• Title/Summary/Keyword: Luminance deviation

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A Study on How to Minimize the Luminance Deviation of AC-LED Lighting (교류 LED 조명의 빛 밝기 편차를 최소화하는 방법에 대한 연구)

  • Dong Won Lee;Bong Hee Lee;Byungcheul Kim
    • Journal of the Korean Institute of Electrical and Electronic Material Engineers
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    • v.36 no.3
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    • pp.255-260
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    • 2023
  • In order to spread LED lighting, LED lighting technology directly driven by alternating current (AC) commercial power has recently been introduced. Since current does not flow at a voltage lower than the threshold voltage of the LED, a non-conductive section occurs in the current waveform, and the higher the threshold voltage of the LED, the more discontinuous current waveforms are generated. In this paper, multi-LED modules are connected in series so that the threshold voltage can be adjusted according to the number of LED modules. A small number of LED modules are driven at a low instantaneous rectified voltage, and a large number of LED modules are driven at a high instantaneous rectified voltage to lengthen the overall lighting time of AC-LED lighting, thereby minimizing the luminance deviation of AC-LED lighting. In addition, the load current flowing through the LED module is adjusted to be the same as the design current even at the maximum rectified voltage higher than the design voltage, so that the light brightness of the LED module is kept constant. Therefore, even if the rectified voltage applied to the LED module changes, the AC-LED lighting in which the light brightness is constant and the luminance deviation is minimal has been realized.

Luminance Performance of a Room with Light Guide and Blind Systems by Mockup Experiments (혼합형 채광조절장치가 실내공간의 휘도분포에 미치는 영향에 관한 Mockup 실험평가)

  • Shin, Hwa Young;Ahn, Hyun Tae;Kim, Jeong Tai
    • KIEAE Journal
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    • v.7 no.1
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    • pp.65-72
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    • 2007
  • As ecological design elements, daylighting can be applied to provide adequate illumination on visual tasks to create an attractive visual environment and to save electrical energy. Daylighting control systems reject direct sunlight and penetrate it onto the ceiling or to deep into the room. This study aims to evaluate the luminance environment of sloped light guide with automated venetian blind systems according to sun angle changes. For evaluation, a mock-up model was used and the south facing side-window mounted between the clerestory window and the view window. To assess luminance performance, 3 view points of luminance were monitored. As results, the conventional and lightshelves show ideal luminance ratio between workplane and surroundings(3:1) and workplane and darkness area(2:1) due to total ratio of surroundings and darkness area has lower ratio than workplane. Compared to the lightshelves window, conventional window shows unrelieved effect in between the workplane and brightness area(1:5). It means that there has low deviation according to the required standards. Also, compared to the ratio between the brightness area and darkness area(2~6:1) conventional window with high deviation(10~20:1) provide discomfort glare due to the excessively strong contrast, while lightshelves window shows a required luminance ratio that provide a three-dimensional effect to occupants. Therefore, luminance distribution indicate that application of a lightshelves and blinds not only has a significantly positive effect but also offers higher luminance quality in a daylit room

A Model of Pupil's Change with Luminance (Luminance에 의한 Pupil의 변화에 대한 모델)

  • Kim, Yong-Geun
    • Journal of Korean Ophthalmic Optics Society
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    • v.1 no.2
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    • pp.7-11
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    • 1996
  • The size of pupil with pupillary light reflex is determined by the amount of a luminance. and it is dependent with the distribution function of the retinal illuminance which is the amount of transmittance for the external light due to the size of pupil, and the detector of cone and rod due to the amount of the luminance. The change of the pupil size with the luminance can be expressed with the mathematical model $$y(x)={\alpha}+{\beta}\frac{1}{1+{e}{x}{p}(x-x_0)/{\theta}}$$ where ${\alpha}$ is the size of the pupil diameter in a maximum value of the luminance, ${\beta}$ is the deviation of the pupil's diameter between maximum and minimum, ${\theta}$ is the parameter showed the degree of a sensitivity. Comparing with the experimental value of P.Moon et al, We known that the equation of the model is very compatible.

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Measurement of MRI Monitor Luminance and MRI Room Illuminance with a Light Probe (Light Probe를 이용한 MRI 검사실 및 모니터의 조도와 휘도 측정)

  • Kim, Ji Min;Han, Ah Yung;Lee, Ha Young;Lee, So Ra;Kweon, Dae Cheol
    • Journal of the Korean Magnetics Society
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    • v.26 no.5
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    • pp.168-172
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    • 2016
  • The purpose of the optimal environment of the MRI room to measured luminance and illuminance of the MRI room and the monitor. University Hospital (n = 6) of the MRI (n = 10) in the luminance and illuminance Light Probe Xi Unfors (Unfors Instruments AB, Billdal, Sweden) was measured by using the. Black luminance level and white level of illuminance is repeated three times in the middle of the side of the monitor to obtain the mean and standard deviation using a t-test statistical processing was of significance test. Monitor luminance and black level in the average $1.78cd/m^2$, the standard deviation was $0.85cd/m^2$, white level average of $43.58cd/m^2$, the standard deviation of $13.19cd/m^2$. Illuminance of MRI room was the lowest value measured in accordance with the 30.5 lux, the maximum value is 601.3 lux, mean was measured by a variety of 177.86 lux. Luminance and illuminance of the MRI room and monitor is found to have statistically significant difference (p < .05). In conclusion, refer to the recommended standard of MRI and room monitor luminance and illuminance and to create an optimal environment.

A Study on Luminance Contrast Criteria for Tactile Walking Surface Indicators (시각장애인 점자블록의 휘도대비 기준에 대한 연구)

  • Shin, Dong-Hong;Park, Kwang-Jae;Kim, Sang-Woon
    • Journal of The Korea Institute of Healthcare Architecture
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    • v.22 no.1
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    • pp.7-15
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    • 2016
  • Purpose: There are the number of color tactile walking surface indicators installed in Korea, because of indefinite regulation in blind and vision-impaired persons' tactile walking surface indicators. In case of yellow tactile walking surface indicators, it shows a deviation severe color. In this study, the researchers suggested color and brightness reference for helping blind and vision-impaired persons' walking through analyzing the color references of tactile walking surface indicators and the color luminance between tactile walking surface indicators and sidewalk currently used. Method: Reasonable luminance contrast criteria is suggested by examining ways of improving the recognition and recognition of objects according to color contrast visually impaired through literature review and analyzing standards of tactile walking surface indicators and the Europe, Japan and Australia of color and luminance contrast criteria. And by examining the color of the tactile walking surface indicators reported in Korea currently used to derive the problem presented by the luminance contrast in the reference and comparison. Finally, the visually impaired tactile walking surface indicators is set for color selection criteria for the recognition rate improves. Results: In order to improve the recognition rate to be tactile walking surface indicators of the contrast of the visually impaired and the environment than the color of the tactile walking surface indicators itself to secure always a certain level or more of brightness contrast values in the set of the color of the tactile walking surface indicators so important. Implication: In order to set the blind tactile walking surface indicators color recognition based on the verification of the real pedestrian based on the results presented in this paper it is required. It is to be understood as an element of the barrier free configuration for securing the walking pedestrian safety.

The Acceptance Testing of 5 Mega Pixels Primary Electronic Display Devices and the Study of Quality Control Guideline Suitable for Domestic Circumstance (5 Mega 화소 진단용 전자표시장치 인수검사 및 국내 실정에 적합한 정도관리 가이드라인 연구)

  • Jung, Hai-Jo;Kim, Hee-Joung;Kim, Sung-Kyu
    • Progress in Medical Physics
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    • v.18 no.2
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    • pp.98-106
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    • 2007
  • In June 2005, Yonsei University Medical Center, Severance Hospital upgraded a full-PACS system by adding twenty (5 mega pixels) Totoku ME511L flat panel LCD display devices for diagnostic interpretation purposes. Here we report upon the quantitative (or visual) acceptance testing of the twenty Totoku ME511L display devices for reflection, luminance response, luminance spatial dependency, resolution, noise, veiling glare, and display chromaticity based on AAPM TG 18 report. The tools used in the tests included a telescopic photometer, which was used as a colorimeter, illuminance meter, light sources for reflection assessment, light-blocking devices, and digital TG18 test patterns. For selected 8 flat panel displays, mean diffuse reflection coefficient ($R_d$) was $0.019{\pm}0.02sr^{-1}$. In the luminance response test, luminance ratio (LR), maximum luminance difference ($L_{max}$), and deviation of contrast response were $550{\pm}100,\;2.0{\pm}1.9%\;and\;5.8{\pm}1.8%$, respectively. In the luminance uniformity test, maximum luminance deviation was $14.3{\pm}5.5%$ for the 10% luminance of the TG18-UNL10 test pattern. In the resolution test with luminance measurement method, percent luminance (${\Dalta}L$) at the center was $0.94{\pm}0.64%$. In all cases of noise testing, rectangular target In every square in the three quadrants was visible and all 15 targets except the smallest one in the every corner pattern and the center pattern. The glare ratio (GR) was $12,346{\pm}1,995$. The color uniformity, (u',v'), was $0.0025{\pm}0.0008$. Also, the research results of qualify control guideline of primary disply devices suitable for domestic circumstance are presented All test results are in-line with the criteria recommended by AAPM TG18 report and are thus fully acceptable for diagnostic image interpretation. As a result, the acceptance testing schedule described provides not only an acceptance standard but also guidelines for quality control, optimized viewing conditions, and a means for determining the upgrading time of LCD display devices for diagnostic interpretation.

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Assessment of LCD Color Display Performance Based on AAPM TG 18 Protocol : Decision of Quality Control and Calibration Period (판독용 LCD 컬러 모니터 장치의 성능 평가 - 성능 평가 및 Calibration 주기 결정을 중심으로 -)

  • Lee, Won-Hong;Son, Soon-Yong;Noh, Sung-Soon;Lee, In-Hwa;Kang, Sung-Ho;Lee, Yong-Moon;Park, Jae-Soo;Yoon, Seok-Hwan
    • Journal of radiological science and technology
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    • v.31 no.1
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    • pp.55-60
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    • 2008
  • Purpose: This study is to decide a quality control and calibration period of LCD display devices used for reading diagnostic images. Materias and Methods: The assessment test of 20 flat panel LCD color display devices used for reading diagnostic images were performed based on AAPM TG 18 protocol over the total six sessions at one month intervals from three months after primary calibration, in terms of geometric distortion, reflection test, luminance response evaluation, luminance uniformity, resolution, noise, veiling glare and chromaticity test. Results: The results of geometric distortion, reflection test, luminance uniformity, resolution, noise, veiling glare and chromaticity test were within the criteria recommended by AAPM TG 18, except for luminance response evaluation. In the measured luminance deviation of luminance response evaluation, 4(25%) of 20 display devices were passed a criterion from four months after calibration, and 11 (55%) were passed from eight months. Also in the contrast response of the luminance response evaluation, 1(5%) display device was passed a criterion from four months after calibration, and 3(15%) were passed from eight months. Conclusion: Considering the passing deviation after calibration, the time required and a manpower, the quality control and calibration period of LCD display devices used for reading diagnostic images should be a three months and six months after calibration.

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Influence of Detailed Structure and Curvature of Woven Fabric on the Luminescence Effect of Wearable Optical Fiber Fabric (직물의 세부 구조 및 굴곡이 웨어러블 광섬유의 발광 효과에 미치는 영향)

  • Yang, Jin-Hee;Cho, Hyun-Seung;Kwak, Hwy-Kuen;Oh, Yun-Jung;Lee, Joo-Hyeon
    • Science of Emotion and Sensibility
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    • v.21 no.4
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    • pp.55-62
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    • 2018
  • The two main requirements of wearable optical fiber fabrics are that they must presuppose a high degree of flexibility and they must maintain the luminance effect in both flat and bent conformations. Therefore, woven optical fiber fabrics that satisfy the above conditions were developed by both weaving and by using computer embroidery. First, we measured the brightness of the wearable optical fiber fabric in the flat state at a total of 10 measurement points at intervals of 1 cm. Second, the wearable optical fiber fabric was placed horizontally on the forearm, where three-dimensional bending occurs, and the luminance values were recorded at the same 10 measurement points. For the woven fabric in the flat state, the maximum, minimum, average, and standard deviation luminance values were $5.23cd/m^2$, $2.74cd/m^2$, $3.56cd/m^2$, and $1.11cd/m^2$, respectively. The corresponding luminance values from the bent forearm were $7.92cd/m^2$ (maximum), $2.37cd/m^2$ (minimum), $4.42cd/m^2$ (average), and $2.16cd/m^2$ (standard deviation). In the case of the computer-embroidered fabric, the maximum, minimum, average, and standard deviation luminance values in the flat state were $7.56cd/m^2$, $3.84cd/m^2$, $5.13cd/m^2$, and $1.04cd/m^2$, respectively, and in the bent forearm state were $9.6cd/m^2$, $3.63cd/m^2$, $6.13cd/m^2$, and $2.26cd/m^2$, respectively. Therefore, the computer-embroidered fabric exhibited a higher luminous effect than the woven fabric because the detailed structure reduced light-loss due to the backside fabric. In both types of wearable optical fiber fabric the luminance at the forearm was 124% and 119%, respectively, and the light emitting effect of the optical fiber fabric was maintained even when bent by the human body. This is consistent with the principle of Huygens, which defines the wave theory of light, and also the Huygens-Fresnel-Kirchhoff principle, which states that the intensity of light increases according to the magnitude of the angle of propagation of the light wavefront (${\theta}$).

High Efficiency LED Driving System using Y type Current Balancing Transformer (Y형 전류평형 트랜스포머를 이용한 고효율 LED 구동시스템)

  • Kim, Jin-Gu;Yoo, Jin-Wan;Park, Chong-Yeon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.3
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    • pp.223-231
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    • 2015
  • LEDs have been widely used in lighting displays, automobiles, and airplanes owing to their excellent light output characteristics and long lifespan. Though LEDs are manufactured under the same process, variations in impurity concentrations cause electrical deviation among LEDs. The resulting electrical deviation can not only reduce the life time of the LED but also cause non-uniform luminance of LEDs connected in parallel. LED driving circuit is required to solve these problems. In this paper, we propose a LED driving system using Y-type current balancing transformer to maximize the efficiency of the system by removing output stage Schottky diodes. Experimental results are presented to verify the performance of proposed LED driving system that is applied to 80 W LED modules.

A Study on Illumination Distribution of Blackboard on Elementary, Junior and Senior High School (초.중.고교의 흑판조도분포에 관한 연구)

  • Kim, Dong-Jin;Choi, Jae-Myoung;Kim, Tae-Hyoun;Lee, Hyoun-Jae;Lee, Byoung-Gi;Park, Tong-wha
    • Proceedings of the KIEE Conference
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    • 1998.07e
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    • pp.1770-1772
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    • 1998
  • This study is concluded under by investigation about the lighting environment on a blackboard in elementary, middle, high school of inchon metropolitan. 1. The illumination was approximated to standard value in the side of quantity by the result of the Mimistry of Education's command. However, the uniformity of illuminescence was relatively increased. 2. In order to raise the blackboard lighting, we installed local lighting fixture for blackboard but most of schools are directly adopted to the way of sticking to the blackboard and the lower part of the blackboard is not effective. So that it is desirable of teacher and students to put the local lighting in front of the higher part of the blackboard or install in setting the perfect diffusion light from the ceiling. 3. Deviation of luminance is also more groat when local lighting exist for blackboard. And, regardless of local lighting, luminance of blackboard in side of window, from direction of floor is high because of regular reflected light. Therefore a curtain or blind must be installed pertinently.

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