• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1343-1348
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• 2008

LEDs which have many merits are widely used in the field of light devices, and have rapidly replaced old light devices such as incandescent or fluorescent lamps. Long life, on the order of 50,000 to 100,000 hours, is one of the key features of light emitting diodes(LEDs) that has attracted the lighting community to this technology. High Power white LEDs have yet to demonstrate this capability. This paper planed accelerated life test that has two factor(temperature, current) and two levels. Finally, using ALTA programs, we estimated the common shape parameter of Weibull distribution, life-stress relationship, B10 life and accelerating factors.

• Transactions on Electrical and Electronic Materials
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• v.8 no.2
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• pp.93-96
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• 2007

LCD (liquid crystal display) industry is needed to goods of high reliability and is interested in products without harmful material. In this experiment, we made the LED backlight unit for Automotive-navigation. And for making this backlight unit we used to eight side emitting type white LEDs with 1 W high power of the lumileds company. We could know that this backlight unit releases to 6500 nit in 14 W power consumption and start up voltage time is under the 15ms in the ambient temperature $-20\;^{\circ}C$.

• Journal of Sensor Science and Technology
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• v.30 no.2
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• pp.99-104
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• 2021

In this study, we utilized the duty factor of the transition frequency modulation (TFM) for the illumination control of the light emitting diode (LED) light in visible light communication (VLC). The average optical power is linearly proportional to the duty factor in TFM waveforms. We used the transition frequencies of Na=5 and Nb=1 for the high and the low bits, respectively, of the non-return-to-zero (NRZ) data in the VLC transmitter. A resistor and capacitor high-pass filter (HPF) was used in the VLC receiver to eliminate the 120 Hz optical noise from adjacent lighting lamps and the spikes at the HPF output were used to recover NRZ data from the TFM waveform. In experiments, the illumination of the LED light was controlled in the range of 25-90% of the constant-wave optical power by changing the duty factor of the TFM waveforms.

• The Journal of the Korea institute of electronic communication sciences
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• v.13 no.1
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• pp.85-92
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• 2018

In this paper, we designed a 150W LED lighting SMPS circuit operating at $-40^{\circ}C$. We designed a 150W LED lighting constant current circuit for the characteristics of the SMPS and fabricated and measured. The operating temperature range for a 150W LED lighting SMPS circuit is -40 to $70^{\circ}C$ and SMPS predicted life was 1.29-2.25 years based on 24 hours. The high acceleration life test and EMI test confirmed no abnormality.

• Journal of the Korean Solar Energy Society
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• v.31 no.2
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• pp.113-119
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• 2011

LED lighting has received much attention in recent years due to its high energy efficiency and environmental friendliness. As the color of light can be obtained by adjusting the light intensity of LEDs, the quality of visual environment can be improved. The aims of this study are to develop a wavelength adjustable LED lighting system and to examine its lighting performances. The LED lighting system and experimental cell for assessment of the lighting performance were constructed. This LED lighting system is able to materialize the various spectral power distribution and color temperature of light through the control of the four dimmers. Up to $432^4$ kinds of light combinations are possible. The range of illuminance on workplane were measured as 7~1,831 ㏓. Improvement of psychological and physical functions for occupants can be expected according to control of lighting performances.

• Korean Journal of Human Ecology
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• v.19 no.6
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• pp.1053-1062
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• 2010

To assist the further development of hight-visibility clothing this study compared the visibility and subjective wear sensation of commercial protective vests with retro-reflecting materials or LEDs. Nine subjects compared high-visibility vests to evaluate how easy they were to see when exposed to the headlight of a car at night, and the subjects assessed the wear sensation of the vests also. The intensity and visibility of five different colored LEDs assembled on the five substrates separately were also evaluated to select the suitable LED color for night protective clothing. The intensity of illumination was measured by an illuminometer, and the visibility was evaluated by 11 participants both in a dark room and in front of a car outdoors at night. Results showed, the most effective LEDs were high intensity LEDs which shift blinking red and white were most effective. However, excessively high intensity of illumination could decrease the working efficiency. In subjective wear evaluation, the most favorable vest had a front opening, were adjustable at the sides, and had an electric power switch on the front of the vest.

• Proceedings of the Materials Research Society of Korea Conference
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• 2003.11a
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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.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.2
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• pp.111-118
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• 2010

Recently, LCD TV using LED backlight has a great attention due to its low power consumption, slim construction, mercury free, wide color gamut and fast response. For the uniform brightness of the LCD panel, multi channel LEDs and DC/DC converter for each LED are required in conventional system. Therefore energy conversion efficiency is poor, the system size bulky and the cost of production high. To overcome these above mentioned drawbacks, a new current-balancing multi-channel LED driver is proposed in this paper. It can not only drive multi-channel LEDs with one DC/DC converter but also provide all LEDs with constant balanced current. To confirm the validity of the proposed driver, its operation and performance are verified on a prototype for 46" LCD TV.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.25 no.12
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• pp.34-41
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• 2011

In order to understand the thermal performance of each LED chips in multi-chip LED package, a quantitative parametric analysis of the temperature evolution was investigated by thermal transient analysis. TSP (Temperature Sensitive Parameter) value was measured and the junction temperature was predicted. Thermal resistance between the p-n junction and the ambient was obtained from the structure function with the junction temperature evolution during the cooling period of LED. The results showed that, the thermal resistance of the each LED chips in 4 chip-LED package was higher than that of single chip- LED package.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2006.05a
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• pp.443-444
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• 2006

The influence of the heat sources on LED junction temperature are Engine room air, Back plate, Electric power device, and so on. LED lamp cooling system is considered to be an important subject fur high light efficiency. Because LED Chip will be problem When LED junction temperature be over $135^{\circ}C$, In this Study, The Looped Heat Pipe System is considered to prevent LED Chip fall. The LHPS is consist of evaporator part, condenser part, heat pipe part. The working fluid of LHPS is HCFC-123. In this study, to prevent LED Chipfall, we study thermal characteristics for Looped Heat Pipe System with LED lamp.