LED Light Output Research Articles

Chip-level mass detection for micro-LED displays based on regression analysis and deep learning.

Though micro-light-emitting diode (micro-LED) displays are regarded as the next-generation emerging display technology, challenges such as defects in LED's light output power and radiation patterns are critical to the commercialization success. Here we propose an electroluminescence mass detection method to examine the light output quality from the on-wafer LED arrays before they are transferred to the display substrate. The mass detection method consists of two stages. In the first stage, the luminescent image is captured by a camera by mounting an ITO (indium-tin oxide) transparent conducting glass on the LED wafer. Due to the resistance of the ITO contact pads and on-wafer n-type electrodes, we develop a calibration method based on the circuit model to predict the current flow on each LED. The light output power of each device is thus calibrated back by multi-variable regression analysis. The analysis results in an average variation as low as 6.89% for devices predicted from luminescent image capturing and actual optical power measurement. We also examine the defective or non-uniform micro-LED radiation profiles by constructing a 2-D convolutional neural network (CNN) model. The optimized model is determined among three different approaches. The CNN model can recognize 99.45% functioning LEDs, and show a precision of 96.29% for correctly predicting good devices.

An Experimental Investigation on the Role of LEDs on the Lifetime Performance of Consumer LED Luminaires

Solid-state lighting technology currently dominates illumination technologies, which have been growing throughout time. LEDs are a semiconductor-based illumination solution that is energy-efficient, long-lasting, and capable of meeting all application requirements for quantity of light, colour and spatial limitations. In all of the essential lighting applications, LED reliability and lifetime performance are critical. The LED luminaire’s performance may decline over time, resulting in lower light output or different colours than the required colour characteristics. The importance of LED performances in LED luminaires as a system has only lately been realised. Different LEDs are used in two commercially available LED luminaires with exact electrical and optical specifications that are exposed to accelerated working conditions. The paper outlines a method for analysing and forecasting lifetime based on lumen maintenance for light output, Duv for colour-based quantification. The xy chromaticity, spectral power distribution, and SEM-EDS analysis are used to detect the characteristics indicative of variations in LED light output performance with degradation. The findings imply that LED packaging and device physics are important factors in the LED luminaire’s overall lifetime performance. The work gives consumers the opportunity to see specifics about luminosity and colour-based changes as a product data-sheet, making it easier for them to choose appropriate luminaires for their needs. It also aids LED and LED luminaire makers in making appropriate design and technological adjustments, resulting in improved LED performance that is longlasting and consistent in colour stability.

Experımental and Numerıcal Analysis of the Effect of Components on a Double-Sided PCB on LED Junction Temperature and Light Output Using CFD

In today’s lighting industry, with developing technology and a widened usage area, LEDs have become very popular due to their higher energy efficiency and longer life. In the present study, the effect of electronic components on printed circuits and the radiation level on light output was studied. The performed analysis was validated with an experimental method. For the finite volume method, FloEFD 2019, commercial software, was used. The ambient temperature was assumed to be 23 °C. The value of solar irradiance was taken as 1009 W/cm2. LEDs on a PCB were driven at 70 mA at first and then at 50 mA, and, by exerting power on all electronic components, analyses were performed. Both sides of the PCB were examined, and, in order to achieve efficient heat conduction, the power and distribution of the electronic components on the back side of the LEDs were optimized. With a new electronic circuit design, analyses were performed at 50, 55, 60, 65, and 70 mA. It was determined that the highest light output was achieved at 65 mA and that the distribution of electronic components on a PCB indirectly affects light output through junction temperature (Tj).

Effect of double-layer phosphor coating on LED light output of COB encapsulation

Effect of double-layer phosphor coating on LED light output of COB encapsulation

Power consumption control of LEDs considering their specific characteristics and ambient temperature variations

Ambient temperature is one of the factors affecting the luminous flux and the lifetime of LEDs. To consider this factor, In this study, the design and implementation of an innovative power control system of LEDs is presented. The distinct feature of the proposed system is its ability to use the information of the ambient temperature and the specific characteristic curves of LEDs. In the proposed method, a microcontroller unit controls the input power of the LED chipsets just by using the instant measured ambient temperature data, if the instant power is higher than the standard power (at 25 °C). The introduced system adjusts the input power and the light output of LEDs at temperatures below the standard ambient temperature of 25 °C. At the same time, this system preserves the standard lighting levels unchanged. Results of the calculations and implementation of the proposed system verify the efficiency of the developed method.

Improved emission intensity of UVC-LEDs from using strain relaxation layer on sputter-annealed AlN

This paper presents the effects of Mg concentration in a Mg-doped aluminum nitride (AlN) strain relaxation layer according to the metalorganic vapor-phase epitaxy method. A UV LED using a Mg-doped AlN strain relaxation layer at a Mg concentration of 3 × 1020 cm−3 on a sputter-annealed AlN template produced light output power 11 times as high as that with conventional LED structures. The AlGaN-on-AlN relaxation rate and LED light output power increased starting from Mg concentrations of 1019 cm−3. These characteristics had almost the same values when the Mg concentration was less than 3 × 1019 cm−3. These results show the improvement of efficiency caused by void formation due to the inversion domain.

P‐9.10: Design and Fabrication of Micro‐lens Array Based on Micro‐LED Projector

LEDoS(Light Emitting Diode on Silicon) is developing rapidly as a new type of projection technology compared with DLP(Digital Light Processing) and LCoS(Liquid Crystal on Silicon). In addition, Micro‐LED is playing an important role in display and lighting areas because of its high display quality. Therefore, researching and designing a Micro‐LED based LEdoS has obvious advantages in brightness and color saturation, when used in projectors, it can not only completely eliminate the backlight, but also improve the LEE(Light extraction efficiency) by minimizing the optical components. This experiment aims to develop a Micro‐lens array that matches the LEDoS chip and combines the Micro‐lens array with the LEDoS chip to optimize the design by using Tracepro, including the material and shape of Micro‐lens. The Micro‐lens is used to optimize the LED pixels light output angle to reduce color mixing problems between adjacent LED pixels. At the same time the Micro‐lens can also improve the efficiency of LED light coupling, thereby further improving the LED light output efficiency.

The effect of capacitance on drive current of general lighting LED luminaires

The reliability of a LED luminaire depends on the reliability of each of its subsystems. Experience suggests that, of these subsystems, it is the LED driver that tends to fail earliest. Any LED driver has an electrolytic capacitor to limit the ripple current, which helps the luminaire to function appropriately. This paper describes the effects on ripple current of changes in the capacitance and thus on LED luminaire performance. A capacitor bank is developed containing electrolytic capacitor combinations to obtain 27 capacitance values in the range 0.017 to 1570 µF. Two commercially available LED downlighter luminaires of the same model and manufacturer were used for this study. The ripple current and lumen output values are observed after connecting each capacitance from the bank, and the percentage flicker is calculated. LED light output shows visible flicker for low capacitances up to 0.1 µF with percentage flicker above 100%, while percentage flicker for capacitors up to 100 µF is more than 50%. For capacitance values of 220 µF and more, the percentage flicker is less than 50%. For the LED driver the capacitor decides the amount of ripple in the output current, so this work helps in formulating metrics for determining the service life of LED luminaires.

무분극 a-plane 질화물계 발광다이오드에서 SiO2 전류 제한 층을 통한 발광 효율 증가

In this study, we investigate the <TEX>$SiO_2$</TEX> current blocking layer (CBL) to improve light output power efficiency in nonpolar a-plane (11-20) GaN LEDs on a r-plane sapphire substrate. The <TEX>$SiO_2$</TEX> CBL was produced under the p-pad layer using plasma enhanced chemical vapor deposition (PECVD). The results show that nonpolar GaN LED light output power with the <TEX>$SiO_2$</TEX> CBL is considerably enhanced compared without the <TEX>$SiO_2$</TEX> CBL. This can be attributed to reduced light absorption at the p-pad due to current blocking to the active layer by the <TEX>$SiO_2$</TEX> CBL.

Reducing the stroboscopic effects of LED luminaires with pulse width modulation control

Pulse width modulation for dimming the light output of LEDs has become common. When pulse width modulation is used at low frequencies unwanted visual artefacts including flicker perception and stroboscopic effects may occur. These artefacts need to be avoided or at least reduced to a minimum in order to obtain high user acceptance. In this paper, an optimized phase-shifted pulse width modulation method is described, implemented and validated in a visual experiment. The method is intended to minimize the stroboscopic effect on a reference surface by first optimizing the LED units of a single LED luminaire and then co-optimizing several of these luminaires. The optimized pulse width modulation waveforms are then compared to standard pulse width modulation dimming methods. In the visual experiment, 13 subjects rated the extent of the stroboscopic effect of standard and optimized waveforms in a white painted experimental room. The results indicate that the optimized waveforms are indistinguishable from constant light.

Effects of photodynamic therapy on Enterococcus faecalis biofilms.

Microbial biofilms are involved in almost all infectious pathologies of the oral cavity. This has led to the search for novel therapies specifically aimed at biofilm elimination. In this study, we used atomic force microscopy (AFM) to visualize injuries and to determine surface roughness, as well as confocal laser scanning microscopy (CLSM) to enumerate live and dead bacterial cells, to determine the effects of photodynamic therapy (PDT) on Enterococcus faecalis biofilms. The AFM images showed that PDT consisting of methylene blue and a 670-nm diode laser (output power 280 mW during 30 s) or toluidine blue and a 628-nm LED light (output power 1000 mW during 30 s) induced severe damage, including cell lysis, to E. faecalis biofilms, with the former also causing an important increase in surface roughness. These observations were confirmed by the increase in dead cells determined using CLSM. Our results highlight the potential of PDT as a promising method to achieve successful oral disinfection.

Strong Enhancement in Light Output of GaN-Based LEDs With Graded-Refractive-Index ITO Deposited on Textured V-Shaped Pits

Strong Enhancement in Light Output of GaN-Based LEDs With Graded-Refractive-Index ITO Deposited on Textured V-Shaped Pits

Influence of the temperature dependent spectral power distribution of light-emitting Diodes on the illuminance responsivity of a photometer

Accurate optical measurements of LEDs are crucial because of the increasing popularity of LEDs. However, a photometer with a V(λ) filter spectrum curve may yield large errors when it is used for photometric measurements of colored LEDs. The junction-dependent light output and spectral distribution of LEDs also introduce measurement errors of the measured photometric characteristics. For the accurate measurements of LEDs, the c(St,Ss) factors were used to estimate the possible deviation in the photometric measurement of colored LEDs with various junction temperatures using commercial and industrial grade photometer heads. The spectral measurements of LEDs with specified junction temperature were conducted using a miniature fiber-optic spectrometer, and the relative spectral power distributions of LEDs were used to calculate the spectral mismatch correction c(St,Ss) factors of the photometer heads. Therefore, the c(St,Ss) factors of colored LEDs were calculated according to the temperature dependent spectral power distributions with various junction temperatures, and these factors were used to estimate the possible deviation in the photometric measurement of colored LEDs. The estimation of the possible deviation in the photometric measurement shows that photometers with excellent relative spectral responsitivities must be used for accurate measurement; otherwise, careful calibration must be conducted when using a photometer with inferior relative spectral responsitivity of the photopic filter.

Studies and Applications of Advanced Laser Scribing for High Brightness LEDs

The optical and electrical properties of LEDs scribed using both traditional and advanced laser scribing were investigated. Variations in scribe line texture and depth were examined and monitored for both laser types using both optical and electron microscopy. Simulation was conducted and verified by the experimental results on laser scribing depth versus LED light output. The metrology techniques also correlated the sidewall roughness with light output of LED between traditional and advanced laser scribing. Improvements by the advanced laser scribing were demonstrated for different LED designs, such as DBR with metal mirrors. Our study showed that the advanced laser scribing is comparable to the sidewall etching process which is the current industrial standard. Our advanced laser scribing system can process different types of metal mirrors on top of DBR structures in a single tool solution. We also presented our latest results on the emerging new substrates of vertical LEDs on Si and other advanced non-sapphire substrates.

Effect of Packaging Materials and Process on the White LED Fabricated with Quantum Dots

In order to ensure long lifetime and stable light output of LEDs the thermal performance parameters need to be designed in the LED chip package and module level, which include such items as heat sink structure and materials, interface materials and substrates. In this work we used aluminium nitride(AlN) as submount of LED chips and made chip on board(COB) type LED module. The effect of different silver(Ag) epoxy bonding materials and bonding methods on the performance of LED module were examined. The effect of addition of red quantum dot(QD) on the performance of white LED was also studied.

Investigation of LED Light Output Performance Characteristics Under Different Alternating Current Regulation Modes

LED performance characteristics under dc regulation modes have been studied extensively. But limited literatures are dedicated to studies of LED performance characteristics under different ac regulation modes. With direct ac powering LEDs for lighting application being available and more attractive in efficiency due to the elimination of ac-dc converter, investigation of the influence of different ac current regulation modes on LED performance characteristics becomes important and essential. This paper presents an experimental investigation of different current regulation modes on LED light output with different LED connection configurations. It is found certain current regulation mode under which a higher light output with the same absolute average current can be obtained. The result is due to facts that the absolute average current is the measurement of electrons and holes recombination rate inside the LED, and second-order nonlinear effect and thermal issue lead to the different light output for different ac regulation modes.

Automatic diagnosis and control of distributed solid state lighting systems

This paper describes a new design concept of automatically diagnosing and compensating LED degradations in distributed solid state lighting (SSL) systems. A failed LED may significantly reduce the overall illumination level, and destroy the uniform illumination distribution achieved by a nominal system. To our knowledge, an automatic scheme to compensate LED degradations has not yet been seen in the literature, which requires a diagnostic step followed by control reconfigurations. The main challenge in diagnosing LED degradations lies in the usually unsatisfactory observability in a distributed SSL system, because the LED light output is usually not individually measured. In this work, we tackle this difficulty by using pulse width modulated (PWM) drive currents with a unique fundamental frequency assigned to each LED. Signal processing methods are applied in estimating the individual illumination flux of each LED. Statistical tests are developed to diagnose the degradation of LEDs. Duty cycle of the drive current signal to each LED is re-optimized once a fault is detected, in order to compensate the destruction of the uniform illumination pattern by the failed LED.

Enhanced Light Output of Vertical GaN-Based LEDs with Surface Roughened by SiO[sub 2] Nanotube Arrays

Enhanced Light Output of Vertical GaN-Based LEDs with Surface Roughened by SiO[sub 2] Nanotube Arrays

Light Outputs of LED with Various Refractive Indices and Geometrical Structures of Encapsulants

In this paper we present the results of experiments and simulations for the light output power from LEDs for various refractive indices and the geometrical structures of the LED encapsulants. InGaN-based LED chips were fabricated and were bonded in Ag reflector cups within polyphthalamide (PPA) chip carriers; then, encapsulants with various refractive indices and the geometrical structures were fabricated onto them by using a dispensing method. The light output power with the encapsulant was shown to increase with the refractive index of the encapsulant materials in the case of a spherical encapsulant while it decreased in the case of a flat geometry encapsulant. We performed ray tracing simulations for the LED light output and confirmed that the simulation results were consistent with our experimentally measured results. In addition, the light output with the encapsulant rapidly increased with the sidewall angle of the chip carrier in the case of the flat encapsulant while it was not aected by the sidewall angle, remaining constant, in the case of the spherical geometry.

Enhanced Light Output of AlGaInP LEDs Using Indium-Zinc Oxide Film as TCL and Electroplated Nickel Substrate

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