• 한국전기전자재료학회논문지
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• 제28권10호
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• pp.676-681
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• 2015

Recently many studies being carried out to increase the light efficiency of LED. The external quantum efficiency of LED, generally the light efficiency, is determined by the internal quantum efficiency and the light extraction efficiency. The internal quantum efficiency of LED was already reached to more than 90%, but the light extraction efficiency is still insufficient compared with the internal quantum efficiency because the total internal reflection is generated in the interface between the LED chip and air. Thus, we studied about flip chip LED with PSS and performed the optical simulation which find more optimized PSS for flip chip LED to increase the light extraction efficiency. Decreasing of the total internal reflection and effect of diffused reflection according to PSS improved the light extraction efficiency. To get more higher the efficiency, we simulated flip chip with PSS that the parameters are arrangement, edge spacing, radius, height and shape of PSS.

• 문화기술의 융합
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• 제7권1호
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• pp.564-569
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• 2021

본 연구에서는 일반적인 구조의 LED와 경사진 구조의 LED에 대하여, 전극이 없을 때와 전극에서 20%의 흡수(80% 반사)가 발생할 때, 그리고 전극에서 60%의 흡수(40% 반사)가 발생할 때로 구분하여, 전극에서의 흡수와 활성 영역의 높이가 광추출 효율 및 평균 광자 진행 거리에 미치는 영향을 조사하고, 활성 영역의 적절한 높이를 제안하였다. 일반적인 LED에서 전극의 흡수가 증가할수록, 광추출 효율은 18%에서 15%, 13%로 낮아지고, 활성 영역의 높이가 두 전극 사이의 정 중앙에 위치할 때 가장 광 추출 효율이 높다. 경사진 구조의 LED에서는 전극의 흡수가 증가할수록, 광추출 효율은 38%에서 33%, 25%로 낮아지고, 활성 영역의 높이가 두 전극 사이의 정 중앙에 위치할 때 가장 광 추출 효율이 높다. 경사진 구조의 LED는 일반적인 LED 보다 광추출 효율을 두 배 이상 높일 수 있다. 이는 전반사에 의해 광자가 칩 내부에 갇히는 현상을 줄여주기 때문이다.

• Journal of Power Electronics
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• 제16권2호
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• pp.815-822
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• 2016

The efficiency of light-emitting diode (LED) devices is a significant factor that reflects the capability of these devices to convert electrical power into optical power. In this study, a method for estimating the efficiency of LED devices is proposed. An efficiency model and a heat power model are established as convenient tools for LED performance evaluation. Such models can aid in the design of LED drivers and in the reliability evaluation of LED devices. The proposed estimation method for the efficiency and heat power of LED devices is verified by experimentally testing two types of commercial LED devices.

• Journal of the Optical Society of Korea
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• 제17권1호
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• pp.22-26
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• 2013

The author analyzes the luminous efficiency of the phosphor-conversion white light-emitting diode (LED) that consists of a blue LED chip and a yellow phosphor. A theoretical model is derived to find the relation between luminous efficiency (LE) of a white LED, wall-plug efficiency (WPE) of a blue LED chip, and the phosphor absorption ratio of blue light. The presented model enables to obtain the theoretical limit of LE and the lower bound of WPE. When the efficiency model is applied to the measured results of a phosphor-conversion white LED, the limit theoretical value of LE is obtained to be 261 lm/W. In addition, for LE of 88 lm/W at 350 mA, the lower bound of WPE in the blue LED chip is found to be ~34%. The phosphor absorption ratio of blue light was found to have an important role in optimizing the luminous efficiency and colorimetric properties of phosphor-conversion white LEDs.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 추계학술발표강연 및 논문개요집
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• pp.21-21
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• 2003

To increase the light-emission efficiency of LED, we increased the internal and external quantum efficiency by suppressing the defect formation in the quantum well and by increasing the light extraction efficiency in LED, respectively. First, the internal quantum efficiency was improved by investigating the effect of a low temperature (LT) grown p-GaN layer on the In$\sub$0.25/GaN/GaN MQW in green LED. The properties of p-GaN was optimized at a low growth temperature of 900oC. A green LED using the optimized LT p-type GaN clearly showed the elimination of blue-shift which is originated by the MQW damage due to the high temperature growth process. This result was attributed to the suppression of indium inter-diffusion in MQW layer as evidenced by XRD and HR-TEM analysis. Secondly, we improved the light-extraction efficiency of LED. In spite of high internal quantum efficiency of GaN-based LED, the external quantum efficiency is still low due to the total internal reflection of the light at the semiconductor-air interface. To improve the probability of escaping the photons outside from the LED structure, we fabricated nano-sized cavities on a p-GaN surface utilizing Pt self-assembled metal clusters as an etch mask. Electroluminescence measurement showed that the relative optical output power was increased up to 80% compared to that of LED without nano-sized cavities. I-V measurement also showed that the electrical performance was improved. The enhanced LED performance was attributed to the enhancement of light escaping probability and the decrease of resistance due to the increase in contact area.

• 한국인터넷방송통신학회논문지
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• 제16권3호
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• pp.109-113
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• 2016

본 논문에서는 LED 조명 모듈의 소비전력 절감, 램프의 수명 및 열효율 과 점등 제어 효율성을 높인 다윗 스타 마방진 이용한 효율적인 LED 제어 알고리즘을 제안하다. 기존의 마방진 알고리즘 이용한 점등 방식은 LED의 점등 시간이 줄어들고 교차 점등되기 때문에 그만큼의 발열이 줄어들어 LED의 효율을 높일 수 있었으나 점등 제어를 하는데 한계를 가지고 있다. 제안하는 알고리즘을 적용할 경우에는 LED 조명 모듈의 소비전력 절감과 수명 및 열효율 높이는 동시에 LED의 점등 제어의 효율성을 높일 수 있다. 본 논문이 제안하는 알고리즘은 LED Matrix에 변형 마방진을 이용하여 12개의 구역으로 나누어 완전대칭 되는 패턴을 일정시간 간격으로 이동, 회전 및 반전 기법을 교차 수행하여 패턴을 점등을 하게 된다. 본 논문이 제안하는 알고리즘을 수행하여 기존의 마방진을 이용한 점등 방식과 비교한 결과, 조명의 광속과 소비전력 그리고 발열량의 효율성은 기존 마방진을 이용한 LED 점등방식과 동일하고 제어의 효율성을 높일 수 있었다.

• Journal of the Optical Society of Korea
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• 제19권3호
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• pp.311-316
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• 2015

We investigate the temperature dependence of the phosphor conversion efficiency (PCE) of the phosphor material used in a white light-emitting diode (LED) consisting of a blue LED chip and yellow phosphor. The temperature dependence of the wall-plug efficiency (WPE) of the blue LED chip and the PCE of phosphor are separately determined by analyzing the measured spectrum of the white LED sample. As the ambient temperature increases from 20 to $80^{\circ}C$, WPE and PCE decrease by about 4.5% and 6%, respectively, which means that the contribution of the phosphor to the thermal characteristics of white LEDs can be more important than that of the blue LED chip. When PCE is decomposed into the Stokes-shift efficiency and the phosphor quantum efficiency (QE), it is found that the Stokes-shift efficiency is only weakly dependent on temperature, while the QE decreases rapidly with temperature. From 20 to $80^{\circ}C$ the phosphor QE decreases by about 7% while the Stokes-shift efficiency changes by less than 1%.

• Journal of Biosystems Engineering
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• 제38권4호
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• pp.279-286
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• 2013

Purpose: This study was conducted to analyze the utilization efficiencies of electric energy and photosynthetically active radiation of lettuce grown under red LED, blue LED and fluorescent lamps with different photoperiods. Methods: Red LED with peak wavelength of 660 nm and blue LED with peak wavelength of 450 nm were used to analyze the effect of three levels of photoperiod (12/12 h, 16/8 h, 20/4 h) of LED illumination on light utilization efficiency of lettuce grown hydroponically in a closed plant production system (CPPS). Cool-white fluorescent lamps (FL) were used as the control. Photosynthetic photon flux, air temperature and relative humidity in CPPS were maintained at 230 ${\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, $22/18^{\circ}C$ (light/darkness), and 70%, respectively. Electric conductivity and pH were controlled at 1.5-1.8 $dS{\cdot}m^{-1}$ and 5.5-6.0, respectively. The light utilization efficiency based on the chemical energy converted by photosynthesis, the accumulated electric energy consumed by artificial lighting sources, and the accumulated photosynthetically active radiation illuminated from artificial lighting sources were calculated. Results: As compared to the control, we found that the accumulated electric energy consumption decreased by 75.6% for red LED and by 70.7% for blue LED. The accumulated photosynthetically active radiation illuminated from red LED and blue LED decreased by 43.8% and 33.5%, respectively, compared with the control. The electric energy utilization efficiency (EEUE) of lettuce at growth stage 2 was 1.29-2.06% for red LED, 0.76-1.53% for blue LED, and 0.25-0.41% for FL. The photosynthetically active radiation utilization efficiency (PARUE) of lettuce was 6.25-9.95% for red LED, 3.75-7.49% for blue LED, and 2.77-4.62% for FL. EEUE and PARUE significantly increased with the increasing light period. Conclusions: From these results, illumination time of 16-20 h in a day was proposed to improve the light utilization efficiency of lettuce grown in a plant factory.

• 대한전자공학회논문지SD
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• 제44권4호
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• pp.91-96
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• 2007

사파이어 기반의 GaN LED의 광추출 효율을 시뮬레이션을 이용하여 정량적으로 평가하였다. 각각의 LED는 ray-tracing 시뮬레이션을 이용하여 광추출 효율을 계산하였다. 본 연구에는 PSS(patterned sapphire substrate) LED와 flat LED의 비교 분석을 통하여, LED에서의 사파이어 기판의 패턴이 광추출에 미치는 영향을 설명하였다. 또한, 각각의 칩에서 반사막의 반사도가 광추출에 미치는 영향을 분석하고, 그 원인을 시뮬레이션을 이용하여 설명하였다. 한편, 사파이어 패턴에 의한 광추출효율의 변화 효과를 공기(air)와 실리콘(silicone) 분위기에서 시뮬레이션을 수행하였다. 이러한 시뮬레이션 기술을 통해 광추출 효율의 개선 정도를 정량적으로 평가할 수 있었으며, 이러한 연구가 향후 고효율 LED 개발에 도움을 줄 것으로 판단된다.

• 조명전기설비학회논문지
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• 제27권9호
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• pp.15-22
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• 2013

A new LED lamp driving technology with a charge pump instead of a conventional DC-DC converter is proposed. The proposed driving technology is used to control the LED lamp with digital dimming. The power loss in the zener diodes is reduced because the charging process of the capacitors is selectively controlled according to the digital control signal. From the experimental results, when dimming four LED lamps simultaneously, the average driving circuit efficiency of 89% is obtained, regardless of the dimming level. White light with color temperature over a range of 2800~7200K was produced by dimming control of red, green, blue and amber LED lamps with the proposed driving circuit. The characteristics of the driving circuits can be changed depending on the characteristics of the R, G, B, and A LED lamps. The efficiency of the driving circuits up to a maximum 89% can also be obtained depending on the combination of LED lamps. The driving technology with digital dimming control for LED lamps proposed in this paper would be effective for obtaining high efficiency in LED driving circuits and remote control of LED lamps using digital communications.