• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.2
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• pp.666-671
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• 2016

This paper introduces a device providing close local lighting to the affected part, where the operation-purpose astral lamp alone cannot shed light directly, in an operation room of hospitals or clinics, which helps clinical doctors perform safe treatment of the affected part deep inside a human body. This medical assisting lighting is a device necessary to prevent fatal operation failures, which can occur with minute operation processes, such as tumor removal or angiorrhaphy. The components, such as the light source and power supply were designed to be low power consuming and small in size, have a narrow angle lens was used to increase the light spreading effect and focused illumination. The end-caps of the light transmission device using an optical cable and the lighting device were designed in the waterproof type to enable disinfection of these devices after use for the next patients. According to the measurement of the light source properties made after development of the retractor lighting device, the illumination intensity was 490 lux, the brightness was $11,550cd/m^2$, general color rendering index was 78, color temperature was 11,000K, and the intensity distribution was even, which were confirmed to be adequate for medical assisting local lighting.

• Journal of the Semiconductor & Display Technology
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• v.18 no.1
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• pp.10-14
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• 2019

In this study, we synthesized two $Y_3Al_5O_{12}:Ce^{3+}$ phosphors ($7{\mu}m$-sized and $2{\mu}m$-sized YAG) with different sizes by controlling particles sizes of starting materials of the phosphors for white LED. In the smaller one ($2{\mu}m$-sized YAG), its photoluminescence intensity in the reflective mode was 63 % that of the bigger one ($7{\mu}m$-sized YAG); the quantum efficiencies were 93 % and 70 % for the smaller and the bigger ones. Two kinds of white LED packages with the same color coordinates were fabricated with a blue package (chip size $53{\times}30$) and two phosphors. The luminous flux of the white LED package with the smaller YAG phosphor was 92 % of that with the bigger one, indicating that the quantum efficiency of phosphor dispersed inside LED package was higher than that of the pure powder. It was consistently confirmed by the optical simulation (LightTools 6.3). It is notable according to the optical simulation that the white LED with the smaller phosphor showed 24 % higher luminous efficiency. If the smaller one had the same quantum efficiency as the bigger one (~93 %). Therefore, it can be suggested that the higher luminous efficiency of white LED can be possible by reducing the particle size of the phosphor along with maintaining its similar quantum efficiency.

• Journal of the Korean Ceramic Society
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• v.54 no.6
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• pp.449-469
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• 2017

The development of quantum dots (QDs) has had a significant impact on various applications, such as solar cells, field-effect transistors, and light-emitting diodes (LEDs). Through successful engineering of the core/shell heterostructure of QDs, their photoluminescence (PL) quantum yield (QY) and stability have been dramatically enhanced. Such high-quality QDs have been regarded as key fluorescent materials in realizing next-generation display devices. Particularly, electrically driven (or electroluminescent, EL) QD light-emitting diodes (QLED) have been highlighted as an alternative to organic light-emitting diodes (OLED), mostly owing to their unbeatably high color purity. Structural optimizations in QD material as well as QLED architecture have led to substantial improvements of device performance, especially during the past decade. In this review article, we discuss QDs with various semiconductor compositions and describe the mechanisms behind the operation of QDs and QLEDs and the primary strategies for improving their PL and EL performances.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.2
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• pp.443-449
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• 2015

In this paper, we proposed Channel allocation scheme according to the user's location with IR. In VLC System, LED can generate various colors of light by controlling the mixing ratio of each individual RGB color element. Thus, each RGB channel will have a different signal power, and each channel will have different performance. This proposed system using Visible light(RGB) as way to transmit signals, it depends on the mixture RGB, which decided the color of light, moreover, each things determined their performance. However, if the signal were fixed allocated RGB to transmit such as the original system, the importance of the each signals a different occur the limit on the quality of signals. To solve this problem in this paper, according to the RGB mixture ratios analyze the performance for the LED, which analyzed based on allocating the signal by transmitting to improve the quality was about how researched. In addition, our proposed system is able to improve the performance of BER and satisfied the Qos to desire users.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.30 no.3
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• pp.30-38
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• 2016

In this research, a 6W white LED package with a Glass Remote Phosphor was developed to improve the life of an LED package. The Glass Remote Phosphor was fabricated by the Phosphor in Glass (PiG) method, wherein phosphor YAG:Ce was mixed with glass frit and then heat treated. A paste with 75wt.% of a phosphor substance and 25wt.% glass frit was coated on a glass substrate two times using the screen-printing technique and heat-treated at $800^{\circ}C$ ; this structure gave a luminous efficacy of 136.1lm/W, color rendering index of 74Ra, and color temperature of 5,342K, thus satisfying the requirements as a light source for lighting. Moreover, an IES LM-80 accelerated life test was conducted on the same LED package for 6,000h in order to estimate the L70 lifetime based on IES TM-21. The results showed guaranteed lifetimes of 213,000h at $55^{\circ}C$, 245,000h at $85^{\circ}C$, and 209,000h at $95^{\circ}C$.

• Journal of Bio-Environment Control
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• v.17 no.2
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• pp.116-123
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• 2008

This study was carried out to investigate into the effect of light-emitting diode (LED) for the light quality as a light source on the broccoli seed germination and the physiological activity of vegetable sprouts. We have also germinated seeds of the broccoli and applied LED as a light quality such as blue, green, red, white, yellow and red + blue color lights to their sprouts for 14 hours and kept dark for 10 hours at the temperature of $25^{\circ}C$ (day)/$18^{\circ}C$ (night). Broccoli sprouts were extracted by methanol and their physiological activities were examined. All broccoli seeds were germinated at 3 days after seeding regardless of the light color. Total sprout fresh weight were mostly became highest by 0.389g (10 plants) at 8 days after seeding when their sprouts were grown under blue color light. Total phenol compound contents in broccoli sprouts were extremely increased by $83.0\;mg{\cdot}L^{-1}$ under the white light, and total flavonoid contents were most much more by $72.6\;mg{\cdot}L^{-1}$ under the blue light. DPPH radical scavenging activity at $2,000\;mg{\cdot}L^{-1}$ were most highest by 93.5% in broccoli sprouts grown under the white light. Nitrite radical scavenging activity at the concentration of $500\;mg{\cdot}L^{-1}$ in sprout extracts were the most increased by 66.9% under the yellow light, and tyrosinase inhibition activity at $2,000\;mg{\cdot}L^{-1}$ in sprout extracts were by 14.5% under red light.

• 한국정보디스플레이학회:학술대회논문집
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• 2008.10a
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• pp.557-560
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• 2008

The main goal of this work is to fabricate light emitting diode (LED) module and apply it to mobile handset. We first fabricated the blue-color LED based on the AlInGaN cell structure with size of $200\;{\mu}m\;{\times}\;200\;{\mu}m$. Also we proposed a new $1.0\;mm\;{\times}\;0.5\;mm$ (1005size) packaging procedure for the LED cell. Thus the overall dimension of our LED cell was as small as $1.0\;mm\;{\times}\;0.5\;mm\;{\times}\;0.4\;mm$ ($W\;{\times}\;L\;{\times}\;T$). As far as we knew it was the first time that this small LED cell dimension had been fabricated and operated.

• Journal of rehabilitation welfare engineering & assistive technology
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• v.10 no.2
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• pp.163-170
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• 2016

The purpose of this study was to verify the emotional response of user to LED light colors in healing bed system in cypress tree. Eight colors of LED light were provided including red, orange, yellow, green, blue, indigo, violet and white. And three illumination color temperature were provided including 3,000K, 5,000K, 8,000K. Seven subjects in their twenties were involved without the medical history of eyes and heart disorders. The subjects were exposed to LED lighting during 5 minutes and their emotional response was evaluated through the following: first, at the physiological effect heart rate variability(HRV) was measured during the stimulation; second, at the emotion level the subjects were asked about lighting color and color temperature through a survey. Results, lower color temperature of 3,000K and green color shows high value on HRV. We have found that there is a difference of physiological and emotion level effect depending on color stimulus. This study could be applied to reference data to analysis of a decrease in fatique and charges of brain waves for color stimulus.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.60 no.4
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• pp.253-256
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• 2011

LEDs have small size, long lifespan, high reliability, low power consumption and high color efficiency. Using such a characteristics, LED Back Light Unit has been studying actively. This paper proposes LED driver to minimize power consumption due to LED forward voltage($V_F$) difference and temperature rising. Compared to conventional LED driver, the proposed driver have excellent stability, brief structure and linear output voltage of DC-DC boost converter. Proposed LED Driver circuit was designed using 0.35um CMOS technology. And its operation was verified through simulation.

• Transactions on Electrical and Electronic Materials
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• v.3 no.4
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• pp.21-26
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• 2002

Color correction methods of chromaticity coordinates using Color Matching Function (CMF) were studied to develop a device-independent portable-type urine analyzer. The reflection spectra were measured for the degrees of 10 test items of the urine reagent strip (urine strip) to develop a portable-type urine analyzer. A computer simulation was performed to quantitatively distinguish the color reactions of the urine system, by using the spectral power distribution of Light Emitting Diode(LED), the reflection of a urine strip, and spectral sensitivity of a photodiode. To develop a device-independent system, chromaticity coordinates were modified to reduce the color deviations in the urine strip, by using the temperature compensation of LED and the color transformation by CMF. The experimental values obtained by developed urine system exhibited the accuracy above 95% for all color samples.