Light-emitting Diode Module Research Articles

Influence and compensation of autocorrelation terms in depth-resolved spectroscopic Fourier-domain optical coherence tomography

We demonstrate depth-resolved spectral absorption measurements in the wavelength range from 750 to 850 nm using a broadband light source consisting of three spectrally shifted superluminescent light-emitting diode modules and a low-cost spectrometer-based Fourier-domain optical coherence tomography system. We present the theoretical model and experimental verification of interferences between autocorrelation terms and the signal carrying cross-correlation terms, strongly affecting the absorption measurements. A simple background subtraction, minimizing the artifacts caused by the interferences of autocorrelation and cross-correlation terms, is presented.

Application of GaN-based ultraviolet-C light emitting diodes – UV LEDs – for water disinfection

GaN-based ultraviolet-C (UV–C) light emitting diodes (LEDs) are of great interest for water disinfection. They offer significant advantages compared to conventional mercury lamps due to their compact form factor, low power requirements, high efficiency, non-toxicity, and overall robustness. However, despite the significant progress in the performance of semiconductor based UV LEDs that has been achieved in recent years, these devices still suffer from low emission power and relatively short lifetimes. Even the best UV LEDs exhibit external quantum efficiencies of only 1–2%.The objective of this study was to investigate the suitability of GaN-based UV LEDs for water disinfection. The investigation included the evaluation of the performance characteristics of UV LEDs at different operating conditions as well as the design of a UV LED module in view of the requirements for water treatment applications. Bioanalytical testing was conducted using Bacillus subtilis spores as test organism and UV LED modules with emission wavelengths of 269 nm and 282 nm.The results demonstrate the functionality of the developed UV LED disinfection modules. GaN-based UV LEDs effectively inactivated B. subtilis spores during static and flow-through tests applying varying water qualities. The 269 nm LEDs reached a higher level of inactivation than the 282 nm LEDs for the same applied fluence. The lower inactivation achieved by the 282 nm LEDs was compensated by their higher photon flux. First flow-through tests indicate a linear correlation between inactivation and fluence, demonstrating a well designed flow-through reactor. With improved light output and reduced costs, GaN-based UV LEDs can provide a promising alternative for decentralised and mobile water disinfection systems.

Reliability of High-Power Light Emitting Diode Attached With Different Thermal Interface Materials

As a solid electroluminescent source, white light emitting diode (LED) has entered a practical stage and become an alternative to replace incandescent and fluorescent light sources. However, due to the increasing integration and miniaturization of LED chips, heat flux inside the chip is also increasing, which puts the packaging into the position to meet higher requirements of heat dissipation. In this study, a new interconnection material—nanosilver paste is used for the LED chip packaging to pursue a better optical performance, since high thermal conductivity of this material can help improve the efficiency of heat dissipation for the LED chip. The bonding ability of this new die-attach material is evaluated by their bonding strength. Moreover, high-power LED modules connected with nanosilver paste, Sn3Ag0.5Cu solder, and silver epoxy are aged under hygrothermal aging and temperature cycling tests. The performances of these LED modules are tested at different aging time. The results show that LED modules sintered with nanosilver paste have the best performance and stability.

Effects of Moist Environments on LED Module Reliability

Unless their reliability is no longer a concern, light-emitting diodes (LEDs) will be unable to be used for broader applications. One important factor in the operating environment of LEDs is moisture, which is always present if the packaging is not hermetically sealed. In order to investigate the effects of moisture on the reliability of LEDs, several high-power white LEDs were subjected to extremely moist conditions at different temperature points in this study. Different light-output regression rates were measured. Digital microscopy was used to observe moisture diffusion on the LED module. The results demonstrate that the light output of LEDs decreases as the environmental moisture changes. Moisture diffuses into the interfaces of the packaging material, which not only decreases light output but may also disable the LED module due to electronic failure.

Plant experiments with light-emitting diode module in Svet space greenhouse

Light is necessary for photosynthesis and shoot orientation in the space plant growth facilities. Light modules (LM) must provide sufficient photosynthetic photon flux for optimal efficiency of photosynthetic processes and also meet the constraints for power, volume and mass. A new LM for Svet space greenhouse using Cree® XLamp® 7090 XR light-emitting diodes (LEDs) was developed. Monochromic LEDs emitting in the red, green, and blue regions of the spectrum were used. The LED-LM contains 36 LED spots – 30 LED spots with one red, green and blue LED and 6 LED spots with three red LEDs. Digital Multiplex Control Unit controls the LED spots and can set 231 levels of light intensity thus achieving Photosynthetic Photon Flux Density (PPFD) in the range 0–400 μmol m −2 s −1 and different percentages of the red, green and blue light, depending on the experimental objectives. Two one-month experiments with plants – lettuce and radicchio were carried out at 400 μmol m −2 s −1 PPFD (high light – HL) and 220 μmol m −2 s −1 PPFD (low light – LL) and 70% red, 20% green and 10% blue light composition. To evaluate the efficiency of photosynthesis, in vivo modulated chlorophyll fluorescence was measured by Pulse Amplitude Modulation (PAM) fluorometer on leaf discs and the following parameters: effective quantum yield of Photosystem II ( Φ PSII) and non-photochemical quenching (NPQ) were calculated. Both lettuce and radicchio plants grown at LL express higher photochemical activity of Photosystem II (PSII) than HL grown plants, evaluated by Φ PSII. Accelerated rise in NPQ in both LL grown plants was observed, while steady state NPQ values were higher in LL grown lettuce plants and did not differ in LL and HL grown radicchio plants. The extent of photoinhibition process in both plants was evaluated by changes in malonedialdehyde (MDA) concentration, peroxidase (POX) activity and hydrogen peroxide (H 2O 2) content. Accumulation of high levels of MDA and increased POX activity correlating with decreased H 2O 2 content were observed in both HL grown plants. These biochemical indicators revealed higher sensitivity to photodamage in HL grown lettuce and radicchio plants. LL conditions resulted in more effective functioning of PSII than HL when lettuce and radicchio plants were grown at 70% red, 20% green and 10% blue light composition.

Micropatterned single lens for wide-angle light-emitting diodes

This work presents a simple and effective method for a wide-angle light-emitting diode module by using a single lens corrugated with micropattern arrays. Impinged onto the micropattern arrays of a curved surface, light undergoes an enhancement of the illumination angle due to omnidirectional diffraction. A hemispherical dome lens with micropattern arrays is microfabricated by a reconfigurable microtemplating and a replica molding method. Depending on the micropattern size, the experimental and simulation results show the micropatterned single lens has the wide illumination angle as well as the high extraction efficiency of an incoming LED light source, compared with a conventional dome lens.

Fabrication and thermal optimization of LED solar cell simulator

This paper describes fabrication and characterization of a solar simulator which utilizes light emitting diode (LED) as a lighting source. A solar cell powered by the LED simulator with 0.9 sun exhibited about 80% of the output power generated by the conventional Xenon lamp simulator with 1 sun. Measured temperatures for the surface of lens and fin of heat sink were in good agreement with the calculated values. Detailed thermal performance of the LED lighting was projected using a computational fluid dynamics (CFD) method for the various design parameters such as layout of the LED package and number of fins of the heat sink. It was demonstrated that the junction temperature of the LED module can be significantly decreased by optimization of the parameters.

Si-based packaging platform for LED module using electroplating method

A method for fabricating a Si-based packaging platform with a reflector and electrode-guided interconnections is proposed for the packaging component of a high-power light-emitting diode (LED) module. The reflector is fabricated by Ni/Au/Ag-electroplating which is patterned by SU-8 2075 and 4620 negative photo-resistors and the electrical interconnections are formed by Cu/Au-electroplating in the same body. The heat generated by the LED chip is dissipated directly to the Si body through the large metal-plated platform. This method is suitable for high-efficiency and low-cost LED packaging.

Enhanced Lateral Heat Dissipation and Reduced Wavelength Shift of AlGaInP/GaAs Light Emitting Diodes by Electroplating

We compare the device performance of a conventional light emitting diode (LED) module with that of an LED module after electroplating a lateral heat dissipation (LHD) structure along the sidewalls of the chip. At 350 mA, the luminous intensity of the proposed LED was enhanced by 207%. At the same current, the dominant and peak wavelength shifts of the LED exhibited a better performance of 2.1 and 4.4 nm, respectively, compared with the conventional performance of 7.2 and 23 nm. These results indicate that the LED with the LHD structure is useful in improving the performance by enabling greater heat dissipation.

Effects of Defects on the Thermal and Optical Performance of High-Brightness Light-Emitting Diodes

Defects in terms of voids, cracks, and delaminations are often generated in light-emitting diodes (LEDs) devices and modules. During various manufacturing processes, accelerated testing, inappropriate handling, and field applications, defects are most frequently induced in the early stage of process development. One loading is due to the nonuniform loads caused by temperature, moisture, and their gradients. In this research, defects in various cases are modeled by a nonlinear finite-element method (FEM) to investigate the existence of interfaces, interfacial open and contacts in terms of thermal contact resistance, stress force nonlinearity, and optical discontinuity, in order to analyze their effects on the LED's thermal and optical performance. The simulation results show that voids and delaminations in the die attachment would enhance the thermal resistance greatly and decrease the LED's light extraction efficiency, depending on the defects' sizes and locations generated in packaging.

Temperature estimation of high-power light emitting diode street lamp by a multi-chip analytical solution

Light emitting diodes (LEDs) are now widely used in many fields including traffic lights, vehicle backlights and liquid crystal display (LCD) displays because of their long life, good illumination efficiency and low energy consumption. At present, LEDs are increasingly replacing the traditional lighting and are being used in general illumination such as the street lamp. For the high-power LED street lamps, good light extraction is the most important thing, but low junction temperature of the LED modules is also critical for achieving a long lifetime and a high optical efficiency. Actually, there have been many reports about early failures of street lamps, called dead lamps that have been regarded as a barrier in the public and administration acceptance of LED street lamps. Therefore temperature estimation is always a crucial issue for LED product development. A multi-chip spreading thermal resistance model was applied to estimate the temperature distribution of LED street lamp. The experiment was first done to obtain temperatures of several locations in a prototype LED street lamp. Then the multi-chip spreading resistance model was established to calculate the full temperature distribution. Comparison between the model calculation and experimental measurement showed a good agreement, which demonstrates that the present model can be used in engineering design to estimate the temperature distribution of high-power LED street lamps.

An Optimum Design and Fabrication of Focus Lens for High Intensity Light-Emitting Diodes

A maximum output intensity of high-power light-emitting diodes (LEDs) with high-efficiency focus lens is demonstrated. A commercial software package of Trace Pro and one-factor method are used to simulate the focus lens. The optimum parameters of focus-lens design are the radius curvature, cavity depth, and lens height are 2.75, 2.45, and 5.7 mm, respectively. For the fabrication of focus lens with injection molding, the optimum parameters are simulated by adapting Taguchi's method of the smaller-the better algorithm in a software package for Moldex 3D. By employing both optimum design and fabrication of the focus lens, a maximum peak intensity for 64.6 cd for a 1 W blue LED module was realized under a constant driving current of 320 mA and the voltage of 3.2 V. In comparison with a commercial focus lens used in high-power LEDs under the same test conditions, the high-power LEDs with proposed focus lens exhibits about 2–3 times improvement in the output intensity. This study may provide a practical guideline for design and fabrication of a high-efficiency focus lens used in high-intensity high-power LED modules.

High-Power, Computer-Controlled, Light-Emitting Diode–Based Light Sources for Fluorescence Imaging and Image-Guided Surgery

Optical imaging requires appropriate light sources. For image-guided surgery, in particular fluorescence-guided surgery, a high fluence rate, a long working distance, computer control, and precise control of wavelength are required. In this article, we describe the development of light-emitting diode (LED)-based light sources that meet these criteria. These light sources are enabled by a compact LED module that includes an integrated linear driver, heat dissipation technology, and real-time temperature monitoring. Measuring only 27 mm wide by 29 mm high and weighing only 14.7 g, each module provides up to 6,500 lx of white (400-650 nm) light and up to 157 mW of filtered fluorescence excitation light while maintaining an operating temperature < or = 50 degrees C. We also describe software that can be used to design multimodule light housings and an embedded processor that permits computer control and temperature monitoring. With these tools, we constructed a 76-module, sterilizable, three-wavelength surgical light source capable of providing up to 40,000 lx of white light, 4.0 mW/cm2 of 670 nm near-infrared (NIR) fluorescence excitation light, and 14.0 mW/cm2 of 760 nm NIR fluorescence excitation light over a 15 cm diameter field of view. Using this light source, we demonstrated NIR fluorescence-guided surgery in a large-animal model.

Development of street lighting system-based novel high-brightness LED modules

The development of high-power light emitting diode (LED) for street lighting is growing continuously owing to its greater energy efficiency, long operating life and light control. Users of street lighting are compelled to adopt this technology over traditional light sources. An alternative solution based on a novel 9LEDM (9-LED module) and adaptive driver is shown. The design of the 9LEDM is derived from the thermal, photometric, power electronics techniques to meet the application of street lighting. The 9LEDM performances with a price less than 1$/Watt (W) and luminous flux higher than 110 Lumens (Lm)/W compared with traditional ones. Furthermore, several restrictions of driving the solid-state lighting loads are overcome by an adaptive street lighting driver with an AC/DC converter of a quasi-resonant operation flyback topology and with Soft Startup, Full ON, Half ON functions by sensing the ambient light and working temperature. Finally, a high performance/cost 50 W pole head as a design example is conducted to illustrate the complete design process, and the results from the demonstration projection with two pole heads of 50 W for a 12 m pole show a luminous intensity range from 38 to 19 lux with a heat sink temperature of 58degC and an energy saving more by 72% compared with conventional street lighting after three months of running.

A Novel Two-Dimensional Adaptive Dimming Technique of X-Y Channel Drivers for LED Backlight System in LCD TVs

In this paper, a novel two-dimensional (2-D) adaptive dimming technique with X-Y channels for light-emitting diode (LED) backlight system in LCD TVs is proposed. The proposed LED backlight has matrix-structured LED modules with row and column switches to control the brightness of individual division block. It shows local dimming effects such as reduced power consumption and high dynamic contrast ratio even with much less number of LED drivers than that of the conventional 2-D local dimming method. Therefore, low cost and compact design of LED drivers can be achieved. This paper also contains a new adaptive dimming algorithm and image manipulation technique for the proposed LED backlight system. The proposed dimming technique is verified by simulation and experimental results based on a RGB-LED backlight of a 32-in LCD TV.

백색 LED 조명의 색온도에 관한 감성평가

The aim of this study is to investigate the sensitivity evaluation of human beings in reacting to the correlated color temperature of the optical properties of white LED lighting. For the sake of this study, white light-emitting diode modules have been fabricated their correlated color temperature have been measured, test cabinets for the sensitivity evaluation have been constructed with the white LED modules, and their sensitivity reactions on the test cabinets have been evaluated and analyzed. The sensitivity reaction has been evaluated by the semantic differential method with 15 selected questions, and the reliability and the content validity of their lighting have been analyzed to 3 factors which foe the activity as the first factor, the stability as the second one, the potency as the third one, respectively. For the data analysis on the sensitivity reaction, the dependent variable is the score of the sensitivity evaluation and the independent one is the correlated color temperature of the test module. The results of this study is as follows: In the case of the sensitive evaluation on the activity and the potency in the white LED lighting compared with the fluorescent lamp, the subjects have made higher mark on with 8,300[K], and in the factor of the stability, they have made higher mark on with 3,800[K].

Failure Mechanisms Associated With Lens Shape of High-Power LED Modules in Aging Test

High-power light-emitting diode (LED) modules encapsulated with different lens shapes after a thermal-aging test were studied experimentally and numerically. Samples from different manufacturers were aged at 80degC, 100degC, and 120degC under a constant driving voltage of 3.2 V. The results showed that the LED modules encapsulated with a hemispherical-shaped plastic lens exhibited a better lifetime due to better thermal dissipation than those with cylindrical-or elliptical-shaped plastic lenses. Results also showed that the optical power of the LED modules increased after removing the plastic lens because degradation of the lens material decreased the amount of light. The key module package-related failure modes under thermal-aging were identified as the degradation of the plastic lens and lens material. A finite-element method (FEM) simulation showed that thermal and major principle stress distributions of the high-power LED modules were dependent on aging temperature. Both experimental and FEM simulated results clearly indicated that a uniformly thermal dissipation to minimize the thermal effect along the thermal path from the LED chip to the plastic lens is essential to extend the operating life of high-power LED modules.

Unsupervised Fluorescence Lifetime Imaging Microscopy for High Content and High Throughput Screening

Proteomics and cellomics clearly benefit from the molecular insights in cellular biochemical events that can be obtained by advanced quantitative microscopy techniques like fluorescence lifetime imaging microscopy and Förster resonance energy transfer imaging. The spectroscopic information detected at the molecular level can be combined with cellular morphological estimators, the analysis of cellular localization, and the identification of molecular or cellular subpopulations. This allows the creation of powerful assays to gain a detailed understanding of the molecular mechanisms underlying spatiotemporal cellular responses to chemical and physical stimuli. This work demonstrates that the high content offered by these techniques can be combined with the high throughput levels offered by automation of a fluorescence lifetime imaging microscope setup capable of unsupervised operation and image analysis. Systems and software dedicated to image cytometry for analysis and sorting represent important emerging tools for the field of proteomics, interactomics, and cellomics. These techniques could soon become readily available both to academia and the drug screening community by the application of new all-solid-state technologies that may results in cost-effective turnkey systems. Here the application of this screening technique to the investigation of intracellular ubiquitination levels of alpha-synuclein and its familial mutations that are causative for Parkinson disease is shown. The finding of statistically lower ubiquitination of the mutant alpha-synuclein forms supports a role for this modification in the mechanism of pathological protein aggregation.

GaN-Based Power LEDs With CMOS ESD Protection Circuits

A power light-emitting diode (LED) module has been successfully designed and demonstrated by combining GaN-based power LEDs with CMOS electrostatic discharge (ESD) protection circuits through a flip-chip process. It was found that we could enhance the power LED output intensity by 20% by using the flip-chip technology. Lifetimes of flip-chip power LEDs were also found to be better. It was also found that the use of CMOS ESD protection circuits did not degrade the output intensity and lifetime of flip-chip power LEDs. Furthermore, it was found that we could not only significantly enhance the reverse ESD characteristics but could also enhance the positive ESD characteristics of nitride-based LEDs by using the CMOS ESD protection circuits.

2318 LEDモジュールの放熱実装技術(要旨講演,情報機器コンピュータメカニクス)

We developed a light source module using a high-power light emitting diode (LED). Production of long life LED chips requires the thermal resistance of its LED module to be reduced. We analyzed thermal conductivity in an electrically conductive adhesive used in a LED module. Results confirmed that the thermal conductivity of an electrically conductive adhesive, including contact thermal resistance, is important when analyzing thermal conduction in a LED module.