Color-rendering Properties Research Articles

System efficiency of laser-based white light

Abstract For many lighting applications, light-emitting diodes (LEDs) are replacing traditional light sources providing the possibility for smart and efficient systems as well as a reduction in the product weight. A next step in this development is the integration of laser-based light sources to increase luminance and to further scale down the optics possibly leading to a reduction of necessary resources. This article reviews the possibilities and challenges arising from the use of laser diodes especially compared to current high-power LED systems in terms of efficiency, color-rendering properties, and thermal management.

Assessing the colour quality of LED sources: Naturalness, attractiveness, colourfulness and colour difference

The CIE General Colour Rendering Index is currently the criterion used to describe and measure the colour-rendering properties of light sources. But over the past years, there has been increasing evidence of its limitations particularly its ability to predict the perceived colour quality of light sources and especially some LEDs. In this paper, several aspects of perceived colour quality are investigated using a side-by-side paired comparison method, and the following criteria: naturalness of fruits and vegetables, colourfulness of the Macbeth Color Checker chart, visual appreciation (attractiveness/ preference) and colour difference estimations for both visual scenes. Forty-five observers with normal colour vision evaluated nine light sources at 3000 K, and 36 observers evaluated eight light sources at 4000 K. Our results indicate that perceived colour differences are better dealt by the CIECAM02 Uniform Colour Space. Naturalness is better described by fidelity indices even if they did not give perfect predictions for all differences between LED light sources. Colourfulness is well described by gamut-based indices and attractiveness was found to correlate best with gamut-based indices but also with a preference index or a memory index calculated without blue and purple hues. A very low correlation was found between appreciation and naturalness indicating that colour quality needs more than one metric to describe subjective aspects.

High Color Rendering Properties of Full-color LED Light Equipment at AIST

High Color Rendering Properties of Full-color LED Light Equipment at AIST

Comparing colour discrimination and proofreading performance under compact fluorescent and halogen lamp lighting

Legislation in many countries has banned inefficient household lighting. Consequently, classic incandescent lamps have to be replaced by more efficient alternatives such as halogen and compact fluorescent lamps (CFL). Alternatives differ in their spectral power distributions, implying colour-rendering differences. Participants performed a colour discrimination task – the Farnsworth–Munsell 100 Hue Test – and a proofreading task under CFL or halogen lighting of comparable correlated colour temperatures at low (70 lx) or high (800 lx) illuminance. Illuminance positively affected colour discrimination and proofreading performance, whereas the light source was only relevant for colour discrimination. Discrimination was impaired with CFL lighting. There were no differences between light sources in terms of self-reported physical discomfort and mood state, but the majority of the participants correctly judged halogen lighting to be more appropriate for discriminating colours. The findings hint at the colour-rendering deficiencies associated with energy-efficient CFLs. Practitioner Summary: In order to compare performance under energy-efficient alternatives of classic incandescent lighting, colour discrimination and proofreading performance was compared under CFL and halogen lighting. Colour discrimination was impaired under CFLs, which hints at the practical drawbacks associated with the reduced colour-rendering properties of energy-efficient CFLs.

Museum Lighting and Color Rendering Properties of LED Light Sources(<Special Issue>Museum Lighting Renovation through LEDs)

Museum Lighting and Color Rendering Properties of LED Light Sources(<Special Issue>Museum Lighting Renovation through LEDs)

Preparation, characterization, and luminescence of Eu3+-doped gadolinium tungstate, Y3Al5O12:Ce phosphor, and their mixtures

A co-precipitation method was employed to prepare Eu3+-doped gadolinium tungstate and Y3Al5O12:Ce fluorescent powders. Eu3+-doped gadolinium tungstate phosphors can be effectively excited both by ultraviolet light at 395nm and blue light at 465nm and emit remarkably intense red emission at 613nm with near line spectrum. Ce3+-doped YAG can also efficiently absorb this blue light and produce a broad band of luminescence centering at 540nm. The red fluorescent powder and yellow fluorescent phosphor were then mixed together at different weight ratios. It is found that the emission spectra of the blended phosphors excited with blue light at 465nm is the superposition of the two phosphors, which means that the mixture’s emission can be tuned by controlling the weight ratios. These results demonstrated the possibility of using the blended phosphors to increase the color-rendering properties of white LEDs.

Influence of helium-ion bombardment on the optical properties of ZnO nanorods/p-GaN light-emitting diodes

Light-emitting diodes (LEDs) based on zinc oxide (ZnO) nanorods grown by vapor-liquid-solid catalytic growth method were irradiated with 2-MeV helium (He+) ions. The fabricated LEDs were irradiated with fluencies of approximately 2 × 1013 ions/cm2 and approximately 4 × 1013 ions/cm2. Scanning electron microscopy images showed that the morphology of the irradiated samples is not changed. The as-grown and He+-irradiated LEDs showed rectifying behavior with the same I-V characteristics. Photoluminescence (PL) measurements showed that there is a blue shift of approximately 0.0347 and 0.082 eV in the near-band emission (free exciton) and green emission of the irradiated ZnO nanorods, respectively. It was also observed that the PL intensity of the near-band emission was decreased after irradiation of the samples. The electroluminescence (EL) measurements of the fabricated LEDs showed that there is a blue shift of 0.125 eV in the broad green emission after irradiation and the EL intensity of violet emission approximately centered at 398 nm nearly disappeared after irradiations. The color-rendering properties show a small decrease in the color-rendering indices of 3% after 2 MeV He+ ions irradiation.

Differential evolution for the optimisation of multi-band white LED light sources

This paper joins the quest for a white-light source based on mixtures of multiple narrow-band light-emitting diodes (LEDs) with the spectrum optimised for high radiant luminous efficacy and good colour-rendering properties. The complexity of the optimisation process increases with the number of LEDs used to create the white-light source. This paper describes an effective approach for mixing narrow-band LED spectra based on differential evolution, a simple and easy to use direct search method. Two MATLAB programs are designed allowing optimisation using the colour-rendering index and colour quality scale systems. Optimal theoretical solutions for four-LED and six-LED mixtures are analysed.

The origin of the red emission in n-ZnO nanotubes/p-GaN white light emitting diodes

In this article, the electroluminescence (EL) spectra of zinc oxide (ZnO) nanotubes/p-GaN light emitting diodes (LEDs) annealed in different ambients (argon, air, oxygen, and nitrogen) have been investigated. The ZnO nanotubes by aqueous chemical growth (ACG) technique on p-GaN substrates were obtained. The as-grown ZnO nanotubes were annealed in different ambients at 600°C for 30 min. The EL investigations showed that air, oxygen, and nitrogen annealing ambients have strongly affected the deep level emission bands in ZnO. It was concluded from the EL investigation that more than one deep level defect is involved in the red emission appearing between 620 and 750 nm and that the red emission in ZnO can be attributed to oxygen interstitials (Oi) appearing in the range from 620 nm (1.99 eV) to 690 nm (1.79 eV), and to oxygen vacancies (Vo) appearing in the range from 690 nm (1.79 eV) to 750 nm (1.65 eV). The annealing ambients, especially the nitrogen ambient, were also found to greatly influence the color-rendering properties and increase the CRI of the as - grown LEDs from 87 to 96.

Structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 and ZnGeN 2:Mn 2+ for field emission displays

Yellowish-orange-emitting ZnGeN 2 and orange-red-emitting ZnGeN 2:Mn were synthesized by a facile and mild gas-reduction–nitridation reaction at 1153 K under NH 3 flow with air-stable raw materials ZnO, GeO 2 and MnCO 3. The structure, composition, morphology, photoluminescence and cathodoluminescence properties of ZnGeN 2 doped with or without Mn 2+ were systematically investigated. Rietveld refinements show that the as-synthesized samples are obtained as single-phase compounds and crystallize as an orthorhombic structure with a space group of Pna2 1. The actual chemical composition of the as-prepared ZnGeN 2 determined by energy dispersive X-ray spectroscopy suggests that the Ge vacancy defects probably exist in the host. The SEM image reveals that the Zn 0.99Mn 0.01GeN 2 particles form aggregates ∼500–600 nm in size. The diffuse reflection spectrum and photoluminescence excitation spectrum confirm that the band edge absorption of ZnGeN 2 at low energy is 3.3 eV (∼376 nm). Upon UV light excitation and electron beam excitation, ZnGeN 2 gives an intense yellowish-orange emission around 580–600 nm, associated with a deep defect level due to the Ge vacancy defects, and ZnGeN 2:Mn shows an intense red emission at 610 nm due to the 4T 1g( 4G) → 6A 1g( 6S) of Mn 2+. The unusual red emission of Mn 2+ in tetrahedral Zn 2+ sites is attributed to the strong nephelauxetic effect between Mn 2+ and the surrounding tetrahedrally coordinated nitrogen. The photoluminescence and cathodoluminescence emission colors of ZnGeN 2:Mn have a high color purity of ∼93–98%. These results demonstrate that ZnGeN 2:Mn is a novel, promising red-emitting nitride, potentially applicable to field emission displays with brilliant color-rendering properties and a large color gamut.

Influence of Peak Wavelengths on Properties of Mixed-LED White-Light Sources

The purpose of this investigation is to quantify the influence of the peak wavelength shifts in commercially available LEDs on the characteristics of the mixed-LED white-light sources. For this purpose, a tetrachromatic spectrum was optimized and then subjected to deviations in the peak wavelengths. A total of 882 combinations of peak wavelength values were evaluated, and the results are reported in terms of correlated colour temperature, colour-rendering properties, and radiant luminous efficacy. The results show that there can be significant changes in the characteristics of the source under these conditions. Such changes are highly likely to present problems when dealing with applications where an effective and accurate white-light source is important.

Colorimetry: fundamentals and applications

About the Authors. Series Preface. Preface. Introduction. 1 Light, Vision and Photometry. 1.1 Light. 1.2 Mechanism of the Human Eye. 1.3 Adaptation and Responsivity of the Human Eye. 1.4 Spectral Responsivity and the Standard Photometric Observer. 1.5 Definition of Photometric Quantities. 1.6 Photometric Units. 1.7 Calculation and Measurement of Photometric Quantities. 1.8 Relations Between Photometric Quantities. Note 1.1 Luminous Exitance, Illuminance, and Luminance of a Perfect Diffusing Plane Light Source. Note 1.2 Luminance and Brightness. 2 Color Vision and Color Specification Systems. 2.1 Mechanism of Color Vision. 2.2 Chemistry of Color Vision. 2.3 Color Specification and Terminology. 2.4 Munsell Color System. 2.5 Color System Using Additive Color Mixing. Note 2.1 Colorfulness, Chroma and Saturation. 3 CIE Standard Colorimetric System. 3.1 RGB Color Specification System. 3.2 Conversion into XYZ Color Specification System. 3.3 X10Y10Z10 Color Specification System. 3.4 Tristimulus Values and Chromaticity Coordinates. 3.5 Metamerism. 3.6 Dominant Wavelength and Purity. 3.7 Color Temperature and Correlated Color Temperature. 3.8 Illuminants and Light Sources. 3.9 Standard and Supplementary Illuminants. Note 3.1 Derivation of Color Matching Functions from Guild and Wright's Results. Note 3.2 Conversion between Color Specification Systems. Note 3.3 Conversion into XYZ Color Specification System. Note 3.4 Imaginary Colors [X] and [Z]. Note 3.5 Photometric Quantities in the X10Y10Z10 Color System. Note 3.6 Origin of the Term 'Metamerism'. Note 3.7 Simple Methods for Obtaining Correlated Color Temperature. Note 3.8 Color Temperature Conversion Filter. Note 3.9 Spectral Distribution of Black-body Radiation. 4 Uniform Color Spaces. 4.1 Uniform Chromaticity Diagrams. 4.2 Uniform Lightness Scales (ULS). 4.3 CIE Uniform Color Spaces. 4.4 Correlates of Perceived Attributes. 4.5 Comparing CIELAB and CIELUV Color Spaces. 4.6 Conversion of Color Difference. 4.7 Color Difference Equations Based on CIELAB. Note 4.1 Calculation of Munsell Value V from Luminous Reflectance Y. Note 4.2 Modified CIELAB and CIELUV Equations for Dark Colors. Note 4.3 Other Color Difference Formulas. Note 4.4 Direct Calculation of Hue Difference &delta H. 5 Measurement and Calculation of Colorimetric Values. 5.1 Direct Measurement of Tristimulus Values. 5.2 Spectral Colorimetry. 5.3 Geometrical Conditions for Measurement. 5.4 Calculation of Colorimetric Values. 5.5 Colorimetric Values in CIELAB and CIELUV Uniform Color Spaces. Note 5.1 Spectral Colorimetry of Fluorescent Materials. Note 5.2 Reference Standard for Reflection Measurements. 6 Evolution of CIE Standard Colorimetric System. 6.1 Additive Mixing. 6.2 Subtractive Mixing. 6.3 Maximum Value of Luminous Efficacy and Optimal Colors. 6.4 Chromatic Adaptation Process. 6.5 von Kries' Predictive Equation for Chromatic Adaptation. 6.6 CIE Predictive Equations for Chromatic Adaptation. 6.7 Color Vision Models. 6.8 Color Appearance Models. 6.9 Analysis of Metamerism. Note 6.1 Color Mixing Rule. Note 6.2 Lambert-Beer Law. Note 6.3 Method for Calculating the Maximum Value of the Luminous Efficacy of Radiation. Note 6.4 Method for Calculating Optimal Colors. Note 6.5 Method for Obtaining Fundamental Spectral Responsivities. Note 6.6 Deducing von Kries' Predictive Equation for Chromatic Adaptation. Note 6.7 Application of von Kries' Equation for Chromatic Adaptation. Note 6.8 Application of CIE 1994 Chromatic Adaptation Transform. Note 6.9 Theoretical Limits for Deviation from Metamerism. 7 Application of CIE Standard Colorimetric System. 7.1 Evaluation of the Color Rendering Properties of Light Sources. 7.2 Evaluation of the Spectral Distribution of Daylight Simulators. 7.3 Evaluation of Whiteness. 7.4 Evaluation of Degree of Metamerism for Change of Illuminant. 7.5 Evaluation of Degree of Metamerism for Change of Observer. 7.6 Designing Spectral Distributions of Illuminants. 7.7 Computer Color Matching. Note 7.1 Computation Method for Prescribed Spectral Distributions. Appendix I Basic Units and Terms. AI.1 SI Units. AI.2 Prefixes for SI Units. AI.3 Fundamental Constants. AI.4 Greek Letters. Appendix II Matrix Algebra. AII.1 Addition and Subtraction of Matrices. AII.2 Multiplication of Matrices. AII.3 Inverse Matrix. AII.4 Transpose Matrix. Appendix III Partial Derivatives. Appendix IV Tables. References. Bibliography. Index.

Influence of junction temperature on chromaticity and color-rendering properties of trichromatic white-light sources based on light-emitting diodes

Trichromatic white-light sources based on light-emitting diodes (LEDs) offer a high luminous efficacy of radiation, a broad range of color temperatures and excellent color-rendering properties with color-rendering indices (CRIs) exceeding 85. An analysis of the luminous efficacy and CRI of a trichromatic light source is performed for a very broad range of wavelength combinations. The peak emission wavelength, spectral width, and the output power of LEDs strongly depend on temperature and the dependencies for red, green, and blue LEDs are established. A detailed analysis of the temperature dependence of trichromatic white LED sources reveals that the luminous efficacy decreases, the color temperature increases, the CRI decreases and the chromaticity point shifts towards the blue as the junction temperature increases. A high CRI>80 can be maintained, by adjusting the LED power ratio so that the chromaticity point is conserved.

An evaluation of the Hunt94 color appearance model under different light sources at low photopic to low mesopic light levels

AbstractColor appearance models allow for the quantification of color appearance under a variety of viewing conditions. Such models may ultimately provide a measure for accurate assessments of the color‐rendering properties of light sources. This article evaluates the Hunt94 color appearance model using a new set of color‐naming and magnitude‐rating data. At one photopic level (10 cd/m2), the evaluations showed that for a xenon lamp and an enhanced metal halide lamp that have chromaticities and spectra close to an equal energy spectrum, the Hunt94 model provided good predictions of the primary and secondary color names and hue magnitudes for a wide range of color chips under the two illuminants. However, for other light sources the Hunt94 model predictions deviated considerably from the evaluations. Three modifications were applied to the Hunt94 color appearance model to predict color‐naming and magnitude‐rating data better for all light sources. The modified Hunt94 model gave good predictions (correlation coefficients r ∼ 0.95) of the secondary hue magnitude of the color chips used in the experiment at photopic light levels (10 cd/m2 and 1 cd/m2 background luminances) under “white” light sources. However, the modified model was still unable to predict color appearances at low mesopic light levels (0.1 cd/m2 and 0.01 cd/m2). © 2005 Wiley Periodicals, Inc. Col Res Appl, 30, 107–117, 2005; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/col.20088

各種光源の下での色の見え方と演色性に関する研究

各種光源の下での色の見え方と演色性に関する研究

光植物工場経済化のための新しい照明方法

By a proposed theory of an incomplete integrating sphere, illuminance is calculated for efficient photon flux utilization. A practical theoretical model is proposed to estimate the degree of illuminance enhancement.New high-pressure sodium lamps of high color-rendering properties are equipped within the integrating sphere, which yield a considerable gain in the plant factory management. Infrared wavelength component is attributed to this improvement, indicating that the PPFD concept is not sufficient for describing the real growth condition, as well as the power efficiency.By extending the result of utilizing the high color-rendering lamp and the integrating sphere, a considerable improvement in the energy economics of the plant factory is attained than in the author's previous reports. Also to apply to the energy system with a solar power generator, possibility of a self-sustained power system is clearly suggested.

Comparison among Several Methods of Specifying Colour Rendering Properties

Comparison among Several Methods of Specifying Colour Rendering Properties

The LLAB (l:c) colour model

A new colour model, named LLAB(l:c) is derived. It includes two parts: the BFD chromatic adaptation transform derived by Lam and Rigg, and a modified CIELAB uniform colour space. The model's performance was compared with the other spaces and models using the LUTCHI Colour Appearance Data Set. The results show that LLAB(l:c) model is capable of precisely quantifying the change of colour appearance under a wide range of viewing parameters such as light sources, surrounds/media, achromatic backgrounds, sizes of stimuli, and luminance levels. It had a similar performance as that of the Hunt colour appearance model. The LLAB(l:c) model was also tested using various colour difference datasets. The model gave a similar performance as the state-of-the-art colour difference formulae such as CMC, CIE94, and BFD. This performance is considered to be very satisfactory, and the model, therefore, should be considered for field trials in applications such as colour specification, colour difference evaluation, cross-image reproduction, gamut mapping, prediction of metamerism and colour constancy, and quantification of colour-rendering properties. The model does not give predictions for chroma (as distinct from colourfulness), or for brightness, and it does not include any rod response. © 1996 John Wiley & Sons, Inc.

Method of Measuring and Specifying Colour Rendering Properties of Light Sources, CIE Publication 13.3‐1995, Central Bureau Of the CIE, Vienna, Austria, 1995,20 pp, $76 (members)/$l14 (nonmembers)

Color Research & ApplicationVolume 20, Issue 3 p. 212-212 Review Method of Measuring and Specifying Colour Rendering Properties of Light Sources, CIE Publication 13.3-1995, Central Bureau Of the CIE, Vienna, Austria, 1995,20 pp, $76 (members)/$l14 (nonmembers) First published: June 1995 https://doi.org/10.1002/col.5080200313Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article.Citing Literature Volume20, Issue3June 1995Pages 212-212 RelatedInformation

目立ち感に基づく光源の演色性評価方法

目立ち感に基づく光源の演色性評価方法