• Journal of Information Display
• /
• v.11 no.3
• /
• pp.123-127
• /
• 2010

Fluorescent white organic light-emitting diodes showing high color-rendering indices (CRIs) of up to 81 was demonstrated, with a silicon-cored anthracene derivative (PATSPA) doped with DPAVBi utilized as the deep-blue host and dye materials, and the commercial dyes rubrene and DCM2 utilized as the orange- and red-light-emitting dyes. The devices, consisting of three emissive layers, showed bright-white-light emission, but the ratio of the blue peak to the orange and red peaks changed with the current density and the thickness of the blue emissive layer. A high CRI was achieved with the use of a deep-blue emitter doped in a novel host and by optimizing the blue-layer thickness. The device with a blue-layer thickness of 10 nm showed the Commission Internationale de l'Eclairage (CIE) color coordinate of (0.33, 0.35), a high CRI of 81, and a moderate external quantum efficiency of 2% at a current density of $2.5\;mA/cm^2$.

• Science of Emotion and Sensibility
• /
• v.15 no.3
• /
• pp.381-388
• /
• 2012

The purpose of this study is to check if LED lighting can be used as general lighting and examine the color rendering property of full color RGB LED lighting. CRI is one of the important properties of evaluating lighting. However the present CRI does not fully evaluate LED lightings. Firstly, the performance of a simple task was compared other than comparing CRI values for different lighting. For experimental preparation three types of lightings were used; standard D65 fluorescent tube, general household fluorescent tube, and RGB LED lighting. All three lightings show high error for Purple-Red. All three lightings show similar error for all hues and prove that color discrimination is not affected by the lighting. This proves that LED could be used as general lighting. Secondly, problems of the conventional CIE CRI method are considered and new models are suggested for the new lighting source. Each of the models was evaluated with visual experiment results obtained by the white light matching experiment. The suggested model is based on the CIE CRI method but replaces the color space model by CIELAB, color difference model by CIEDE2000, and chromatic adaptation model by CAT02.

• Journal of the Architectural Institute of Korea Planning & Design
• /
• v.35 no.1
• /
• pp.99-106
• /
• 2019

This study aims to recommend the proper Color rendering index (CRI), the Correlated Color Temperature (CCT), and illuminance levels of Light-Emitting Diode (LED) lighting based on the analysis of the criteria of the current CRI, the CCT, and illuminance levels in merchandising spaces with LED lighting conditions. It would be a basic material to apply in line with user preference for LED merchandising lighting. To this end, it examines relevant literature review on the experiments designed to test whether lighting characteristics affect brightness perception, color appearance, and pleasantness. Highly saturated colors appear brighter than low saturated colors. Two lighting applications - grocery and clothing shop - were created in elaborating the effect of LED lighting characteristics of CRI on color appearance and the CCT and illuminance on pleasantness. The findings show that the criteria of CIE Ra<80 are appropriate to provide better color appearance of illuminated products in terms of LED lighting that can enhance color saturation, particularly for the red color. Furthermore, 2700 K and less than 500 lux for grocery, 4000 K and more than 500 lux for clothing shop are found to be the proper the CCT and illuminance levels respectively to bring better preference under LED lighting.

• Current Optics and Photonics
• /
• v.4 no.3
• /
• pp.247-252
• /
• 2020

Important determinants for selecting outdoor lighting are the color-rendering index (CRI) and scotopic-to-photopic (S/P) ratio of the lighting units. The higher the S/P ratio, the better energy savings and visual performance. In this study, CCT-tunable LED lighting units were optimized and fabricated by spectral combination of red, green, blue, and yellow LEDs. The measured results for RGB LEDs provided S/P ratios of 1.55~2.58 and those of RGBY LEDs gave 1.46~2.46 to the correlated color temperatures (CCTs) ranging from 2700 K to 6500 K, with CRI values of over 80 at the same time.

• Current Optics and Photonics
• /
• v.3 no.1
• /
• pp.78-85
• /
• 2019

The remote phosphor structure has been proven to bear greater luminous efficiency than both the conformal phosphor and in-cup phosphor structures; however, controlling its color quality is much more challenging. To solve this dilemma, various researchers have proposed dual-layer phosphor and triple-layer phosphor configuration as techniques to enhance the display brightness of white LEDs (WLEDs). Likewise, this study picked one of these configurations to utilize in multichip WLEDs with five distinct color temperatures in the range from 5600 to 8500 K, for the purpose of improving the optical properties of WLEDs, such as color rendering index (CRI), color quality scale (CQS), luminous efficacy (LE), and chromatic homogeneity. According to the results of this research, the triple-layer phosphor configuration has superior performance compared to other configurations in terms of CRI, CQS, and LE, and yields higher chromatic stability for WLEDs.

• 한국정보디스플레이학회:학술대회논문집
• /
• 2006.08a
• /
• pp.961-965
• /
• 2006

White organic LED spectrum for lighting and displaying should be designed for high luminous efficiency as well as good chromaticity coordinate, pleasant correlated color temperature and color rendering. A program based on Matlab was made to make these calculations convenient. The chromaticity coordinate and luminous efficiency was calculated according to the CIE 1931 colorimetric system, while the correlated color temperature(CCT) was calculated based on CIE 1960 UCS diagram. The color rendering characteristics were evaluated according to the CIE Color Rendering Index (CRI), using Ra, Ri and ${\bigtriangleup}E$ from the 14 color samples defined in CIE13.3.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.24 no.8
• /
• pp.1006-1014
• /
• 2020

Consumer expectations for drama VFX increased as the influx of overseas dramas increased due to the growth of OTT service, but the current production time of the drama production system has a negative effect on the quality and completion of work. This paper proposes a background rendering using a game engine and a subject rendering using background HDRI as environmental lighting. The proposed workflow is expected to reduce the production time of VFX and improve the quality of VFX. The proposed workflow was verified in 3 steps. Comparing game engine and rendering software according to the same lighting environment and camera distance, comparing rendering with existing rendering method and background HDRI generation, and validating the proposed workflow. For verification, quantitative evaluation was performed using Structual similarity index and histogram. This study is expected to be one of the options to improve the quality of VFX and improve the risk.

• Korean Journal of Materials Research
• /
• v.21 no.5
• /
• pp.250-254
• /
• 2011

We have synthesized bluish-green, highly-efficient $BaSi_2O_2N_2:Eu^{2+}$ and $(Ba,Sr)Si_2O_2N_2:Eu^{2+}$ phosphors through a conventional solid state reaction method using metal carbonate, $Si_3N_4$, and $Eu_2O_3$ as raw materials. The X-ray diffraction (XRD) pattern of these phosphors revealed that a $BaSi_2O_2N_2$ single phase was obtained. The excitation and emission spectra showed typical broadband excitation and emission resulting from the 5d to 4f transition of $Eu^{2+}$. These phosphors absorb blue light at around 450 nm and emit bluish-green luminescence, with a peak wavelength at around 495 nm. From the results of an experiment involving Eu concentration quenching, the relative PL intensity was reduced dramatically for Eu = 0.033. A small substitution of Sr in place of Ba increased the relative emission intensity of the phosphor. We prepared several white LEDs through a combination of $BaSi_2O_2N_2:Eu^{2+}$, YAG:$Ce^{3+}$, and silicone resin with a blue InGaN-based LED. In the case of only the YAG:$Ce^{3+}$-converted LED, the color rendering index was 73.4 and the efficiency was 127 lm/W. In contrast, in the YAG:$Ce^{3+}$ and $BaSi_2O_2N_2:Eu^{2+}$-converted LED, two distinct emission bands from InGaN (450 nm) and the two phosphors (475-750 nm) are observed, and combine to give a spectrum that appears white to the naked eye. The range of the color rendering index and the efficiency were 79.7-81.2 and 117-128 lm/W, respectively. The increased values of the color rendering index indicate that the two phosphor-converted LEDs have improved bluish-green emission compared to the YAG:Ce-converted LED. As such, the $BaSi_2O_2N_2:Eu^{2+}$ phosphor is applicable to white high-rendered LEDs for solid state lighting.

• Korean Journal of Materials Research
• /
• v.29 no.7
• /
• pp.437-442
• /
• 2019

Green $BaSi_2O_2N_2:0.02Eu^{2+}$ phosphor is synthesized through a two-step solid state reaction method. The first firing is for crystallization, and the second firing is for reduction of $Eu^{3+}$ into $Eu^{2+}$ and growth of crystal grains. By thermal analysis, the three-time endothermic reaction is confirmed: pyrolysis reaction of $BaCO_3$ at $900^{\circ}C$ and phase transitions at $1,300^{\circ}C$ and $1,400^{\circ}C$. By structural analysis, it is confirmed that single phase [$BaSi_2O_2N_2$] is obtained with Cmcm space group of orthorhombic structure. After the first firing the morphology is rod-like type and, after the second firing, the morphology becomes round. Our phosphor shows a green emission with a peak position of 495 nm and a peak width of 32 nm due to the $4f^65d^1{\rightarrow}4f^7$ transition of $Eu^{2+}$ ion. An LED package (chip size $5.6{\times}3.0mm$) is fabricated with a mixture of our green $BaSi_2O_2N_2$, and yellow $Y_3Al_5O_{12}$ and red $Sr_2Si_5N_8$ phosphors. The color rendering index (90) is higher than that of the mixture without our green phosphor (82), which indicates that this is an excellent green candidate for white LEDs with a deluxe color rendering index.

• Korean Journal of Optics and Photonics
• /
• v.32 no.4
• /
• pp.163-171
• /
• 2021

Conventional white light-emitting diodes (LEDs) for lighting applications consist of blue LEDs and yellow phosphors, the spectrum of which lacks deep red. To improve the color-rendering characteristics of white LEDs, a red quantum-dot film was applied to the diffuser plate of LED lighting. The mean free paths of the quantum dots and the concentration of the TiO₂ particles in the diffuser plate were adjusted to optimize the optical structure of the lighting. The color-rendering index (CRI) was greater than 90 for most conditions, which demonstrates that adoption of the red quantum-dot film is an effective way for improving the color-rendering properties of conventional white LEDs. The angular dispersion of color coordinates could be removed by utilizing the optical cavity formed between the diffuser plate and the reflector on the bottom of the lighting, where multiple passages of the light through the quantum-dot film reduced the differences in optical path length depending on the viewing angle.