CIE Xy Research Articles

Maximum possible contrast level for silent substitution: a theoretical model applied to melanopsin stimulation.

For any given set of light sources stimulating the photoreceptors of the retina, the theoretical levels of illumination producing the smallest and the largest expression of one photoreceptor with fixed stimulation for the others are analytically computed. The cases of four, five, and more light sources are studied. We show that, for contrast optimization, only as many light sources as photoreceptors do matter and that, in the case of four light sources, the maximum contrast achievable for melanopsin lies at the intersection of the lines joining the sources in the CIE xy chromaticity diagram. This result is used to obtain the optimal position of four Gaussian primaries of equal bandwidth. In addition, we derive a procedure to construct level maps for melanopsin contrast overlying the diagram. In the second part of the paper, the interpersonal variability of the perceived stimulation is shown to be globally reduced if the bandwidth of the light sources is increased and, under some assumptions, if a light source is added.

An Experimental Study on Color Shift of Injection-Molded Mobile LGP Depending on Surface Micropattern.

In the display industry, the LCD backlight unit (BLU) module is variously used in mobile phones, notebook computers, monitors, and TVs. The light guide plate (LGP), which is one of the core parts of a BLU, is getting bigger and thinner consistently. Conventional injection methods and injection processes like injection compression molding (ICM) are becoming more complex and harsher with high-speed injection at high mold and melt temperatures. These approaches lead to a change in physical properties and a decrease in optical properties such as yellowing and color shift in injection-molded parts. In the present study, an injection molding experiment was conducted to understand the effect of surface patterns and major injection process conditions like mold and melt temperatures on the color shift in injection-molded mobile LGP. Optical properties obtained by the direct and total transmittance and CIE xy chromaticity diagram for injection-molded mobile LGP were measured with a UV–visible spectrophotometer. From the measurement of patternless LGP, it was found that total or direct transmittance was not affected by molding process variables. It was also found that yellow shift, , occurred as much as 0.00111 ± 0.00014, and a color shift angle, of 43.05 ± 2.44° was recorded in CIE coordinates for all nine experimental cases. From the measurement of total transmittance of patterned LGP, and were found to be almost the same as those of patternless LGP for the locations of low and medium density of the pattern for the LGP, T1 and T2. The measured data of direct transmittance of patterned LGP showed that additional yellow shift due to scattering caused by surface micropattern. Interestingly, of patterned data remained 43.05 ± 2.44°, which was almost the same as that found in the case of patternless LGP.

Chromaticity-based real-time assessment of melanopic and luminous efficiency of smartphone displays.

We investigate the spectral power distributions of 54 phones (33 measured experimentally in default text mode and 21 downloaded from the web) and estimate the mean ± std. dev. of the luminous efficiency of radiation, melanopic efficiency of radiation, and melanopic/photopic ratio as 287 ± 13 lm/W, 303 ± 26 blm/W, and 1.06 ± 0.13, respectively. We establish the chromaticity-performance characteristics relation to precisely assess the action efficiency of radiation performance using either RGB gray values or CIE xy values. Our real-time assessment of smartphone displays can aid in reducing energy consumption and improving user health.

Studies on different primaries for a nearly-ultimate gamut in a laser display.

In using a laser light source, it becomes possible to realize an ultra-wide display gamut that approaches the human color vision limit. This paper introduces a method for extremely large gamut optimization for different primary numbers, and it offers a primary set that produces a nearly ultimate gamut. Considering display lightness, we calculated wavelength selection and lightness design of a display with 3-9 primaries in the CIELAB uniform color space (UCS) by optimizing the coverage of the optimal color gamut. Theoretically the maximum gamut area of a laser display with 3-12 primaries in the CIE xy and CIE u'v' chromaticity diagrams is also calculated for comparison. We recommend 6 primaries as a reasonable choice, since the coverage reaches 97.6% of the optimal color. Taking into account the luminance efficacy of radiation (LER) and feasible laser wavelengths in practice, we get a practical design of wavelengths and power for a laser projection display with 6 primaries, which covers 96.6% of the optimal color gamut.

Spectral locus interpolation with splines in optical instruments

The article deals with the problem of representation of the spectral locus curve on the CIE xy chromaticity diagram. The issue is that spectral locus is specified at discrete set of points corresponding to given set of wavelengths of monochromatic colors. Thus, the problem appears which way to calculate chromaticity coordinates for any other wavelength. Three different methods how to interpolate the spectral locus were considered. The method we proposed to build an interpolant curve is based on using of Bezier curves. This approach allows to calculate chromaticity coordinates for any arbitrary wavelength directly on the CIE xy chromaticity diagram. Obtained analytical expressions for the spectral locus curve will increase the evaluation accuracy of the luminous radiation dominant wavelength value which defines the hue and the saturation value of the emitting color and other things.

Correspondence analysis of color–emotion associations

AbstractEmotions are often associated with colors, but what mediates color–emotion associations is not fully understood. This study examined associations between colors and emotions using correspondence analysis. The hypothesis that emotions are associated with colors through the correspondence between the hue circle and the circumplex model of emotion/affect was tested. Participants viewed 40 colors and reported a word that expressed an emotion that they associated with or felt in response to each color. Participants' responses were aggregated into a contingency table of colors and emotion words, and a correspondence analysis was conducted. An eight‐dimensional biplot was obtained. The first and second dimensions were related to hue, and the hue configuration was similar to colors' spectral trajectory in the CIE xy space or the CIELAB a*b* color space. The configuration of emotions was not consistent with the circumplex model of emotion, which rejected the above hypothesis. The associations in dimensions 1 and 2 appeared to be mediated by the perceived temperature of colors and emotions. In dimensions 3–6, dimensions that seemed to reflect secondary associations based on cultural convention or personal experiences (such as white with emotionless and purity and blue with depression) were obtained. These results also demonstrated the usefulness of correspondence analysis for analyzing color–emotion associations due to its ability to reveal the underlying statistical structure of associations.

Blue Light Emitting Polyphenylene Dendrimers with Bipolar Charge Transport Moieties

Two light-emitting polyphenylene dendrimers with both hole and electron transporting moieties were synthesized and characterized. Both molecules exhibited pure blue emission solely from the pyrene core and efficient surface-to-core energy transfers when characterized in a nonpolar environment. In particular, the carbazole- and oxadiazole-functionalized dendrimer (D1) manifested a pure blue emission from the pyrene core without showing intramolecular charge transfer (ICT) in environments with increasing polarity. On the other hand, the triphenylamine- and oxadiazole-functionalized one (D2) displayed notable ICT with dual emission from both the core and an ICT state in highly polar solvents. D1, in a three-layer organic light emitting diode (OLED) by solution processing gave a pure blue emission with Commission Internationale de l’Éclairage 1931 CIE xy = (0.16, 0.12), a peak current efficiency of 0.21 cd/A and a peak luminance of 2700 cd/m2. This represents the first reported pure blue dendrimer emitter with bipolar charge transport and surface-to-core energy transfer in OLEDs.

An experimental study of yellow shift in injection-molded light guide plate

Recently, the size of light guide plate (LGP) in LCD-BLU (Backlight Unit) module is getting thinner and larger than ever. The part reached critical thickness to mold it by conventional injection molding methods due to the low flowability, melt solidification, machine limitation, and so on. Therefore, severe conditions have been applied to the part to increase the flowability such as high injection speeds and higher melt temperature. However, these approaches lead to the degradation of material and loss of optical properties. These defects are connected to the invisible part failure, so called, yellowing and color shift. In the present study a series of injection molding experiments were conducted to understand the distribution of yellowness in injection-molded LGP, and how the optical properties change under various injection molding conditions. Optical properties of yellow index (YI), CIE xy, and spectral transmittances of LGP sample were analyzed by the UV-visible spectrophotometer. Also, correlations between optical properties and process conditions were investigated from the Design of experiment (DOE). Interestingly, the value of YI, i.e., yellow shift in CIE diagram showed the maximum near the gate and decreased as the distance from the gate increased. Furthermore, as far as yellow shift concerned the data of direct transmittance are much more useful than total transmittance for evaluating color behavior. Meanwhile, analysis of variance (ANOVA) was conducted to see the effectiveness of chosen processing parameters. Mold temperature was found to be the most influential factor on the color shift and injection speed, melt temperature, packing pressure were followed.

Minimal-Energy Control Sequences for Linear Multi-Primary Displays

A control sequence gives the intensities of the primaries for a pixel in a display. A multi-primary display has four or more primaries, so that multiple control sequences can sometimes produce the same color. Different primaries likely consume different amounts of energy; furthermore, the energy consumption can be a complicated function. A minimal-energy control sequence for a target color produces that color with as little energy as possible. This article shows that such minimal-energy sequences take a simple geometric form when each primary’s energy function is linear. The display gamut, in CIE XY Z space, can be dissected into parallelepipeds. The originating vertex of each parallelepiped is the sum of a set of primaries at full intensity. Each edge of a parallelepiped is the translation of one primary. A color with XYZ coordinates in a certain parallelepiped is a unique linear combination of the primaries in the originating vertex, and the three edge primaries. This article proves that there exists a dissection such that these linear combinations are minimal-energy control sequences. In the generic case, this dissection is unique. An algorithm for a minimal-energy dissection is presented, along with an example.

Color-discrimination threshold determination using pseudoisochromatic test plates.

We produced a set of pseudoisochromatic plates for determining individual color-difference thresholds to assess test performance and test properties, and analyzed the results. We report a high test validity and classification ability for the deficiency type and severity level [comparable to that of the fourth edition of the Hardy–Rand–Rittler (HRR) test]. We discuss changes of the acceptable chromatic shifts from the protan and deutan confusion lines along the CIE xy diagram, and the high correlation of individual color-difference thresholds and the red–green discrimination index. Color vision was tested using an Oculus HMC anomaloscope, a Farnsworth D15, and an HRR test on 273 schoolchildren, and 57 other subjects with previously diagnosed red–green color-vision deficiency.

Core-and-surface-functionalized polyphenylene dendrimers for solution-processed, pure-blue light-emitting diodes through surface-to-core energy transfer.

Several pyrene-based polyphenylene dendrimers (PYPPDs) with different peripheral chromophores (PCs) are synthesized and characterized. Deep blue emissions solely from the core are observed for all of them in photoluminescence spectra due to good steric shielding of the core and highly efficient surface-to-core Förster resonant energy transfers (FRETs). Device performances are found in good correlation with the energy gaps between the work function of the electrodes and the frontier molecular orbital (FMO) levels of the PCs. Pure blue emission, luminance as high as 3700 cd m(-2) with Commission Internationale de l'Éclairage 1931 (CIE(xy)) = (0.16, 0.21), and a peak current efficiency of 0.52 cd A(-1) at CIE(xy) = (0.17, 0.20) are achieved. These dendrimers are among the best dendritic systems so far for fluorescent blue light-emitting materials.

Bright Blue and White Electrophosphorescent Triarylboryl‐Functionalized C^N‐Chelate Pt(II) Compounds: Impact of Intramolecular Hydrogen Bonds and Ancillary Ligands

New blue and blue‐green phosphorescent C^N chelate Pt(II) compounds that contain a dimesitylboryl‐functionalized phenyl‐1,2,3‐triazole ligand (Bptrz) are synthesized. The influence of three different ancillary ligands, namely acetylacetonato (acac), picolinate (pic) and pyridyl‐1,2,4‐triazolyl (pytrz), on phosphorescence quantum efficiency and excimer emission is examined. Pt(II) compounds with a p‐Bptrz ligand consistently emit a blue‐green color with an emission wavelength = 490–500 nm while those with a m‐Bptrz ligand emit a blue color with λem = 450–460 nm and a quantum efficiency as high as 0.97. In addition to the blue monomer emission peak, Pt(m‐Bptrz)(pytrz) compounds display an excimer emission peak at ∼550 nm in a solid matrix whose intensity is dependent on the substituent group on pytrz and the doping concentration. As a result of the monomer and excimer emission, bright white phosphorescence is observed for several members of Pt(m‐Bptrz)(pytrz) compounds. Intramolecular CH···N hydrogen bonds are found to play an important role in the high stability and high phosphorescent quantum efficiency of Pt(m‐Bptrz)(pytrz) compounds. Single‐dopant blue and white electrophosphorescent devices using Pt(m‐Bptrz)(CF3‐pytrz‐Me) or Pt(m‐Bptrz)(t‐Bu‐pytrz‐Me) as the emitter are successfully fabricated. White electroluminesence devices with external quantum efficiency of 15.6% and CIE (xy) of 0.31, 0.44 are achieved.

Categorical properties of the color term "GOLD"

Humans are able to categorize an infinite variety of surface colors into a small number of color terms. Previous studies have shown that 11 basic color terms are commonly used in fully developed languages. These studies usually used flat matte color plates as stimuli, but we can also perceive the colors of glossy surfaces by discounting the effect of the gloss. However, color terms such as GOLD and SILVER are specifically associated with glossy surfaces. In this study, we conducted a categorical color-naming task to examine whether the color terms GOLD and SILVER could be located in a stimulus space defined by combining CIE xy chromaticity coordinates and surface reflectance and whether they had categorical properties like ordinary basic color terms. We found that GOLD and SILVER were used for specific ranges of chromaticities with stimuli having large specular reflectances. Moreover, the strengths of the categorical properties, as assessed using measures of consistency, consensus, and reaction time, were comparable to those of the basic color terms, indicating that GOLD and SILVER are categorical color terms specifically associated with glossy surfaces. This also indicates that humans do not always discount surface gloss to identify colors but can utilize this information to categorize colors.

A Study on White Organic Light-Emitting Diodes Co-Doped with Red Fluorescent and Blue Phosphorescent Dopants

White organic light-emitting diodes (WOLEDs) have drawn increasing attention due to their potential use in various applications such as solid-state lighting and backlight of liquid crystal displays and full-color OLEDs of red, green, and blue pixel. N,N'-dicabazolyl-3,5-benzene (mCP), the host material, was co-doped with Iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2']-picolinate (FIrpic), which functions not only as phosphorescent sensitizer but also blue emitter, and (2Z,2'Z)-3,3'-[4,4"-bis (dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]bis (2-phenylacrylonitrile) (ABCV-P), which is a red fluorescent material. The fabricated device structures were as follows: (device A) Indium tin oxide (ITO)/N,N'-bis-(1-naphyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine (NPB)/(mCP)/mCP:ABCV-P (1%)/4,7-diphenyl-1,10-phenanthroline (Bphen)/lithium quinolate (Liq)/aluminum (Al), (device B) ITO/NPB/mCP/mCP:FIrpic (8%)/Bphen/Liq/Al and (device C) ITO/NPB/mCP/mCP:FIrpic:ABCV-P (8%, 1%)/Bphen/Liq/Al, respectively. Phosphorescent FIrpic harvesting both singlet and triplet excitions not only emitted blue light but also transferred energy to fluorescent ABCV-P. The maximum luminance efficiency, external quantum efficiency, and luminance of white light device were measured to be 5.95 cd/A, 2.45% and 2500 cd/m2, respectively. The white device gave practically white light with the Commision Internationale de l'Eclairage (CIE(xy)) coordinate of (0.44, 0.49) which was close to warm white color (CIE(xy) = 0.45, 0.45).

Detection and correction of purple fringing using color desaturation in the xy chromaticity diagram and the gradient information

This paper proposes a method to detect and correct purple fringing, which is one of color artifacts due to characteristics of charge coupled device sensors in a digital camera. The proposed method consists of two steps: detection and correction of purple fringing. In the first step, we detect the purple fringed regions that satisfy specific properties: image regions with large gradient magnitudes and with the chromaticity values within the purple color range set in the CIE xy chromaticity diagram. In the second step, color of the purple fringed regions is corrected in the CIE xy chromaticity diagram by color desaturation of the detected pixels. The proposed method is able to detect purple fringe artifacts more precisely and correct them more naturally than existing methods. It can be used as a post processing in a digital camera.

Syntheses, Photophysics, and Application of Iridium(III) Phosphorescent Emitters for Highly Efficient, Long‐Life Organic Light‐Emitting Diodes

Rational design and synthesis of Ir(III) complexes (1-3) bearing two cyclometalated ligands (C--N) and one 2-(diphenylphosphino)phenolate chelate (P--O) as well as the corresponding Ir(III) derivatives (4-6) with only one (C--N) ligand and two P--O chelates are reported, where (C--NH)=phenylpyridine (ppyH), 1-phenylisoquinoline (piqH), and 4-phenylquinazoline (nazoH). Single crystal X-ray diffraction studies of 3 reveal a distorted octahedral coordination geometry, in which two nazo ligands adopt an eclipsed configuration, with the third P--O ligand located trans to the phenyl group of both nazo ligands, confirming the general skeletal pattern for 1-3. In sharp contrast, complex 4 reveals a trans-disposition for the PPh2 groups, along with the phenolate groups residing opposite the unique cyclometalated ppy ligand, which is the representative structure for 4-6. These Ir(III) complexes exhibit green-to-red photoluminescence with moderate to high quantum efficiencies in the degassed fluid state and bright emission in the solid state. For 1-6, the resolved emission spectroscopy and relaxation dynamics are well rationalized by the computational approach. OLEDs fabricated using 12 wt. % of 3 doped in CBP and with BCP as hole blocking material, give bright electroluminescence with lambda(max)=628 nm and CIE(xy) coordinates (0.65, 0.34). The turn-on voltage is 3.2 V, while the current efficiency and the power efficiency reach 11.2 cd A(-1) and 4.5 lm W(-1) at 20 mA cm(-2). The maximum efficiency reaches 14.7 cd A(-1)and 6.8 lm W(-1) upon switching to TPBI as hole blocking material. For evaluating device lifespan, the tested device incorporating CuPc as a passivation layer, 3 doped in CTP as an emitting layer, and BAlq as hole blocking material, shows a remarkably long lifetime up to 36,000 h at an initial luminance of 500 cd m(-2).

A Red Doped OLEDS with a Good Device Performance at High Doping Concentration

A new red fluorescent material, (2E,2′E)-3,3′-[4,4″-bis(dimethylamino)-1,1′:4′, 1″-terphenyl-2′,5′-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th), for organic light emitting diodes (OLEDs) was synthesized and characterized. Photoluminescence spectrum of ABCV-Th in chloroform solution was peaked at 618 nm. The red doped OLEDs with the structure of ITO/NPB/MADN: ABCV-Th (x%)/BCP/Alq3/Liq/Al were fabricated to investigate the influence of doping concentration on the device performance. The ABCV-Th doped device with doping concentration of 15% showed the Commission Internationale d'Eclairage (CIE xy ) coordinate of (0.58, 0.42) at the maximum luminance of 7320 cd/m2 and this is comparable to that of the traditional 4-(dicyanomethylene)-2-methyl-6-(julolidin-4-yl-vinyl)-4H-pyran (DCM2) doped OLED (CIE xy = 0.58, 0.41, 1032 cd/m2 at 18 V).

A Non-Doped Organic Light Emitting Diode with Pure Red Emission Using a New Host Emitter

A red fluorescent material (2E,2'E)-3,3'-[4,4"-bis(dimethylamino)-1,1': 4',1 "-terphenyl-2',5'-diyl]bis[2-(2-thienyl)acrylonitrile] (ABCV-Th) was synthesized for use in organic light emitting diodes (OLEDs) as the host emissive material. It has been reported some green and blue host emissive materials used in OLEDs revealed high device performance but, owing to concentration quenching, comparable red light emitting materials are still rare in OLEDs application. Non-doped organic light emitting diodes, with the structure of ITO/NPB/ABCV-Th (30 nm and 50 nm)/BCP/Alq3/Liq/Al were fabricated using ABCV-Th as the host emitter. The peak wavelength and full width at half maximum (FWHM) of electroluminescence (EL) were 629.5 nm and 68.5 nm, respectively. The maximum brightness and turn on voltage of the device were measured to be 1330 cd/m2 at 14.6 V and 3.4 V, respectively. The device exhibited authentic red emission (Commission Internationale De L'Eclairage (CIE(xy)) = 0.65, 0.34) which is almost close to the standard red (CIE(xy) = 0.67, 0.33) demanded by the national television system committee (NTSC).

Representations of Relative Display Gamut Size

Gamut size of a wide gamut display is usually represented with the ratio of its chromaticity triangle area and the chromaticity triangle area of a standard display in CIE xy color coordinates. Such a chromaticity area ratio (CAR) is a rough relative gamut size, because CIE xy is a nonuniform color coordinate system and display gamut is a volume in color space. The representation of relative gamut size with the ratio of the discernible color numbers in a display gamut and NTSC TV gamut is studied. This ratio is called the discernible color number ratio (DCNR). Discernible color number is counted with CIE94 color difference formula in CIELAB color space. It is found that CAR is larger than DCNR for the display with primary purity higher than NTSC primary purity. For example, the CAR of a practical light-emitting diode (LED) display with respect to NTSC TV is 7.8% overestimated, in which red, green, and blue LED primary wavelengths are 625, 520, and 470 nm, respectively; red, green, and blue LED bandwidths are 20, 40, and 30 nm, respectively. In addition, the DCNRs of wide gamut displays with respect to the object color of the same white illuminant are investigated. It is shown that the gamut size improvement for laser display compared with LED display is not significant.

Determination of Gamut Boundary Description for multi-primary color displays

Displays with a larger color gamut to represent the images of the small color gamut are emphasized in the display development trend recently. Resulting from the vigorous development of Light Emitting Diodes (LEDs), the solutions to enlarge the color gamut which is formed a polygon area by adding multiple primary colors are possible, easier and inexpensive considerably. Therefore, how to determine the Gamut Boundary Description (GBD) plays a significant role for the applications of the multiple primary color displays, where the primaries form a convex polygon in CIE xy space. The paper proposed a method to construct the three-dimension color volume of GBD from the two-dimension polygon gamut area precisely regardless of that how many multiple primary colors the displays have. The method is examined in detail by the simulations and experiments, and proved it to fulfill from tri-primary color device to Nprimary color device.