• Korean Journal of Optics and Photonics
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• v.30 no.3
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• pp.101-105
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• 2019

An LCD backlight unit (BLU) using RGB light sources is designed and simulated, in order to improve its optical energy efficiency. A color-matching BLU is designed with a lenticular lens array (LLA) with elements that image the linear RGB light sources onto the RGB subpixels of the color filter. Type-A and Type-B simulations are performed, according to the location of the light sources. As a result, the luminance increases to 210% in Type-A and 270% in Type-B respectively. The optimum values for the height and the gap of the LLA for maximum efficiency are found to be $25{\mu}m$ and $3{\mu}m$ respectively.

• Journal of Advanced Engineering and Technology
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• v.6 no.2
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• pp.121-124
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• 2013

This paper proposed a new concept of estimating method for LED(light-emitting diode) delamination with high accuracy. Usually, The LED is composed several materials which are LED chips, gold wire, phosphor, epoxy resin, adhesive, reflector and lead frame. These different materials are usually delaminated in a trouble conditions which are huge temperature difference, hot and humid or mechanical shocked. When the components are delaminated, a luminance will be lost, moisture be absorbed easily and a thermal resistance be increased attendantly. As a conventional method to estimate a delamination of LEDs, a solution immersing method is usually used in a field of LED manufacturing companies or researching institutes. This method has an advantage of simplicity but it is only shown that the existence of delamination or not. In this paper, we have proposed an estimating method for LEDs delamination using the polishing and the electron microscope. New proposed method has shown the result of confirming delamination without destruction and enabled quantitative analysis for LED delamination.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.37 no.3
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• pp.309-313
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• 2024

The key to determining the lifetime of OLED device is how much brightness can be maintained. It can be said that there are internal and external causes for the degradation of OLED devices. The most important cause of internal degradation is bonding and degradation in the excited state due to the electrochemical instability of organic materials. The structure of OLED modeled in this paper consists of a cathode layer, electron injection layer (EIL), electron transport layer (ETL), light emission layer, hole transport layer (HTL), hole injection layer (HIL), and anode layer on a glass substrate from top to bottom. It was confirmed that the temperature generated in OLED was distributed around the maximum of 343.15 K centered on the emission layer. It can be seen that the heat distribution generated in the presented OLED structure has an asymmetrically high temperature distribution toward the cathode, which is believed to be because the sizes of the cathode and positive electrode are asymmetric. Therefore, when designing OLED, it is believed that designing the structures of the cathode and anode electrodes as symmetrically as possible can ensure uniform heat distribution, maintain uniform luminance of OLED, and extend the lifetime. The thermal distribution of OLED was analyzed using the finite element method according to Comsol 5.2.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.2
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• pp.117-128
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• 2001

In order to achieve optimal retrieval, i.e., to find the best match to a query according to a certain similarity measure, the exhaustive search should be performed literally for all the images in a database. However, the straightforward exhaustive search algorithm is computationally expensive in large image databases. To reduce its heavy computational cost, this paper presents a fast exhaustive multi-resolution search algorithm based on image database clustering. Firstly, the proposed algorithm partitions the whole image data set into a pre-defined number of clusters having similar feature contents. Next, for a given query, it checks the lower bound of distances in each cluster, eliminating disqualified clusters. Then, it only examines the candidates in the remaining clusters. To alleviate unnecessary feature matching operations in the search procedure, the distance inequality property is employed based on a multi-resolution data structure. The proposed algorithm realizes a fast exhaustive multi-resolution search for either the best match or multiple best matches to the query. Using luminance histograms as a feature, we prove that the proposed algorithm guarantees optimal retrieval with high searching speed.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.34 no.1
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• pp.185-194
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• 2014

This study investigates the methodology to evaluate the quantified performance of pavement markings and traffic guide signs using digital images. This methodology is significant to attempt to quantify their performance without large brightness photometer at the nighttime and bad weather. The retroreflective performance of pavement markings are evaluated through the contrast of gray levels of pavements and markings in collected digital images under the case of rain, dampness, and dryness. In addition, the appraisal of retroreflective performance of traffic guide signs are implemented through the comparison between interior illuminated and the existing retroreflective traffic guide signs using the contrast of luminance extracted from the value of RGB of backgrounds and legends in collected digital images according to geometric design, driving lanes, and the distance between the car and the sign. As a result, the retroreflective performance of pavement markings deteriorates about 3.5 times and 2 times under the case of rain and dampness respectively than dryness. Also, the performance of the existing traffic guide signs is significantly influenced by geometric design, driving lanes, and the distance, otherwise interior illuminated traffic guide signs. This methodology can be utilized to construct objective information of performance of traffic safety facilities to select appropriate position of expensive high reflective pavement markings and interior illuminated traffic guide signs considering diverse weather and geometric design.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.38 no.3
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• pp.258-268
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• 2001

The compression method is necessarily used to send the high quality moving picture that contains a number of data in image processing. In the field of moving picture compression method, the motion estimation algorithm is used to reduce the temporal redundancy. Block matching algorithm to be usually used is distinguished partial search algorithm with full search algorithm. Full search algorithm be used in this paper is the method to compare the reference block with entire block in the search window. It is very efficient and has simple data flow and control circuit. But the bigger the search window, the larger hardware size, because large computational operation is needed. In this paper, we design the full search block matching motion estimator. Using the DCT DC values, we decide luminance. And we apply 3 bit compare-selector using bit plane to I(Intra coded) picture, not using 8 bit luminance signals. Also it is suggested that use the same selective bit for the P(Predicted coded) and B(Bidirectional coded) picture. We compare based full search method with PSNR(Peak Signal to Noise Ratio) for C language modeling. Its condition is the reference block 8$\times$8, the search window 24$\times$24 and 352$\times$288 gray scale standard video images. The result has small difference that we cannot see. And we design the suggested motion estimator that hardware size is proved to reduce 38.3％ for structure I and 30.7％ for structure II. The memory is proved to reduce 31.3％ for structure I and II.

• Korean Journal of Materials Research
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• v.33 no.1
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• pp.15-20
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• 2023

'Tracers' are bullets that emit light at the backside so that the shooter can see the trajectory of their flight. These light-emitting bullets allow snipers to hit targets faster and more accurately. Conventional tracers are all combustion type which use the heat generated upon ignition. However, the conventional tracer has a fire risk at the impact site due to the residual flame and has a by-product that can contaminate the inside of the gun and lead to firearm failure. To resolve these problems, it is necessary to develop non-combustion-type tracers that can convert heat to luminance, so-called 'thermoluminescence (TL)'. Here, we highly improve the thermoluminescence properties of MgB₄O₇ through co-doping of Dy³⁺+Ce³⁺ and Dy³⁺+Na⁺. The presence of doping materials (Dy³⁺, Ce³⁺, Na⁺) was confirmed by XPS (X-ray photoelectron spectroscopy). The as-synthesized co-doped MgB₄O₇ was irradiated with a specific radiation dose and heated to 500 ℃under dark conditions. Different thermoluminescence characteristics were exhibited depending on the type or amounts of doping elements, and the highest luminance of 370 cd/m² was obtained when Dy 10 % and Na 5 % were co-doped.

• Journal of the Korean Vacuum Society
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• v.16 no.5
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• pp.330-337
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• 2007

Influence of glass dielectric property (dielectric constant K, dielectric loss) on the external electrode fluorescent lamps of the dielectric barrier discharge has been investigated with 4-different glasses. Conventional borosilicate glass tubes with $K=5.6{\sim}5.9$ and tan ${\delta}=5.0{\times}10^{-3}{\sim}6.0{\times}10^{-3}$ and aluminosilicate glass tubes with high K=6.6 and low tan ${\delta}=1{\times}10^{-4}$ and soda-lime glass tribes with K=7.7 and tan ${\delta}=1.37{\times}10^{-2}$ have been compared. The high value of dielectric constant K makes the capacitance of external electrode fluorescent lamps intensity and enhances the discharge efficiency. The dielectric loss of tan ${\delta}$ shows the factor of power consumption in the external electrode to induce heats and to be weak in pinhole stability. The aluminosilicate glass tubes of high K and low tan ${\delta}$ have been enhanced by $14{\sim}18%$ in luminance and efficiency in comparison with the conventional borosilicate glass tubes and the aluminosilicate external electrode fluorescent lamps are strong against the pinhole formation. Soda-lime glass tubes with high K and high tan ${\delta}$ are a little favorable in luminance and efficiency and they are very weak in pinhole occurrence.

• Progress in Medical Physics
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• v.27 no.2
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• pp.98-104
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• 2016

We investigated the effect of high dose on the sensitivity of optically stimulated luminance dosimeters (OSLDs) on Co-60 gamma rays and used a commercial OLSD (Landauer, Inc., Glenwood, IL). New OSLDs were chosen arbitrarily and were irradiated with 1 Gy repeatedly. We confirmed the change in the radiation sensitivity after repeated irradiation. The OSLD sensitivity increased up to 3% after irradiating for seven times and decreased continuously after the eighth time. It dropped by approximately 0.35 Gy per irradiation. Finally, after irradiating for 30 times, the OSLD sensitivity decreased by approximately 7%. When the OSLDs were irradiated 10 times with 1 Gy after their irradiation using a high dose of 15 Gy and 30 Gy, their sensitivity decreased by 6% and 12%, respectively, compared to that before high-dose irradiation. The change in the OSLD sensitivity with a high dose could be modeled by an exponential equation. We confirmed the radiation sensitivity variation caused by a high dose, and the irradiation history of dosimeters was considered to reuse OSLDs irradiated with a high dose.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.5
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• pp.147-154
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• 2015

In this paper, we employed a model which defines the sensitivity according to the background luminance, so called JND (Just Noticeable Difference), and applied to the video coding. The proposed method finds out the maximum possible quantization parameter for the current unit based on the threshold of JND model and reduce the bitrate with similar perceptual quality. It selects the higher quantization parameter and reduce the bitrate when the reconstructed signal which is coded with higher quantization parameter is in a range of allowance based on the JND threshold, i.e. the signal has the similar perceptual quality compared to that is coded with the initial quantization parameter. The proposed algorithm was implemented on HM16.0, which is a reference software of the latest video coding standard HEVC (High Efficiency Video Coding) and the coding performance was evaluated. Compared to HM16.0, the proposed algorithm achieved maximum 20.21% and 6.18% of average bitrate reduction with the similar perceptual quality.