness and provides both illuminations and data communication. Solid-state lighting characteristic shows the electroluminance capability of high brightness LEDs. Within few years, the luminous efficacy of LED is exponentially increasing from the range of less than 0.1 lm/W to over 230 lm/W with a huge lifetime of around 100,000 h. MATLAB is used to simulate a VLC link between LEDs (operated at different wavelengths) and photodetector. We present here the performance analysis of Lambertian Luminous Intensity radiation pattern (LLIRP) generated by different colors of LED for a clear OLOS model with different Spectral Luminous Efficiency at photonic vision. A designed system model of VLC supports short links present in indoor room conditions with better connectivity.

High brightness and stability pure-blue perovskite light-emitting diodes based on a novel structural quantum-dot film

The further development of perovskite light-emitting diodes (PeLEDs) is severely retarded by poor stability and low brightness of pure-blue emission in the range of 460–470 nm wavelength. Here, we devise a novel structure sandwich panel (SWP) of perovskite quantum dot (QD) film to modulate charge recombination, in which this structure is the first time to be used in LEDs. The SWP film is constructed by inserting a ZnCl2 ultrathin interlayer into the middle of pure-blue emitting (460 nm wavelength) CsPbBr3 QD film. The charge recombination zone is completely limited within the SWP film by the interlayer to alleviate the accumulation of carriers at interfaces of the QD film and hole transport layer, thus reducing the interfacial exciton quenching and Auger recombination. The PeLEDs based on SWP film show stabilized pure-blue emitting at 469 nm and external quantum efficiency (EQE) of 5% that shows low roll-off and maintains over 90% of the initial value at high luminance 10,000 cd m−2. The maximum luminance of the device is up to 10,410 cd m−2, which is the highest value for pure-blue PeLED reported, meeting the requirement of brightness in pixel for the augmented displays. The operational half-lifetime under continuous operation at the initial luminance of 100 cd m−2 is 59 h, which is the best operational stability for the known blue PeLEDs.

High-brightness Yellow Light-emitting Diode in A Single Ga-doped ZnO∶Ga Microwire Heterojunction

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Raspberry Pi-based Virtual Reality Headset for Cyclist Services

Following the development of technology and people's pursuit of a better life, MR technology has been applied in more and more scenarios. Based on the current research status, this project proposes to design a MR headset for cyclists. The helmet is developed based on Raspberry Pi, equipped with heat dissipation function, HD camera, and infrared camera are selected as sensing devices, HD camera is enabled in good light conditions, and the infrared camera is enabled in bad light conditions. The rider can observe the road conditions and outside information through the camera displayed in MR glasses in real-time. In addition to the live camera screen display, it can also display the time, memo information, and other functions. The map screen can be called up to show real-time navigation information. In addition, the helmet has built-in small Bluetooth audio. It can be connected to the phone via Bluetooth. The helmet is equipped with a total of three high-brightness LED light strips installed on the front and rear side of the helmet, which can be controlled by a button to make the light strip achieve the function of the turn signal. The gyroscope is installed in the button box of the light belt control. After detecting a fall, the buzzer and LED lights will go into alarm mode, which can improve the safety of the user's ride.

(Ce, Gd):YAG-Al2O3 composite ceramics for high-brightness yellow light-emitting diode applications

(Ce,Gd):YAG-Al2O3 composite ceramics were prepared for high-brightness yellow LED (565−590 nm) applications. Phase fraction, microstructure, thermal quenching effect, and luminescent properties of composite ceramics with varying compositions were studied in detail. Collaborating composite ceramics with InGaN blue chips, the relationship between thermal conductivity, temperature rise during LED-driven phosphor conversion, and steady-state luminous efficiency were elucidated. As the proportion of Al2O3 increases from 0 to 40 wt%, the steady-state luminous efficiency of yellow LED is enhanced from 100.88–109.49 lm W−1, benefiting from the increased thermal stability and reduced operating temperature of ceramics (from 141.1–132.2 °C). Additionally, scattering behavior and extraction efficiency of composite ceramics with different thicknesses were investigated.

Flexible High‐Stability Self‐Variable‐Voltage Monolithic Integrated System Achieved by High‐Brightness LED for Information Transmission (Small 45/2021)

Light Information Transmission A high performance self-variable-voltage light information transmission integrated system is reported in article number 2105207 by Jing Ning, Jincheng Zhang, and co-workers and its application potential in low-power, self-powered optical communication transmission systems is demonstrated. The diffusion adsorption regulation growth method and laser induction technology are proposed to realize high-brightness LED and flexible micro-supercapacitor on graphene. This study will provide a new approach to realize low-power optical communication transmission systems.

A single‐stage bridgeless LLC resonant converter with constant frequency control based LED driver

In this article, a single-stage bridgeless LLC resonant converter with a constant frequency control method is proposed for a high-brightness light-emitting diode (LED) driver. LED strings require drivers with high power density and high efficiency. This article presents a novel LED driver circuit topology based on switch integration and the switching controlled capacitor (SCC) technique. By combining the merits of a totem-pole bridgeless boost PFC unit and a high frequency SCC-LLC half-bridge resonant converter, the proposed topology can achieve high efficiency. Due to the SCC-LLC circuit topology structure, constant frequency control of the LLC resonant converter is achieved by the regulation of the equivalent resonant capacitance. The proposed novel LED driver topology can automatically achieve soft-switching characteristics and a high power factor. The operating principle of different operation modes and the characteristics of the proposed LED driver are analysed in detail. Finally, to demonstrate the feature of the proposed topology, a 100 W/70 V laboratory prototype is built. The satisfactory experimental results correspond with the theoretical analysis and parameter design.