• Journal of Biosystems Engineering
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• v.39 no.2
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• pp.87-95
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• 2014

Purpose: The purpose of this study was to design a variable frequency LED light system for plant factory which combined red, blue, green, white, and UV lights and controlled the ratio of the light wavelength. In addition, this study evaluated the performance of each combination of LED to verify the applicability. Methods: Four combinations of LED (i.e. Red+Blue, Red+Blue+Green, Red+Blue+White, Red+Blue+UV) were designed using five types of LED. The system was designed to control the duty ratio of each wavelength of LED by 1% interval from 0~100%, the pulse by 1Hz interval from 1~20kHz. Response characteristics of the control system, spectral distribution of each combination, light uniformity and uniformity ratio were measured to test the performance of the system. Results: Clean waveforms were measured from 10Hz to 10kHz regardless of duty ratio. Frequency distortion was observed within 5% of inflection point at frequencies above 10kHz regardless of duty ratio, but it was judged negligible. Spectra showed a normal distribution, and maximum PPF with duty ratio of 100% was $271.4{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$ for the Red+Blue combination. PPF of the Red+Blue+Green combination was $258.9{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$, and that of the Red+Blue+White combination was $273.9{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$. PPF of the Red+Blue+UV combination was $267.7{\mu}mol{\cdot}m^{-2}{\cdot}s^{-1}$. Uniformity ratio for the area excepting border showed 0.90 for the Red+Blue and Red+Blue+White combinations, 0.87 for the Red+Blue+Green combination, and 0.88 for the Red+Blue+UV combination. The light was irradiated evenly at the area excepting border, so it was suitable for plant growing. Conclusions: From the results of this study, response characteristics of the control system, spectral distribution of each combination, light uniformity and uniformity ratio were suitable for applying into the plant factory.

• Journal of Life Science
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• v.29 no.3
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• pp.311-317
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• 2019

To investigate the effects of light on growth in fish, olive flounder (Paralichthys olivaceus) were reared under four kinds of monochromatic light-emitting diodes (LEDs) at violet (400 nm), blue (465 nm), green (508 nm), and red (635 nm) wavelengths, along with a white fluorescent lamp as control. The rearing experiments were carried out with 15 fish per tank under different wavelength illumination at the same intensity. After rearing the fish under a 12 hr:12 hr light:dark photoperiod for 60 days, percentage increases in weight gain of $269.92{\pm}13.02$, $363.21{\pm}3.74$, $433.22{\pm}4.83$, $290.17{\pm}11.83$, and $340.74{\pm}26.58%$ and increases in specific growth rates (SGR) of $2.18{\pm}0.06$, $2.56{\pm}0.07$, $2.79{\pm}0.01$, $2.27{\pm}0.05$, and $2.47{\pm}0.10$ were observed in fish grown under the illumination of red, blue, green, and violet LEDs and the white fluorescent light, respectively. The results show faster growth in fish reared under green LEDs, but slower growth in those reared under red light. Differences in most blood parameters were minor, aside from an increased level of glutamic oxaloacetic transaminase in the fish grown under red LED illumination. Histological analysis of the retina showed few changes in the ratio of photoreceptor layer thickness to total retina thickness in fish reared under the green LEDs compared to those in other illumination groups. These results indicate that green LED light can foster increased growth in olive flounder with no distinct harmful effects on their light-sensitive photoreceptor layers.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.11a
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• pp.77-78
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• 2006

In order to increase the efficiency of LED, transparent electrodes should be also developed. also suitable anti-reflection coating (ARC) is necessary for practical device applications. In our paper, Al-doped ZnO (AZO) films were fabricated by sputtering on GaP substrate(wavelength:620nm). Choosing optimum substrate temperature and sputtering rate, high quality AZO films were formed. We confirmed that the surface and electrical properties, which implemented using the methods of AFM, Hall measurement. The properties of AZO thin films especially depended on the thickness. We presumed that the change of the increase the external quantum efficiency of LED according to the AZO thin film of thickness.

• Korean Journal of Optics and Photonics
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• v.24 no.2
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• pp.64-70
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• 2013

In this paper, two white light emitting diodes(LEDs) were manufactured by using two kinds of yellow phosphor, YAG:Ce and $(Sr,Ba)_2SiO_4:Eu$, and their spectroscopic properties were compared and analyzed. We found that the asymmetric double sigmoidal function can be applied to both white LEDs to obtain the center wavelength, the half width, and the skewness parameters. According to this analysis, the half width of the emitting spectrum of silicate phosphor was smaller than that of YAG phosphor, indicating smaller color rendering index. However, the silicate phosphor exhibited better color stability depending on the driving current than the YAG phosphor. The current dependence of the luminous efficacy of both white LEDs was investigated, which showed that efficacy decreased monotonically with current. The efficacy of the silicate-based white LED was lower than that of the YAG-based LED by about 10~12 lm/W.

• Journal of Sensor Science and Technology
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• v.2 no.1
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• pp.75-80
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• 1993

This study describes a non-invasive optical sensor and system in order to obtain oxygen saturation of blood, in-vitro. The sensor contains LED 665nm and 805nm of wavelength for light source and PIN photodiode for light detector in flat pack. The sensor system for measurement of oxygen saturation has breadboarded, including signal amplifier, filter, displayer, A/D converter, microprocessor and memory. Experimental set-up for non-invasive measurement of oxygen saturation in-vitro was done. When the variation of oxygen saturation is compared with that of each wavelength, the variation of 665nm is more than that of 805nm by five times. As oxygen saturation varies from 100% to 60%, and the reflection ratio (R805/R665) is changed linearly. The oxygen saturation in $100%{\sim}60%$ range can be measured with about 5% resolution by the developed sensor, such that if this sensor connects with the main artery and vein, the artificial heart can be controlled rapidly and precisely from measurement of the sensor.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.2
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• pp.221-227
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• 2021

Recently, interests in mask-type skin care devices using light-emitting diodes have been increasing and optical stimuli at certain wavelengths have been known to have various therapeutic effects, such as skin whitening, acne treatment, elasticity and wrinkle improvement by controlling the exposure to wavelengths of light and irradiation time. In particular, light sources of different wavelengths are applied in masks for the purpose of suppressing skin aging, inducing cell proliferation, and alleviating skin inflammation. In this paper, we developed a light-emitting diode control system that is actively used in skin regeneration masks using a microcontroller. Optical stimuli with different manners were applied to skin fibroblast cells in a single or complex wavelengths, and then confirmed how they are effective in the cell differentiation. In addition, we found a specific wavelength that has a positive effect on cell proliferation rates, and confirm the effectiveness of cell proliferation by image processing based quantitative analysis.

• Korean Journal of Environmental Agriculture
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• v.30 no.4
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• pp.402-408
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• 2011

BACKGROUND: Effect of various light wavelength and plant defense molecules were evaluated on the hardness and the contents of free amino acid including ${\gamma}$-aminobutyric acid (GABA) in soybean sprouts. METHODS AND RESULTS: Germinating soybean seeds were treated with various single wavelength of light (380, 440, 470, and 660 nm) or without light at $25^{\circ}C$ for six days. Soybean seeds were also treated with stress-signaling molecule ethephon or $H_2O_2$ at the same time. Soybean sprouts treated with 470 nm substantially raised the hardness almost two times than the control. The free amino acid contents were higher in 470 nm and $H_2O_2$ treated soybean seeds than the control. Nutritionally beneficial GABA contents were increased by the treatments of 470 nm, 440 nm, ethephon, and $H_2O_2$. CONCLUSION: These results suggest that the hardness and the contents of amino acids can be regulated by stimuli, which stimuli could be composed of various wavelength and plant defense molecules. Especially, single wavelength 470 nm illumination has the effect of increasing GABA contents with increased hardness.

• Restorative Dentistry and Endodontics
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• v.35 no.5
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• pp.368-373
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• 2010

Objectives: This study investigated the effect of infection control barrier thickness on power density, wavelength, and light diffusion of light curing units. Materials and Methods: Infection control barrier (Cleanwrap) in one-fold, two-fold, four-fold, and eightfold, and a halogen light curing unit (Optilux 360) and a light emitting diode (LED) light curing unit (Elipar FreeLight 2) were used in this study. Power density of light curing units with infection control barriers covering the fiberoptic bundle was measured with a hand held dental radiometer (Cure Rite). Wavelength of light curing units fixed on a custom made optical breadboard was measured with a portable spectroradiometer (CS-1000). Light diffusion of light curing units was photographed with DSLR (Nikon D70s) as above. Results: Power density decreased significantly as the layer thickness of the infection control barrier increased, except the one-fold and two-fold in halogen light curing unit. Especially, when the barrier was four-fold and more in the halogen light curing unit, the decrease of power density was more prominent. The wavelength of light curing units was not affected by the barriers and almost no change was detected in the peak wavelength. Light diffusion of LED light curing unit was not affected by barriers, however, halogen light curing unit showed decrease in light diffusion angle when the barrier was four-fold and statistically different decrease when the barrier was eight-fold (p < 0.05). Conclusions: It could be assumed that the infection control barriers should be used as two-fold rather than one-fold to prevent tearing of the barriers and subsequent cross contamination between the patients.

• Journal of Conservation Science
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• v.34 no.2
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• pp.77-85
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• 2018

In order to understand the influence of light artifact discoloration, priority must be given to the reaction characteristics of the light the materials constituting the product. In this study, we focus on two representative medium, animal glue and linseed oil which constitute the colored layer of the painting relics. This study is based on an accelerated degradation test using two types of light emitting diods (LEDs) with different wavelength characteristics. In the experiments, discoloration appeared markedly in the animal glue and linseed oil under accelerated aging test conditions using Blue LED. Among the two types of LEDs, the degree of discoloration of the material was much higher with the Blue LED having the total radiation flux (mW). This indicates that the discoloration of painting artifacts such as animal glue and linseed oil is more significantly influenced by the total radiation flux (mW) of the light source than the total luminous flux (lm).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1514-1519
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• 2009

We fabricated the GaNLED emitting 400 nm wavelength and improved the optical extraction efficiency by making surface patterns on n-GaN layer and ITO layer above p-GaN. In addition, the light reflection metal under the n and p pad is made and the light reflection metal is installed on the backside of the chip. The light extraction efficiency is increased by 20 % with texturing n-GaN layer and 18% with texturing ITO layer at 20 mA. Compared to planar-surface LED, the light extraction efficiency for surface texturing both n-GaN and ITO is increased by 32% at 20mA.