• Journal of Bio-Environment Control
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• v.28 no.3
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• pp.265-272
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• 2019

The purpose of this study was to investigate the effects of LED and QD-LED (Quantum Dot) irradiation on seed germination, antioxidant ability, and microbial growth, during red radish (Raphanus sativus L.) sprouts cultivation. Irradiated light was blue, red, blue + red and blue + red + far red (QD-LED) lights, and the controls were a fluorescent lamp (FL), and dark condition. Germination rate of red radish was highest in the dark condition. The plant height and fresh weight of red radish sprouts that irradiated each light for 24 hrs after 7 days growing in dark condition, did not shown significantly difference among treatments. After 24 hrs of light irradiation, cotyledon green was best in blue + red light, and the red hypocotyl was excellent in blue light and QD-LED light. DPPH and phenol contents were high in dark and blue + red light treatment, and anthocyanin content was high in blue light and QD-LED light. Total aerobic counts were similar in all treatments and did not show bactericidal effect, whereas E. coli count was lowest in QD-LED light treatment, and yeast and mold counts were lowest in FL only treatment. Results suggest that when red radish seeds were germinated in dark condition and cultivated for 7 days as sprouts, and then treated with blue light or QD-LED light for 24 hrs, the seeds produced good quality red radish sprouts with greenish cotyledon, reddish hypocotyl, high anthocyanin content, and lower level of E coli contamination.

• Journal of the Korean Society of Marine Environment & Safety
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• v.21 no.1
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• pp.1-8
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• 2015

We investigated the effect of monochromatic light emitting diode (LED) on the growth of diatoms Nitzschia sp., Phaeodactylum tricornutum, Skeletonema sp. and green algae Chlorella vulgaris. The four microalgae species were cultured under blue LED (450 nm), yellow LED (590 nm), red LED (650 nm) and fluorescent lamp (mixed wavelengths). The maximum growth rates and cell densities of Nitzschia sp., P. tricornutum and Skeletonema sp. were highest under blue LED, followed by fluorescent lamp, red LED and then yellow LED, however those of C. vulgaris were highest under red LED. This result indicates that blue LED is favorable for the growth of diatoms. Thus, the growth of microalgae under monochromatic light might be species-specific or taxon-specific. Also, these results could be used as an important information in future for remediation of heavy metal contamination in the sediments using LED and microalgae.

• Proceedings of the Optical Society of Korea Conference
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• 2001.02a
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• pp.48-49
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• 2001

GaN는 wurzite structure를 갖는 wide bandgap III-V족 반도체로서, 청색 반도체 laser diode (LD), light emitting diode (LED)등으로 응용되는 물질이다. InGaN quantum well은 GaN계의 청색 LD, LED 구조에서 활성층으로 사용되기 때문에 이에 대한 광학적 연구가 활발하다. InGaN는 GaN위에 성장하면 strain에 의해 piezoelectric 효과가 크게 나타나는 것으로 알려져 있다. 이러한 piezoelectric potential에 의해 외부에서 voltage가 가해지지 않은 상황에서도 InGaN quantum well내의 electron, hole의 wave function이 비대칭 potential의 영향을 받게된다. (중략)

• Journal of Applied Biological Chemistry
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• v.62 no.2
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• pp.181-186
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• 2019

The optimum design of LED device for irradiation of 460 nm blue light on extruded rice cake using simulation and the effect of the blue light on the inactivation of Bacillus cereus (B. cereus) group on the rice cake were investigated. The irradiated light intensity patterns on the surface area of the sample were simulated with three different LED arrays (centered, cross, and evenly spaced) and at various distances (22, 32, 42 mm) between the LED modules and the sample. In addition, the uniformity was calculated as Petri factor. The evenly spaced array resulted the most uniform light intensity pattern in the simulation, and the Petri factor of 32 and 42 mm of the distances showed higher than 0.9, which represents the ideal uniformity of LED device. The bacterial population of the rice cake decreased to less than the initial bacterial population during exposure to LED blue light, whereas the bacterial population of the control sample increased. The bacterial count of the rice cake after blue light irradiation for 24 h was 1.21 log CFU/g lower than the control sample. Petri factor increased with increase of the distance between the light source and sample, however, the reduction rate of B. cereus group decreased. Therefore, the design of LED device, that represented the Petri factor higher than 0.9 and inactivated the population of B. cereus group, with evenly spaced and 32 mm of distance between the light source and sample was suitable for extending shelf-life of rice cake.

• Horticultural Science & Technology
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• v.31 no.1
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• pp.56-64
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• 2013

Recent unusual weather due to global warming causes shortage of daily sunlight and constitutes one of the primary reasons for agricultural damages. LED light sources are frequently utilized to compensate for the shortage of sunlight in greenhouse agriculture. The present study is aimed at evaluating formations of phytochemicals as well as growth characteristics of mature strawberry fruits ('Daewang' cultivar) during cultivation in a closed growth chamber equipped with artificial LED light as a sole light source. Each LED light of blue (448 nm), red (634 and 661 nm) or mixed blue plus red (blue:red = 3:7) was separately supplied and the intensity of each light was adjusted to $200{\pm}1{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ at plant level with a photoperiod consisted of 16 hours light and 8 hours darkness. Strawberries grown under mixed LED light of blue and red wavelengths showed a higher production of fruits than those grown under other LED treatments. Fructose, one of the free sugars, increased in mixed LED light-grown fruits. Anthocyanin contents were elevated remarkably in the mixed LED light-grown fruits compared with those in other LED treatments. Contrastingly, contents of total phenolics and flavonoids were not of much different from one another among the fruits treated with various LED lights. On the other hand, ripening of strawberry fruits was found to be faster when grown under blue LED light compared with other LED treatments. Moreover, antioxidant activities of blue or red LED light-grown fruits, respectively, were significantly higher than those of mixed LED light-grown fruits. We suggest that when daylight is in shortage during cultivation in a greenhouse, supplementation of sunlight with LED light, which is composed of blue and red wavelengths, could be useful for the enhancement of productivity as well as of free sugar content in strawberry fruits. In addition, for the strawberry culture in the plant factory, selective adoption of LED light wavelength would be required to accomplish the purpose of controlling fruit maturation time as well as of enhancing contents of sugars and antioxidants of fruits.

• Journal of the Korean Vacuum Society
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• v.12 no.4
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• pp.235-238
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• 2003

Conventional LED displays use pixels which consist of red, green and blue LEDs of different operation voltages and degradation characteristics. Thus, the circuits are complicated and the display of each color changes independently with the operated time. In order to solve these drawbacks, an LED chip of a short wavelength and an LED lamp with the mixture of red, green, blue fluorescencers and epoxy on the LED chip were studied. The fluorescencers are excited by the light of the LED chip. The LED chip has an active layer of InGaN, a peak wavelength of 408 nm, a FWHM of 13 nm and the CIE index of (0.198, 0.087). White LED lamps were obtained and the CIE index change was observed with the change of the epoxy amount added to the fluorescencers.

• Horticultural Science & Technology
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• v.32 no.6
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• pp.794-802
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• 2014

The aim of this study was to determine the effect of day-length extension treatment using LED lighting (blue, green, red, or 3 mixed) on vegetative growth and flowering of freesia 'Yvonne', in comparison to that using glow lamps and metal halide lamps. Lighting treatments were imposed from 5 PM to 8 PM for 150 days from after flower bud differentiation to flowering end. For the period from leaf emergence to floral bud formation, no light source affected plant height but the number of leaves was decreased by the metal halide lamp. The highest SPAD value in the flower bud developing period occurred in the metal halide lamp treatment. The time of flowering was advanced by blue or green LED treatment compared to the no lighting control. The green LED lighting advanced flowering by 6 and 8 days compared to no lighting and metal halide lamp treatment, respectively. The blooming period tended to be shortened by the red LED treatment. As for the flower characteristics of 'Yvonne', floret length and width, and the weight of cut flowers were highest in the metal halide lamp treatment. Red LED decreased corm width and weight of 'Yvonne' while glow lamp decreased height and weight. Starch contents in corm were not influenced by the lighting source. Our results indicate that the green LED lighting advanced the time of flowering and the metal halide lamp was good for cut-flower quality.

• Korean Journal of Optics and Photonics
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• v.25 no.4
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• pp.216-220
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• 2014

We have synthesized a $CaMgSi_2O_6:Eu^{2+}$ blue phosphor via a solid-state reaction method. The $CaMgSi_2O_6:Eu^{2+}$ phosphor has monoclinic structure with a space group of C2/c (15), and an emission band peaking at 450 nm (blue) due to the $4f^7-4f^65d$ transition of the $Eu^{2+}ion$. The emission intensity at $100^{\circ}C$ is 54% of the value at room temperature. A white LED was fabricated by integrating a UV LED (400 nm) with our blue phosphor plus two commercial green and red phosphors. The white LED shows a color temperature of 3500 K with a color rendering index of 87 (x = 0.3936, y = 0.3605), and a luminous efficiency of 18 lm/W. The white LED shows a luminance maintenance of 97% after operation at 350 mA for 400 hours at $85^{\circ}C$.

• Korean Journal of Plant Tissue Culture
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• v.27 no.1
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• pp.71-75
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• 2000

To clarify the possibility of plant production under red, green. blue, and red+blue using light emitting diodes (LEDs) and fluorescent lamps (control), the effects of light quality on the growth and morphogenesis of in vitro seedlings in Piatycodon grandiflorum were examined. The plantlets grown under the LEDs resulted in taller plants with greater stem than fluorescent lamps. The shortest shoot length, 3.8 cm, was observed in the control and the longest one, 13.4 cm, in the red light. But the shoot length was 5.6 cm under red LED with supplemental blue(red+blue light). This results indicate that red LED may be suitable, in proper combination with other wavelengths of light. The root length under red light was significantly smaller among the treatments. The plantlets grown under red+blue light had lower shoot dry weight, higher dry matter than other lights-grown plantlets. Among the various growth parameters measered, there was an indication that leaf area was controlled by the LEDs. Leaf area of a plantlets developing under green light was about 2.4 times wider than that of plantlets grown under red LED (10.1 $\textrm{cm}^2$ in area). The dry matter rate per plantlet among the treatments was greater in plantlets grown under the red/blue LEDs in comparison with that grown under other LEDs. Chlorophyll contents in plantlets grown under the red, green, blue and red/blue LEDs were 2%, 7% 20% and 10% lower, respectively, than those in plant grown under fluorescent lamps.

• Korean Journal of Optics and Photonics
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• v.18 no.2
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• pp.155-161
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• 2007

A new and simple method of 3-dimensional circuit modeling and analysis is proposed and verified experimentally for the first time by determining 3-dimensional current flow and 2-dimensional light distribution in blue InGaN/GaN multi-quantum well (MQW) light emitting diode (LED) devices. Circuit parameters of the LED consist of the resistance of the metallic film and epitaxial layer, and the intrinsic diode which represents the active region emitting the light. The circuit parameters are extracted from the transmission line model (TLM) and current-voltage relation. We applied the >> proposed method and extracted circuit parameters to obtain the light emission pattern in a top-surface emitting-type LED. The current spreading effect is analyzed theoretically and quantitatively with a variation of the resistance of metallic and epitaxial layers. The emitting-light distribution of the fabricated blue LED showed a good agreement with the analyzed result, which shows the dark emission intensity at the corner of the p-electrode.