• Bulletin of the Korean Chemical Society
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• v.33 no.8
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• pp.2523-2528
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• 2012

Green phosphors $(Zn_{1-a-b}M_aM^{\prime}_b)_xGa_yS_{x+3y/2}:Eu^{2+}$ (M, M' = alkali earth ions) with x = 2 and y = 2-5 were prepared, starting from ZnO, MgO, $SrCO_3$, $Ga_2O_3$, $Eu_2O_3$, and S with a flux $NH_4F$ using a conventional solidstate reaction. A phosphor with the composition of $(Zn_{0.6}Sr_{0.3}Mg_{0.1})_2Ga_2S_5:Eu^{2+}$ produced the strongest luminescence at a 460-nm excitation. The observed XRD patterns indicated that the optimized phosphor consisted of two components: zinc thiogallate and zinc sulfide. The characteristic green luminescence of the $ZnS:Eu^{2+}$ component on excitation at 460 nm was attributed to the donor-acceptor ($D_{ZnGa_2S_4}-A_{ZnS}$) recombination in the hybrid boundary. The optimized green phosphor converted 17.9% of the absorbed blue light into luminescence. For the fabrication of light-emitting diode (LED), the optimized phosphor was coated with MgO using magnesium nitrate to overcome their weakness against moisture. The MgO-coated green phosphor was fabricated with a blue GaN LED, and the chromaticity index of the phosphor-cast LED (pc-LED) was investigated as a function of the wt % of the optimized phosphor. White LEDs were fabricated by pasting the optimized green (G) and the red (R) phosphors, and the commercial yellow (Y) phosphor on the blue chips. The three-band pc-WLED resulted in improved color rendering index (CRI) and corrected color temperature (CCT), compared with those of the two-band pc-WLED.

• Design & Manufacturing
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• v.7 no.1
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• pp.55-59
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• 2013

A Light Emitting Diode(LED) is a semiconductor device which converts electricity into light. LEDs are widely used in a field of illumination, LCD(Liquid Crystal Display) backlight, mobile signals because they have several merits, such as low power consumption, long lifetime, high brightness, fast response, environment friendly. In general, LEDs production does die bonding and wire bonding on board, and do silicon and phosphor dispensing to protect LED chip and improve brightness. Then lens molding process is performed using mixed liquid silicon rubber(LSR) by resin and hardener. A mixture of resin and hardener affect the optical characteristics of the LED lens. In this paper, computational design of static mixer was performed for mixing of liquid silicon. To evaluate characteristic of mixing efficiency, finite element model of static mixer was generated, and fluidic analysis was performed according to length of mixing element. Finally, optimal condition of length of mixing element was applied to static mixer from result of fluidic analysis.

• Journal of Plant Biotechnology
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• v.41 no.2
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• pp.94-99
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• 2014

This study was conducted to elucidate the effect of light sources and explant types on in vitro shoot multiplication and rooting of a rare and endangered plant Abeliophyllum distichum. Both apical buds and axillary buds were used as explants under 4 different light sources, cool white florescent light (F), 100% blue light-emitting diode (LED) (B), 50% blue and 50% red LED mixture (BR), and 100% red LED (R). Clear difference was observed in terms of shoot proliferation by light sources types but not by position-dependent explant types. Multiple shoot induction rates were enhanced under both B and BR light sources. Spontaneous rooting was induced in shoot induction medium under B light source. Both the rates of rooting and numbers of roots per explant were higher in apical bud explants compared to axillary bud explants. Interestingly R light source stimulated shoot elongation but inhibited root development. Therefore, our results suggest that the use of apical bud explants under B or BR light sources is suitable for in vitro micropropagation of a rare and endangered plant species, Abeliophyllum distichum.

• Fashion & Textile Research Journal
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• v.15 no.5
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• pp.834-840
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• 2013

This study aims to suggest practical considerations for designing protective clothing with increased visibility that will have higher user acceptance by law enforcement officers. Light-emitting diode(LED) patrol vests were visually and structurally assessed, and 125 police officers' responses from surveys about user acceptance of the vest were analyzed. The current LED patrol vest was designed for enhanced safety of police officers by increasing visibility in the dark. However, the user acceptance rate of the LED patrol vest indicates low use of and low satisfaction with the vest despite its enhanced safety features. In particular, differences in materials, design, functionality of the pockets and size of the vest depending on the hours worked, were statistically significant. The police officers' responses suggest areas of improvement in design, materials, ease of movement, size and functionality. Key issues include 'tactile discomfort'; 'impeded vision from the glare of the LED'; 'frequent malfunctions of the LED'; 'impossible repair of the broken LED units'; 'no user feedback'; 'inconvenient to replace batteries'; 'brittle materials' and 'unpleasing look'. To increase user acceptance, designer should incorporate context-awareness, a convenient user interface, a modular design approach, first responders' self-image as public servants in relation to their aesthetic perspectives of their uniforms, and scientific evaluation of the effectiveness of the intended functions of the clothing. Suggested implications for designing the LED patrol vest can be applied to designing other functional/protective clothing for intended end users with special needs.

• Journal of the Korea Society of Computer and Information
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• v.19 no.2
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• pp.109-115
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• 2014

The research on solar energy that we get from nature to cope with energy exhaustion is a very significant and inevitable task for us to do. Along with this, lately, in Korea, as part of new growth engine industry regarding low-carbon green growth, we have selected the LED(Light Emitting Diode) as low power consuming, eco-friendly lighting equipment and have been facilitating research and development on it and creating a variety of new industries utilizing it. What was developed here in this research was the photovoltaic LED lighting system applying lithium polymer batteries equipped with the excellent performance of lithium ion batteries as well as significantly low explosive hazard. Its photovoltaic panel was made to have 100W capacity, and for its power supply system, functional convenience was considered so that it could be equipped with both DC and AC power to be used as household electricity in a variety of ways.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.5
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• pp.1-7
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• 2010

LEDs, compared to conventional light sources, have many advantages and their applications are rapidly expanding, especially in areas such as back-lights for LCD. In this paper, we propose a new LED lamp structure suitable for applications requiring a low power. In the proposed LED lamp structures, LED chips are mounted on a transparent polycarbonate plate, and thus photons are transmitted through the both sides of the plate. The copper layer deposited on the polycarbonate plate is patterned to form circuit patten and the chip mount pad, on which LED chips are mounted. We speculate that our proposed LED lamp structures may be used as a type of plate light source.

• JSTS:Journal of Semiconductor Technology and Science
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• v.6 no.3
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• pp.199-205
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• 2006

Patterned sapphire substrates (PSS) were fabricated by a simple wet etching process with $SiO_2$ stripe masks and a mixed solution of $H_2SO_4$ and $H_3PO_4$. GaN layers were epitaxially grown on the PSS under the optimized 2-step growth condition of metalorganic vapor deposition. During the 1st growth step, GaN layers with triangular cross sections were grown on the selected area of the surface of the PSS, and in the 2nd growth step, the GaN layers were laterally grown and coalesced with neighboring GaN layers. The density of threading dislocations on the surface of the coalesced GaN layer was $2{\sim}4\;{\times}\;10^7\;cm^{-2}$ over the entire region. The epitaxial structure of near-UV light emitting diode (LED) was grown over the GaN layers on the PSS. The internal quantum efficiency and the extraction efficiency of the LED structure grown on the PSS were remarkably increased when compared to the conventional LED structure grown on the flat sapphire substrate. The reduction in TD density and the decrease in the number of times of total internal reflections of the light flux are mainly attributed due to high level of scattering on the PSS.

• Journal of Conservation Science
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• v.36 no.4
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• pp.236-243
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• 2020

In this study, an accelerated aging experiment for fabric and paper was conducted using two light emitting diode(LED) sources with different wavelength characteristics, and the discoloration under each lighting type was examined. Hanji(Korean traditional paper) and related textiles showed more discoloration under blue LEDs, while the blue wool standard showed more discoloration under white LEDs. This, indicated that the deterioration varied depending on the sample color. The the effect of the light source on artifact deterioration was primarily related to the total radiation flux(expressed in mill watts), rather than the total luminous flux(expressed in lumens). In addition, the discoloration of the investigated artifacts was dependent on the color rendering of the lighting.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.736-739
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• 2002

We report on white light emission from a light emitting diode(LED) prepared by blending a red emitting copolymer, m-SiPh PPV-co-MEH PPV, and a blue emitting polyvinylcarbazole (PVK). White light emission was realized when the weight ratio of the m-SiPh PPV-co-MEH PPV : PVK equals to 1 : 30, in which the commission Internationale de L'Eclairage coordinates were x=0.3266 and y=0.3438.

• Current Optics and Photonics
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• v.2 no.5
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• pp.468-473
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• 2018

We investigate the temperature dependence of efficiency droop in InGaN/GaN multiple-quantum-well (MQW) blue light-emitting diodes (LEDs) in the temperature range from 20 to $80^{\circ}C$. When the external quantum efficiency (EQE) and the wall-plug efficiency (WPE) of the LED sample were measured as injection current and temperature varied, the droop of EQE and WPE was found to be reduced with increasing temperature. As the temperature increased from 20 to $80^{\circ}C$, the droop ratio of EQE was decreased from 16% to 14%. This reduction in efficiency droop with temperature can be interpreted by a temperature-dependent carrier distribution in the MQWs. When the carrier distribution and radiative recombination rate in MQWs were simulated and compared for different temperatures, the carrier distribution was found to become increasingly homogeneous as the temperature increased, which is believed to partly contribute to the reduction in efficiency droop with increasing temperature.