Color-rendering Properties Research Articles

A new paradigm for smart packaging: A dual-channel freshness monitoring platform based on aerogels of sodium alginate-anthocyanin complex with high colorimetric sensitivity and stability

Global seafood consumption is estimated at 156 million tons annually, with an economic loss of >25 billion euros annually due to marine fish spoilage. In contrast to traditional smart packaging which can only roughly estimate food freshness, an intelligent platform integrating machine learning and smart aerogel can accurately predict remaining shelf life in food products, reducing economic losses and food waste. In this study, we prepared aerogels based on anthocyanin complexes that exhibited excellent environmental responsiveness, high porosity, high color-rendering properties, high biocompatibility, high stability, and irreversibility. The aerogel showed excellent indication properties for rainbow trout and proved suitable for fish storage environments. Among the four machine learning models, the radial basis function neural network and backpropagation network optimized by genetic algorithm demonstrated excellent monitoring performance. Also, the two-channel dataset provided more comprehensive information and superior descriptive capability. The three-layer structure of the monitoring platform provided a new paradigm for intelligent and sophisticated food packaging. The results of the study might be of great significance to the food industry and sustainable development.

Color Rendering Index over 95 Achieved by Using Light Recycling Process Based on Hybrid Remote-Type Red Quantum-Dot Components Applied to Conventional LED Lighting Devices.

Red color conversion materials have often been used in conventional white LEDs (light-emitting diodes) to enhance the insufficient deep-red component and thus improve the color-rendering property. Quantum dots (QDs) are one of the candidates for this due to their flexibility in controlling the emission wavelength, which is attributed to the quantum confinement effect. Two types of remote QD components, i.e., QD films and QD caps, were prepared and applied to conventional white LED illumination to improve the color-rendering properties. Thanks to the red component near 630 nm caused by the QD components, the color rendering indices (CRIs) of both Ra and R9 could be increased to over 95. It was found that both the diffusing nature of the reflector and the light recycling process in the vertical cavity between the bottom reflector and the top optical films play important roles in improving the color conversion efficiency of remote QD components. The present study showed that the proper application of remote QDs combined with a suitable optical cavity can control the correlated color temperature of the illumination over a wide range, thus realizing different color appearances of white LED illumination. In addition, a high CRI of over 95 could be achieved due to the sufficient excitation from fewer QDs, due to the strong optical cavity effect.

Long-Term Performance of Monolithic Silica Aerogel with Different Hydrophobicities: Physical and Color Rendering Properties after an Accelerated Aging Process.

Due to its excellent properties, monolithic silica aerogel is a promising material for innovative glazing systems. Since glazing systems are exposed to deteriorating agents during building service life, it is essential to investigate the long-term performance of aerogel. In the present paper, several 12.7 mm-thick silica aerogel monoliths produced by a rapid supercritical extraction method were tested, including both hydrophilic and hydrophobic samples. After fabrication and characterization of hydrophobicity, porosity, optical and acoustic properties, and color rendering, the samples were artificially aged by combining temperature and solar radiation effects in an experimental device specifically developed at the University of Perugia. The length of the experimental campaign was determined using acceleration factors (AFs). Temperature AF was evaluated according to the Arrhenius law using thermogravimetric analysis to estimate the aerogel activation energy. A natural service life of 12 years was achieved in about 4 months, and the samples' properties were retested. Contact angle tests supported by FT-IR analysis showed loss of hydrophobicity after aging. Visible transmittance values in the 0.67-0.37 range were obtained for hydrophilic and hydrophobic samples, respectively. The aging process involved optical parameter reduction of only 0.02-0.05. There was also a slight loss in acoustic performance (noise reduction coefficient (NRC) = 0.21-0.25 before aging and NRC = 0.18-0.22 after aging). For hydrophobic panes, color shift values in the 10.2-59.1 and 8.4-60.7 ranges were obtained before and after aging, respectively. The presence of aerogel, regardless of hydrophobicity, results in a deterioration in light-green and azure tones. Hydrophobic samples had lower color rendering performance than hydrophilic aerogel, but this did not worsen after the aging process. This paper makes a significant contribution to the progressive deterioration assessment of aerogel monoliths for applications in sustainable buildings.

Structural Optimization of Vertically-Stacked White LEDs with a Yellow Phosphor Plate and a Red Quantum-Dot Film.

A remote-type white light-emitting diode (LED) consisting of a red quantum-dot (QD) film and a yellow phosphor plate was studied by both experiment and optical simulation. The sequence of the two color-conversion films had a substantial effect on the color-rendering properties of the vertically-stacked white LED, and the optimized configuration exhibited a high color rendering index of more than 90 thanks to the enhanced red component via the QD film. For the design of high-power white LED devices of a remote type, it was necessary to locate the color-conversion films below the diffuser plate to remove the substantial color dispersion depending on the viewing angle. The present study shows that high power and high color-rendering white LED devices can be realized in terms of two vertically-stacked color-conversion materials, which would provide long-term stability due to the remote design.

Substantial Improvement of Color-Rendering Properties of Conventional White LEDs Using Remote-Type Red Quantum-Dot Caps.

A new type of remote red quantum-dot (QD) component was designed and fabricated to improve the color-rendering properties of conventional white LED (light-emitting diode) lightings. Based on an optical simulation, the rectangular cavity-type QD cap was designed with an opening window on the top surface. Red QD caps were fabricated using a typical injection molding technique and CdSe/ZnS QDs with a core/shell structure whose average size was ~6 nm. Red QD caps were applied to conventional 6-inch, 15-W white LED downlighting consisting of 72 LEDs arrayed concentrically. The red QD caps placed over white LEDs enhanced the red components in the long-wavelength range resulting in the increase of the color rendering index (CRI) from 82.9 to 94.5. The correlated color temperature was tuned easily in a wide range by adopting various configurations consisting of different QD caps. The spatial and angular homogeneities were secured on the emitting area because QD caps placed over the white LEDs did not exhibit any substantial optical path length difference. The present study demonstrates that adopting QD caps in conventional LED lightings provides a flexible and efficient method to realize a high color-rendering property and to adjust correlated color temperature appropriately for a specific application.

Insight into the Effect of Counterions on the Chromatic Properties of Cr-Doped Rutile TiO2-Based Pigments.

Rutile TiO2 pigments codoped with chromophore ion Cr3+ and various charge-balancing ions (i.e., counterions species of Sb, Nb, W and Mo) were prepared by a solid-phase reaction method. The effects of the counterions and calcination temperatures on the phase structure, color-rendering and spectroscopic properties, microstructure, and stability of the synthesized pigments were investigated in detail. The results showed that the introduction of 5–10% counterions improved the solubility of Cr3+ in the TiO2 lattice to form the single-phase rutile pigments calcined at 1100 °C for 2 h. The 10% Cr-doped pigment showed a dark brown color. Depending on the content and type of counterions, the color of the codoped pigments was tailored from yellow to reddish or yellowish-orange to black with different brightness and hue. The influence mechanism of counterions was ascribed to the lattice distortion and variation in the charge balance condition. It was found that the addition of Sb, Nb, or Mo resulted in a remarkable improvement in the NIR reflectance of pigments. The grain growth was inhibited with the codoping of Cr/Sb and Cr/Nb to achieve the nano-sized pigments. In addition, the prepared pigments exhibited good acid and alkali corrosion resistance as well as excellent stability and coloring performance in transparent ceramic glazes.

A Study on Simultaneous Improvement of S/P Ratio and Color Rendering Properties of CCT-tunable Phosphor-Converted LED Lighting Located on the Planckian Locus

A Study on Simultaneous Improvement of S/P Ratio and Color Rendering Properties of CCT-tunable Phosphor-Converted LED Lighting Located on the Planckian Locus

Improvement of color-rendering characteristics of white light emitting diodes by using red quantum dot films

Red quantum dot (QD) films were applied to a conventional white light-emitting-diodes (LEDs) module consisting of 72 LEDs for improving color-rendering properties. Total three QD films with different QD concentrations, two diffuser plates, and six optical configurations were combined and investigated to find an optimized optical structure. QD films formed a red peak near 630 nm in the spectrum which significantly increased the overall color rendering index (CRI). The lateral optical cavity formed by a vertical QD wall and the vertical cavity formed by the diffuser plate and the reflection film in the lighting module played an important role in the improvement of the color-rendering properties. Especially, the adoption of the lateral optical cavity formed by the QD wall was an effective way to improve both efficiency and color rendering properties of the LED lighting. The present result suggests a new possibility of designing high-CRI LED light sources whose color properties can be tuned easily by simply applying and relocating QD components in conventional LED lightings.

MPD growth of single crystals of Ce3+ doped Gd3−xLuxAl5−yGayO12 mixed garnets and their luminescent, scintillation and photoconversion properties

This work deals with the growth of Ce3+ doped Gd3−xLuxAl5−yGayO12 mixed single crystals garnets by the micro-pulling down method and their development as phosphor-convertors of white LED (pc-WLED) and scintillators. In this research, the influence of combined technique of the “band-gap engineering” and “positioning of Ce3+ 5d-levels” in Gd3−xLux Al5−yGayO12 single crystals at x = 0 – 1.5 and y = 2–2.5 ranges, is studied with the aim to improve the material properties such as color-rendering properties of pc-WLEDs, as well as scintillation. The luminescent, scintillation and photoconversion properties of Gd3−xLuxAl5−yGayO12:Ce crystals were investigated as a function of the Gd/Lu ratio. We reviled that Gd3−xLuxAl3−2.5Ga2−2.5O12:Ce crystals at × = 1–1.5 show the best photoconversion and scintillation properties.

Green and high yield synthesis of CdTe@Hydrotalcite nanocrystals with enhanced photoluminescence stability toward white light emitting diodes

As a new type of luminescent material, quantum dots (QDs) with adjustable photoluminescence and narrow emission have attracted extensive attention in various fields. However, the large-scale production of QDs powders with high stability remains a key challenge, which greatly limits their wide applications. In this work, we synthesized highly stable QDs powders via a facile and simple co-precipitation method by embedding CdTe QDs into inorganic Mg2Al(OH)7 hydrotalcite matrix. This method shows distinct advantages of rapid separation of QDs powder through simple filtration, leading to a high yield of QDs powders and effectively avoiding heavy metal ions waste water. Compared with the parental CdTe QDs, the as-prepared CdTe@Mg2Al(OH)7 composites exhibit enhanced photoluminescence stability, longer photoluminescence decay lifetime, and better thermostability due to the protection of the Mg2Al(OH)7 hydrotalcite matrix. Based on the above excellent properties, we utilized the CdTe@Mg2Al(OH)7 powders as a red light conversion layer to prepare white light emitting diodes, which show high color-rendering properties with Commission Internationale de L'Eclairage (CIE) color coordinate of (0.3639, 0.3531), high color rendering index (CRI) value of 88, and color temperature (Tc) of 5112 K at 20 mA. This work offers an environmental friendly, low-cost and large-scale production route for high-performance QDs powders.

Visual Appearance of Nanocrystal-Based Luminescent Solar Concentrators.

The luminescent solar concentrator (LSC) is a promising concept for the integration of photovoltaic (PV) generators into the building envelope. Having the form of semitransparent plates, LSCs offer a high degree of flexibility and can be used as windows or facades, as part of the of building-integrated photovoltaic (BIPV) industry. Existing performance characterizations of LSC devices focus almost exclusively on electric power generation. However, when used as window components, the transmitted spectrum can alter the color, potentially affecting the visual comfort of the occupants by altering the properties of the sunlight. In this study, eight different state-of-the-art nanocrystals are evaluated as potential candidates for LSC window luminophores, using Monte Carlo simulations. The transparency of each LSC window varies between 90% and 50%, and the color-rendering properties are assessed with respect to the color rendering index (CRI) and the correlated color temperature (CCT). It is found that luminophores with a wide absorption bandwidth in the visible spectrum can maintain a high CRI value (above 85) and CCT values close to the Planckian locus, even for high luminophore concentrations. In contrast, luminophores that only absorb partly in the visible spectrum suffer from color distortion, a situation characterized by low CCT and CRI values, even at high transmittance.

The characterization of Ce/Pr-doped YAG phosphor ceramic for the white LEDs

Ce/Pr -doped YAG (Ce:Pr:YAG) transparent ceramics are fabricated by the vacuum sintering. The crystal structure and morphology, the energy transfer between Ce3+ and Pr3+, and luminescence properties are measured and discussed. The effect of the micrographs of the starting powders and the doping contents of Ce3+ and Pr3+ ions on the microstructure of YAG ceramic is also exhibited. In the photoluminescence spectra, the characteristic emission peaks of Pr3+ ions at 608 nm and 638 nm are observed, and therefore white light-emitting diodes (WLEDs) with improved color-rendering properties obtained by using modified Ce:Pr:YAG phosphors. The composite phase structure of ceramic phosphor is designed for improving the extraction efficacy and increasing the luminous efficacy by breaking the total internal reflection (TIR) at the interface between air and ceramic.

Real-Time Closed-Loop Color Control of a Multi-Channel Luminaire Using Sensors Onboard a Mobile Device

Smart homes and Internet of Things are emerging concepts in modern society, with intelligent lighting being an important part of it. Besides providing visual satisfaction through its color-rendering properties, lighting also has other effects on human well-being. In order to exploit the full potential of a smartly lit home, lighting systems need to be equipped with accurate controllers that can control the spectrum and color characteristics of light in addition to conventional ON–OFF and dimming control. However, current commercial smart lighting products with such capabilities need to employ expensive sensors which are still lacking in terms of closed-loop feedback which is imperative for accurate color control of light-emitting diode (LED)-based luminaires. This paper presents a novel approach that uses the camera available on modern smartphones to perform closed-loop color control for lighting systems in smart homes. The algorithm is able to perform multi-channel mixing for any color and also white light at a desired correlated color temperature with high color-rendering index. This approach proves to be very economical and convenient as no external sensors are required and can be performed using any Android smartphone on a compatible LED-based luminaire.

Appropriate indices for color rendition and their recommended values for UHDTV production using white LED lighting.

We selected appropriate indices for color rendition and determined their recommended values for ultra-high-definition television (UHDTV) production using white LED lighting. Since the spectral sensitivities of UHDTV cameras can be designed to approximate the ideal spectral sensitivities of UHDTV colorimetry, they have more accurate color reproduction than HDTV cameras, and thus the color-rendering properties of the lighting are critical. Comparing images taken under white LEDs with conventional color rendering indices (Ra, R9-14) and recently proposed methods for evaluating color rendition of CQS, TM-30, Qa, and SSI, we found the combination of Ra and R9 appropriate. For white LED lighting, Ra ≥ 90 and R9 ≥ 80 are recommended for UHDTV production.

Relationship between Color Rendering Properties of Pseudo-white LED and Object’s Surface Colors

Relationship between Color Rendering Properties of Pseudo-white LED and Object’s Surface Colors

Quantum Dots-Converted Light-Emitting Diodes Packaging for Lighting and Display: Status and Perspectives

Recent years, semiconductor quantum dots (QDs) have attracted tremendous attentions for their unique characteristics for solid-state lighting (SSL) and thin-film display applications. The pure and tunable spectra of QDs make it possible to simultaneously achieve excellent color-rendering properties and high luminous efficiency (LE) when combining colloidal QDs with light-emitting diodes (LEDs). Due to its solution-based synthetic route, QDs are impractical for fabrication of LED. QDs have to be incorporated into polymer matrix, and the mixture is dispensed into the LED mold or placed onto the LED to fabricate the QD–LEDs, which is known as the packaging process. In this process, the compatibility of QDs' surface ligands with the polymer matrix should be ensured, otherwise the poor compatibility can lead to agglomeration or surface damage of QDs. Besides, combination of QDs–polymer with LED chip is a key step that converts part of blue light into other wavelengths (WLs) of light, so as to generate white light in the end. Since QD-LEDs consist of three or more kinds of QDs, the spectra distribution should be optimized to achieve a high color-rendering ability. This requires both theoretical spectra optimization and experimental validation. In addition, to prolong the reliability and lifetime of QD-LEDs, QDs have to be protected from oxygen and moisture penetration. And the heat generation inside the package should be well controlled because high temperature results in QDs' thermal quenching, consequently deteriorates QD-LEDs' performance greatly. Overall, QD-LEDs' packaging and applications present the above-mentioned technical challenges. A profound and comprehensive understanding of these problems enables the advancements of QD-LEDs' packaging processes and designs. In this review, we summarized the recent progress in the packaging of QD-LEDs. The wide applications of QD-LEDs in lighting and display were overviewed, followed by the challenges and the corresponding progresses for the QD-LEDs' packaging. This is a domain in which significant progress has been achieved in the last decade, and reporting on these advances will facilitate state-of-the-art QD-LEDs' packaging and application technologies.

An Overview of the Impact of Dimming Metal Halide Discharge Lamps

A summary of the changes induced by operating metal halide discharge lamps below their rated power is presented. The changes for lamps, which operate under saturated dose conditions, are lowering of luminous efficacy, an increase in correlated color temperature, and a reduction in color-rendering properties. The impacts of these changes are reviewed with respect to the visual appearance of lighting installations, the reliability of lamps when operated for prolonged periods at reduced power, and some commercial consequences. The changes in output characteristics are much less marked if the lamp operates in an unsaturated dose regime.

Accurate control of chromaticity and spectra by feedback phosphor-coating.

The chromaticity coordinates and spectra of phosphor-converted LEDs are demonstrated to be well controlled in this study. Through the feedback coating method of stacked yellow, green, and red phosphor layers, the color rendering index (CRI), correlated color temperature (CCT), and spectra are determined to match precisely the desired target. In addition, the reabsorption effect is strongly influenced by the order of stacked phosphor layers and the selected excitation wavelength of phosphors. The degree of reabsorption will modify the original spectra and cause a mismatch between the experimental measurement and the simulation based on the linear superposition of blue light and phosphor-emitted light. This feedback coating method offers an easy approach towards optimized spectra, which can offer the highest luminous efficacy of radiation with excellent color-rendering properties.

Hybrid 2D photonic crystal-assisted Lu3Al5O12:Ce ceramic-plate phosphor and free-standing red film phosphor for white LEDs with high color-rendering index.

This paper reports the combined optical effects of a two-dimensional (2D) SiNx photonic crystal layer (PCL)-assisted Lu3Al5O12:Ce (LuAG:Ce) green ceramic-plate phosphor (CPP) and a free-standing (Sr,Ca)AlSiN3:Eu red film phosphor to enhance luminous efficacy, color rendering index (CRI), and special CRI (R9) of LuAG:Ce CPP-capped white light-emitting diodes (LEDs) for high-power white LEDs at 350 mA. By introducing the 2D SiNx PCL, the luminous efficacy was improved by a factor of 1.25 and 1.15 compared to that of the conventional flat CPP-capped LED and the thickness-increased CPP-capped LED (with a thickness of 0.15 mm), respectively, while maintaining low color-rendering properties. The combining of the free-standing red film phosphor in the flat CPP-capped, the 2D PCL-assisted CPP-capped, and the thickness-increased CPP-capped LEDs led to enhancement of the CRI and the special CRI (R9); it also led to a decrease of the correlated color temperature (CCT) due to broad wavelength coverage via the addition of red emission. High CRI (94), natural white CCT (4450 K), and acceptable luminous efficacy (71.1 lm/W) were attained from the 2D PCL-assisted LuAG:Ce CPP/free-standing red film phosphor-based LED using a red phosphor concentration of 7.5 wt %. It is expected that the combination of the 2D PCL and the free-standing red film phosphor will be a good candidate for achieving a high-power white CPP-capped LED with excellent CRI.

基于反应时间的中间视觉道路照明功率密度分析及显色性能研究

A research method of analysis of the road lighting source safety and energy-saving properties under the human mesopic conditions was given. By constructing the reaction time test system for road lighting under the mesopic vision,the luminous efficiency model was established and luminous efficiency curve was obtained. By using this model,the evaluation method of energy efficiency based on the lighting power density was given. Using the calculation and analysis method of the color-rendering properties based on the color-rendering index,the effect of the changes in relative spectral power distribution on the color of light source was discussed under Luv uniform color space,and the function expression between the dominant wavelength of the light source and color-rendering index was established,which can be used to obtain the relationship between human sensitivity and light source color of each wavelength point. The above method was verified by the reaction time simulation test and the definition of the road lighting picture calculation experiment. The results show that the green-white light source with dominant wavelength of 540- 550 nm has the best power-saving and color-rendering properties under the mesopic vision.