LED Module Research Articles

Estimation the Amount of Heat Generated by LEDs under Different Operating Conditions

LEDs are not 100 % efficient at converting input power to light. Some of the energy is converted into heat and must be transferred to the ambient. Two approaches are used to assess the amount of heat generated by the LED - based on the luminous efficacy of radiation and a new one presented in the paper. To provide sufficient accuracy in thermal evaluations closer to the real operating modes for a specific LED module a new technique is developed. The aim is to evaluate the amount of heat generated during design phase of LED lighting. Experiments of LED modules are conducted to evaluate LEDs efficiency at converting input power to heat. For the heat dissipation study and thermal analysis of LED module are used non-contact temperature measurement using an infrared camera combined with computer aided thermal modelling and simulation. DOI: http://dx.doi.org/10.5755/j01.eie.22.2.8522

Nighttime Supplemental LED Inter-lighting Improves Growth and Yield of Single-Truss Tomatoes by Enhancing Photosynthesis in Both Winter and Summer.

Greenhouses with sophisticated environmental control systems, or so-called plant factories with solar light, enable growers to achieve high yields of produce with desirable qualities. In a greenhouse crop with high planting density, low photosynthetic photon flux density (PPFD) at the lower leaves tends to limit plant growth, especially in the winter when the solar altitude and PPFD at the canopy are low and day length is shorter than in summer. Therefore, providing supplemental lighting to the lower canopy can increase year-round productivity. However, supplemental lighting can be expensive. In some places, the cost of electricity is lower at night, but the effect of using supplemental light at night has not yet been examined. In this study, we examined the effects of supplemental LED inter-lighting (LED inter-lighting hereafter) during the daytime or nighttime on photosynthesis, growth, and yield of single-truss tomato plants both in winter and summer. We used LED inter-lighting modules with combined red and blue light to illuminate lower leaves right after the first anthesis. The PPFD of this light was 165 μmol m-2 s-1 measured at 10 cm from the LED module. LED inter-lighting was provided from 4:00 am to 4:00 pm for the daytime treatments and from 10:00 pm to 10:00 am for the nighttime treatments. Plants exposed only to solar light were used as controls. Daytime LED inter-lighting increased the photosynthetic capacity of middle and lower canopy leaves, which significantly increased yield by 27% in winter; however, photosynthetic capacity and yield were not significantly increased during summer. Nighttime LED inter-lighting increased photosynthetic capacity in both winter and summer, and yield increased by 24% in winter and 12% in summer. In addition, nighttime LED inter-lighting in winter significantly increased the total soluble solids and ascorbic acid content of the tomato fruits, by 20 and 25%, respectively. Use of nighttime LED inter-lighting was also more cost-effective than daytime inter-lighting. Thus, nighttime LED inter-lighting can effectively improve tomato plant growth and yield with lower energy cost compared with daytime both in summer and winter.

Model Identification and Wall-Plug Efficiency Measurement of White LED Modules

In this study, an experimental method is developed to measure the Wall-Plug efficiency of white LED modules without using any apparatus or sensors to measure the intensity of light. The tested LED module consists of a white LED chip-on-board affixed on a heatsink. The proposed method is mainly based on thermal and electrical models of the LED module. Measurements of thermal and electrical power are implemented instead of optical power. The presented method is not intended to replace the existing conventional techniques used to obtain optical and thermal characteristics of LEDs, but it provides a simplified way to evaluate the Wall-Plug efficiency of white LED modules under pragmatic operational conditions. In this method, the parameters of the wall-plug efficiency model of an LED-heatsink module are identified. Then, the model is applied to evaluate the efficiency at operating conditions of different heatsink temperature and input current. A 9 W Cree© XLamp white LED was tested at an ambient temperature of 23°C±1. Experimental results revealed that the parameters of the efficiency model can be extracted using the proposed method without measurement of optical power.

레일 체결구 결함 검측 모듈의 방열성능 개선을 위한 열 해석

In this paper, various heat dissipation designs for a rail anchoring failure detection module were investigated by a thermal flow analysis. For the detection module with the heat dissipation design on the overall housing surface, an average temperature inside the module was lowered by when compared to no heat dissipation design. In addition, an internal heat-flow blocking layer and an heat conduction layer inserted between the LED module and housing case were effective in reducing the temperature in the rail anchoring failure detection, which has a limited space for installation and little air flow. Especially, the temperature near LED module decreased below when the optimal heat dissipation design was applied.

An experimental and analytical investigation of the photo-thermal-electro characteristics of a high power InGaN LED module

The photo-thermal-electro characteristics of a high power InGaN LED module were studied both experimentally and theoretically. Three types of heat sink substrate composed of two layers of materials were used to investigate the coupled relationships between chip temperature, thermal resistance, input electric power and light emission efficiency. The results showed that the thermal spreading resistance accounts for a significant fraction of the total substrate thermal resistance. The measured thermal resistance of the LED module increased with rising electric power input. Luminescent efficacy measurements revealed that this increase of thermal resistance was the result of increased heat dissipation from the chip due to less efficient conversion of electric power to light output. Furthermore, experimental results showed that the radiant efficiency of the LED decreases with increasing input electric power. The coupled effects of chip temperature, input power and thermal resistance of the substrate are responsible for this efficiency droop. A revised model for estimating the luminous efficacy that takes both thermal and electrical effects into consideration is proposed. It is shown that the efficiency droop of the LED module for all three types of substrates can be clearly demonstrated by using the proposed analysis.

Heat Transfer Characteristics in High Power LED Packaging

This study uses the T3Ster transient thermal resistance measuring device to investigate the effects to heat transfer performances from different LED crystal grains, packaging methods and heat-sink substrates through the experimental method. The experimental parameters are six different types of LED modules that are made alternatively with the crystal grain structure, the die attach method and the carrying substrate. The crystal grain structure includes the lateral type, flip chip type and vertical type. The die attach method includes silver paste and the eutectic structure. The carrying substrates are aluminum oxide (Alumina) and aluminum nitride (AIN) ceramic substrates and metal core PCB (MCPCB). The experimental results show that, under the conditions of the same crystal grain and die attach method, the thermal resistance values for the AIN substrate and the Alumina substrate are 2.1K/W and 5.1K/W, respectively and the total thermal resistance values are 7.3K/W and 10.8K/W. Compared to the Alumina substrate, the AIN substrate can effectively lower the total thermal resistance value by 32.4%. This is because the heat transfer coefficient of the AIN substrate is higher than that of the Alumina substrate, thus effectively increasing its thermal conductivity. In addition, under the conditions of the same crystal grain and the same substrate, the packaging methods are using silver paste and the eutectic structure for die attach. Their thermal resistance values are 5.7K/W and 2.7K/W, respectively, with a variance of 3K/W. Comparisons of the crystal grain structure show that the thermal resistance for the flip chip type is lower than that of the traditional lateral type by 0.9K/W. This is because the light emitting layer of the flip chip crystal grain is closer to the heat-sink substrate, shortening the heat dissipation route, and thus lowering the thermal resistance value. For the total thermal resistance, the crystal grain structure has a lesser effect to the heat dissipation performance whereas the packaging method and the choice of the substrate have a relatively higher effect to the LED heat dissipation performance. Combining the above results, we see that selecting the flip chip crystal grain with a closer light emitting layer to the substrate, the eutectic structure that has better thermal conductivity and the AIN substrate can effectively increase the heat dissipation performance of the LED module.

Effects of Diode Voltage and Thermal Resistance on the Performance of Multichip LED Modules

This paper investigated the thermal characteristics of multichip LED modules under varying chip distances, driving currents, and number of chips in both parallel and series connections. The experimental results showed that, under the same input power, the thermal resistance and junction temperature were higher in series than in parallel due to the different diode resistances of individual chips. The deviations increase with increasing input power. Diode resistance variations significantly affected the current distributions in LED modules due to the restricted constant forward voltage in parallel connections. Nonlinear incremental increases in thermal resistance also enhanced the temperature nonuniformity in the LED module with increasing driving current. The theoretical approach substantially underestimates the junction temperature for two-chip and four-chip modules in both parallel and series connections, especially when the input power is high. The results are helpful for designing high-performance and long-term reliability multichip LED lighting modules.

Новые конструктивно-технологические решения свето¬диодных модулей для ламп-ретрофитов

The authors propose fundamentally new design-technological solutions for compact volumetric mirrorized LED modules with increased power. Test samples of volumetric light-effective LED light effective modules with a power of 10—15 W and light output of 105—160 lm/W for domestic retrofit lamps based on high-efficiency SMD, mini COB, and COB LEDs of third generation were manufactured and tested. Positive technical and practical results were obtained by increasing by over 4—6 times the size of holders — heat sinks (compared to LED modules of flat holders) for heat dissipation from the LEDs by conduction and heat radiation, as well as by increasing light efficiency of LED lamps due to the additional light re-reflection by mirrorized reflectors-radiators in the bulb which is diffuser of the lamp light.

The effect of radiation of LED modules on the growth of dill (Anethum graveolens L.)

AbstractLight quality is thought to affect the growth and development of plants. We examined how light influences the growth and content of some chemical compounds in dill (Anethum graveolens L.). The plants were grown under different light quality. The share of orange and green light in the spectrum was constant and amounted to 10% for either colour. In the first combination (A, 70/10), there was 70% of red light and 10% of blue light. Other combinations had the following proportions: B 60/20, C 50/30, D 40/40 and E 30/50 of red and blue light. The PPFD was about 155 μmol m-2 s-1. Blue light inhibited the elongation growth as well as leaf area. It had positive influence on the accumulation of dry mass, glucose and fructose in the herb. In the combinations with higher percentage of red light the plants were characterised by higher content of essential oils, macronutrients and zinc. To sum up, we can say that the proportion of red and blue light has significant influence on the morphological qualities, chemical composition and dynamics of photosynthesis in these plants. On the other hand, the selection of spectral composition of LEDs will depend on the result we want to achieve.

纳米银焊膏封装大功率COB LED模块的性能研究

In order to improve the thermal performance of the high-power LED,the novel nanosilver paste with higher melting temperature and thermal / electrical conductivity was used as die-attach material,and Al2O3-based ceramic substrates were used to form a high-power LED chip-on-board( COB) architecture. To compare the effect of die attach material,high power COB LED modules were packaged by nanosilver paste,traditional Sn / Ag3. 0 / Cu0. 5 solder and silver epoxy,respectively. The photoelectricity properties of three kinds of LEDs under various ambient temperatures from 27 to 120 ℃ were measured to evaluate their thermal management. The accelerated degradation testing under 100 ℃ was measured to evaluate the reliability. The test results show that the nanosilver paste is a very promising die-attach material for high power multi-chip modules packaging.

방열특성 제어를 위한 PWM 전류제어 기반 LED 모듈 개발

This paper shows significant methods that improve the lifespan of LED modules as well as efficiently using an aluminum heat-sink for LED module in high power. It proposes a method that raises stability and lifespan to protect LED modules and the power unit when the LED module has been used for a long hours at high temperatures. During the research, we applied a method of pulse-width modulation (PWM) in order to prevent the phenomenon that the entire power of a system is turned off and the lifespan is reduced when the LED nodule reacts to the high temperatures. To protect the LED module and SMPS based on high efficiency, a temperature sensor is attached underneath the circuit board and the sensor measures the temperature of circuit board when the LED module is powered on. The electrical power connected to SMPS is controlled by PWM when the temperature of the LED module reaches a particular temperature.

CVD 다이아몬드가 코팅된 알루미늄 방열판의 방열 특성

Nanocrystalline diamond(NCD) coated aluminium plates were prepared and applied as heat sinks for LED modules. NCD films were deposited on 1 mm thick Al plates for times of 2 - 10 h in a microwave plasma chemical vapor deposition reactor. Deposition parameters were the microwave power of 1.2 kW, the working pressure of 90 Torr, the CH4/Ar gas ratio of 2/200 sccm. In order to enhance diamond nucleation, DC bias voltage of �90 V was applied to the substrate during deposition without external heating. NCD film was identified by X-ray diffraction and Raman spectroscopy. The Al plates with about 300 nm thick NCD film were attached to LED modules and thermal analysis was carried out using Thermal Transient Tester (T3ster) in a still air box. Thermal resistance of the module with NCD/Al plate was 3.88 K/W while that with Al plate was 5.55 K/W. The smaller the thermal resistance, the better the heat emission. From structure function analysis, the differences between junction and ambient temperatures were 12.1 o C for NCD/Al plate and 15.5 o C for Al plate. The hot spot size of infrared images was larger on NCD/Al than Al plate for a given period of LED operation. In conclusion, NCD coated Al plate exhibited better thermal spreading performance than conventional Al heat sink.

Design of Circle Array Pattern for Transparent Nanomesh-Type Electrodes.

In this study, we report simulation results for the optical properties of nanomesh-type electrodes for transparent electrode. Usually, indium tin oxide (ITO) is commonly used for transparent conductor to solar cell, display, LED and other electronic modules. However, the cost is high due to the rarity of indium. An alternative way is use of transparent nanomesh-type metal electrode for solar cell. Finite different time domain (FDTD) method was used to simulate and analyze their optical properties. Various array patterns (square, circle and circle hexagonal array) of metal on glass (SiO2) substrates were designed and their properties of transmission and reflection were simulated by using the broad band (λ = 300~1200 nm) plane wave source. To compare basic characteristics of each pattern, various structural parameters such as hole diameter, pitch and metal thickness were applied. The effect of three typical metals, such as Ag, Au, and Al was also compared. In the results, we will discuss about large dip of transmission appeared at the particular wavelength region from the circle array pattern, which is design with pitch of 500 nm at the wavelength range 700 to 800 nm. The surface plasmonpolaritons (SPP) effect can be the cause of large dip and we could find a broad and high transmission from the properly designed in nanomesh-type electrodes, which was calculated as a function of wavelength.

Print Copper on Ceramic for High Reliability Electronics

In the power electronics world, Direct Bonded Copper (DBC) is the primary substrate technology. In this paper, we will discuss an alternative technology utilizing screen printable copper pastes (Thick Printed Copper - TPC) on a variety of substrate technologies including Alumina (Al2O3) and Aluminum Nitride (AlN). These materials when processed, look and perform similar to DBC, but exhibit superior reliability and excellent design flexibility. DBC has drawbacks when it comes to thermal mechanical reliability and lacks the flexibility to have multiple copper thicknesses for power and signal circuits within the same design, which is easily achieved via screen printing. The benefits of this TPC system will be demonstrated through data generated on passive thermal shock tests in comparison to high end DBC. Furthermore, this Thick Print Copper technology has the excellent potential for replacing high end Metal Core Printed Circuit Board (MCPCB) technology due to utilization of higher thermal conductive dielectric materials like Al2O3 and AlN. This will allow for designers to drive their LED's harder and effectively producing LED modules with higher power densities.

태양광을 활용한 스마트 다운재킷 개발 및 보온성능 평가

This study aimed at developing a down jacket prototype that utilized sunlight as an alternative energy source with no air pollution. The jacket is filled with flexible solar panels and has a heat-generating function and LED function. In this study, three smart down jacket prototypes were developed, and the jacket's capabilities were demonstrated through the thermal effect on the performance test. The typical output voltage of the flexible solar panels was 6.4V. By connecting the 2 solar cell modules in series, the final output voltage was 12.8V. A battery charge regulator module was used the KA 7809 (TO-220) of 9V. Three heating pads were to be inserted into the belly of the jacket as direct thermal heating elements, and the LED module was configured, separated by a flash and an indicator. The smart down jacket was designed to prevent damage to the down pack without the individual devices' interfering with the human body's motion. Because this study provides insulation from extreme cold with a purpose, the jacket was tested for heat insulation properties of non-heating, heating on the back, heating on the abdomen, and heating on both the back and abdomen in a sitting posture in a static state. Thermal property analysis results from examining the average skin temperature, core temperature, and the temperature and humidity within clothing showed, that placing a heating element in one place was more effective than distributing the heating elements in different locations. Heating on the back was the most effective for maintaining optimal skin temperature, core temperature, and humidity, whereas heating on the abdomen was not effective for maintaining optimal skin temperature, core temperature, or humidity within clothing because of the gap between the jacket and the body.

Optical design of an LED motorcycle headlamp with compound reflectors and a toric lens

An optical design for a new white LED motorcycle headlamp is presented. The motorcycle headlamp designed in this study comprises a white LED module, an elliptical reflector, a parabolic reflector, and a toric lens. The light emitted from the white LED module is located at the first focal point of the elliptical reflector and focuses on the second focal point. The second focal point of the elliptical reflector and the focal point of the parabolic reflector are confocal. We use nonsequential rays to improve the optical efficiency of the compound reflectors. The toric spherical lens allows the device to meet the Economic Commission of Europe, regulation no. 113 (ECE R113). Furthermore, good uniformity is obtained by using aspherical surface optimization of the same toric lens. The reflectivity of the reflector is 95%, and the transmittance of each lens surface is 98%. The average deviation of the high beam is 14.17%, and the optical efficiency is 66.45%.

COB Line형 LED를 사용한 PAR 조명의 제작

Article history: In this paper, the band structural design that is typically in a line was arranged in a ring shape, so as to configure the high power LED lighting in such a way as to form a concentrated light distribution angle of less than 15 degrees. The parabolic aluminized reflector PAR38 that facilitates design using area and the area of the optical system to the same extent, applied a multiple light-source condenser lens optical system for the control of integration. The LED used here implemented a single linear light source using ans LED module with ans LED, flip-chip chip-scale package. The optical system was designed based on the energy star standard.

Experimenting and Simulating Thermoelectric Cooling of an LED Module

Use of a thermoelectric component (TEC) for an LED module cooling will be studied. The issue will be approached by revealing the operation of a thermoelectric component known also as Peltier element, and the main equations describing its behaviour. An experimental setup including an LED module, a TEC, an heatsink and a fan will be build. Heat dissipation and the electrical performance measurements of the hole experimental setup will be conducted. The benefits and the limitations of TEC used in cooling, will be revealed. Cooling effect versus used electrical power will be studied. 3D thermal simulations for the experimental setup using a FEM simulation software will be presented. Alternatively, a standard circuit simulator will be used. A spice model, which imports TEC's parameters from the data sheet, will be developed. The spice simulation results are compared with the experimental results.

자연대류상의 LED 모듈의 경량열관리를 위한 하이브리드 휜 히트싱크의 수치적으로 조사된 열성능

자연대류상의 LED 모듈의 경량열관리를 위한 하이브리드 휜 히트싱크의 수치적으로 조사된 열성능

Development of LED Module based on Adjustable AC Line Direct SMPS

In this paper, we perform an AC direct input using PA2200Q driver IC module to improve efficiency of LED. In consideration of durability of LED module and its light module and low cost, This LED light module without using any external capacitors and inductors can be adjust a current waveform automatically in order to accomplish a low noise and high power factor including temperature adaptability. There are also the advantages of not only providing wide range of input voltage (200-260VAC) with 50/60Hz but also improves EMI and power factor as well as decreasing harmonics with sequentially current tracking method.