Modelling a multicomponent radiation source with controllable chromaticity (original) (raw)
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The CIE color rendering (fidelity) index (CRI) has remained unchanged for over four decades. Most, if not all, of its components could be updated to more state-of-the-art methods. One of the most critical components of any color rendering (fidelity) metric is the test sample selection. This article therefore addresses the importance of uniform sampling of wavelength space to avoid selective optimiza-tion—that is, taking advantage of the unequal contributions of different wavelength regions to the general color rendering score—of light source spectral power distributions. It summarizes the development of a mathematical sample set with undistorted spectral sensitivity, the HL17 set. The set is used in a recently proposed update, the CRI2012 general color rendering index. To assess the impact of the spectrally uniform sample set on color fidelity scores, the CRI2012 index values for each of a set of 139 lamps were compared with those of the CIE CRI. In addition, the impact of updating the other components was investigated. A mean and maximum absolute difference of respectively 5.9 and 21.8 index units were found between the CRI2012 and CIE CRI, although the largest part—respectively 4.03 and 19.7 index units—was shown to be the result of updating the color difference engine and the switch to the CIE 10 • observer. The analysis also indicated possible past spectral selective optimization of some warm-white tri-band fluorescent sources for high luminous efficacy of radiation (LER) and (just) sufficient CIE R a values by taking advantage of the spectral nonuniformity of the CIE reflectance set. Adopting a spectrally uniform sample set in a color rendering metric therefore has important practical implications when designing light source spectra. Finally, possible updates and further improvements of the CRI2012 are briefly mentioned.
Toward a Replacement of the CIE Color Rendering Index for White Light Sources
LEUKOS, 2015
The CIE color rendering (fidelity) index (CRI) has remained unchanged for over four decades. Most, if not all, of its components could be updated to more state-of-the-art methods. One of the most critical components of any color rendering (fidelity) metric is the test sample selection. This article therefore addresses the importance of uniform sampling of wavelength space to avoid selective optimization-that is, taking advantage of the unequal contributions of different wavelength regions to the general color rendering score-of light source spectral power distributions. It summarizes the development of a mathematical sample set with undistorted spectral sensitivity, the HL17 set. The set is used in a recently proposed update, the CRI2012 general color rendering index. To assess the impact of the spectrally uniform sample set on color fidelity scores, the CRI2012 index values for each of a set of 139 lamps were compared with those of the CIE CRI. In addition, the impact of updating the other components was investigated. A mean and maximum absolute difference of respectively 5.9 and 21.8 index units were found between the CRI2012 and CIE CRI, although the largest part-respectively 4.03 and 19.7 index units-was shown to be the result of updating the color difference engine and the switch to the CIE 10 • observer. The analysis also indicated possible past spectral selective optimization of some warm-white tri-band fluorescent sources for high luminous efficacy of radiation (LER) and (just) sufficient CIE R a values by taking advantage of the spectral nonuniformity of the CIE reflectance set. Adopting a spectrally uniform sample set in a color rendering metric therefore has important practical implications when designing light source spectra. Finally, possible updates and further improvements of the CRI2012 are briefly mentioned.
Mathematical Model of Colorimetry
Bulletin of Kyiv Polytechnic Institute. Series Instrument Making, 2017
The work is devoted to the analysis of methods of mathematical modeling, one of the most important in human life-the organ of vision, which accounts for more than 90% of all incoming information about the external world. The human eye is a unique (natural) natural apparatus. Therefore, the principles of his work have long attracted the attention of scientists. At the heart of the tasks posed in this paper were questions closely related to the theory of human perception of color. Still I.Newton the ground for creation of linear model of color vision was prepared. For the first time one of such models was suggested by T. Young. But T. Young was interested not so much in the psychophysical side of the phenomenon as in the physiological aspect, therefore, from the point of view of psychophysics, his results look like an episode. The most consistent continuation of Newton's ideas was Maxwell, who attempted to experimentally determine a specific kind of weight functions that characterize the sensitivity of the eye to radiation with different wavelengths, called spectral sensitivity functions of the eye. The first attempt to create an axiomatic theory of the eye was undertaken by Grassmann. Relying on Newton's results and his idea of a "null-organ", he formulated the laws of color vision-the law of additivity, the law of three-dimensionality, the law of continuity. Starting from these laws, Schrödinger attempted to derive Newton's transformations from them in a purely formal way. However, the imperfection of the mathematical algorithm used by him and the formulation of the laws of vision did not allow him to do this correctly enough. But on the whole, Schroedinger's research should be seen as an essential step in the development of the theory of vision. Based on the analysis of existing mathematical methods of vision research, the present work accepts the interpretation of input signals in the form of Hilbert spaces. The main reason for this is as follows. As studies of sensory systems show, the description of the work of sense organs leads us to linear functionals whose general form is known in Hilbert spaces or in spaces of type Lp. The authors of the paper propose a method and an apparatus for colorimetric measurements. The main element of the color tone recognition device is a sensor (color sensor) in which to increase the sensitivity and reliability of measurements, as well as simplify the tuning process, not three, but more (number) photodetectors are used.
. Mathematical Modeling of the Colour Characteristics of an Electroluminescent Layer Emission
Introduction. The electroluminophors - substances which radiate visible light under the influence of an electric field, are used in the modern devices as displays and indicators. The colour pallette of the pure electrolumophors emission is restricted. In the case with elecffolumonophors of pre-puncture type (dust substances, forming a thin emitting layer) it is possible to achieve a considerable colour variety by mixing luminophors with different emission colours. As a result of the complex dependence of the emission on a number of factors, the colour of the final growing structure, made by mixing different types of electroluminophors (for example, with green, red and blue emission colour), it is unpredictable. Our aim is to develop a method which can predict the ratio of luminophors mixture which could glow whit a colour, set in advance. Goal. This work describes a part of above mentioned method, namely to model dependency of the spectra of green emitting electroluminescent structures on power supply frequency and voltage, concentration of the elektroluminofor in the structure, absobtion coefficient of the electroluminescent layer and the thickness of the electroluminescent layer. Material and method. A set of a green light emitted electroluminescent structures, which spectra was measured in different combinations of frequency and voltage of the power supply. Results. Gauss curve was used as a model of spectra. Three parameters determine the form of the curve. Each of them depends on frequency and voltage some of them depend on concentration, absorbtion coefficient and thickness, too. The curve parameters polynomial regression functions on the parameters of the layer and the power supply were determined. Thus, the curve form becomes function on the layer parameters.
Improved Method for Evaluating and Specifying the Chromaticity of Light Sources
LEUKOS, 2022
This article describes a method for calculating and specifying light source chromaticity using the International Commission on Illumination (CIE) 2015 10° color matching functions (CMFs), which, according to analysis of existing psychophysical experiment data, can reduce visual mismatch compared to specifications based on the traditional CIE 1931 2° CMFs in architectural lighting applications. Specifically, this work evaluates, documents, and recommends for adoption by lighting standards organizations a supporting system of measures to be used with the CIE 2015 10° CMFs: a new uniform chromaticity scale (UCS) diagram with coordinates (s, t), a measure of correlated color temperature (CCTst), and a measure of distance from the Planckian locus (Dst). It also presents options for updating nominal classification quadrangles. A complete method of this nature has not yet been standardized, which may be contributing to the slow uptake of the CIE 2015 CMFs. The proposed tools are analogous to u, v, CCT, Duv, and the American National Standards Institute (ANSI) C78.377 chromaticity specifications that are all currently defined in the CIE 1960 UCS diagram using the CIE 1931 2° CMFs. While conceptually equivalent, the differences between the current standard method and the proposed st system are important for reducing unintended visual mismatch in the chromaticity of light. The implications of changing chromaticity specification methods are identified by a comparison over a diverse set of real light source spectral power distributions.
Color appearance in multispectral radiosity
In closed environments, especially in bright colored interiors, there occurs a significant change of saturation and some shifting of hue of originally selected colors. This is due to multiple light inter-reflections. The human vision mechanism partly reduces this effect thanks to the change of the reference white. We use in this paper a multispectral radiosity method to describe and compute the physical effects. We also use a color appearance model, the new and powerful CIECAM02 model, to compute the perceptual aspects. The CIECAM02 includes the luminance and chromatic adaptation effects, and it has compact forward and inverse transformation formulas. The input data for the color appearance model is ensured by computing the radiosity solution, thereby there are known both the spectral radiance for every viewpoint and view direction and the spectral irradiance on every patch of the scene. Nearly all of earlier global illumination approaches ignored the often strong changes of originally selected colors. This paper supports the color environment design. Using the presented method it is possible the selection or mixture of paints to achieve, after the physical and perceptual effects, a color appearance previously selected under standard viewing conditions in a color atlas.
About color rendition of light sources: The balance between simplicity and accuracy
Color Research and Application, 2010
Most descriptions of the color-rendering properties of light sources are based on the calculation of color differences for a number of test colors between the light source and a reference source. The CIE color-rendering index (CRI) is a single number based on the average color difference for eight test colors. Ever since its introduction the CRI has been discussed and several suggestions have been made to improve the description of the CRI such as color preference index, color appearance data and color discrimination index. New lighting technologies such as LEDs can have spectral power distributions consisting of narrow spectral bands in the red, green and blue region of the spectrum. There are indications that the CRI does not always provide a reliable description of the color-rendering properties of these LED based light sources.In this article the principal elements of the CRI calculation are analyzed and their influence on the color-rendering description will be discussed. The focus of the analysis has been on the selection of object colors. Principally the color-rendering description of a light source should not depend on the set of colors chosen for the calculation. From our analysis requirements for such color sets are given. © 2010 Wiley Periodicals, Inc. Col Res Appl, 2010
About colour rendition of light sources. The balance between simplicity and accuracy
ABSTRAC The CIE Colour Rendering Index (CRI) is a well-known descriptor for the colour rendering properties of light sources. Being a single number the CRI is a comprehensible figure of merit. The accuracy of the CRI in predicting specific colour rendering aspects is relatively low. CRI is an average of only 8 colours and accounts only for the size of the colour shift. Several new suggestions for an improved description of colour rendering have been done. All these suggestions had one thing in common: the description of colour rendering gets more complicated. In this paper we will present a new way of analysing colour shifts and discuss the effect of the colour sets and the effect of narrow band spectral power distributions on the accuracy and simplicity of colour rendering information.
Optimization of sensor response functions for colorimetry of reflective and emissive objects
IEEE Transactions on Image Processing, 1996
This paper describes the design of color filters for a surface color measurement device. The function of the device is to return the X Y Z tristimulus vector characterizing the color of the surface. The device is designed to measure emissive as well as reflective surfaces. It uses an internal set of LED's to illuminate reflective surfaces while characterizing their color under assumed standard illuminants. In the design of the filters, we formulate a nonlinear optimization problem with the goal of minimizing error in the uniform color space CIE L*u*b*. Our optimization criteria employs a technique to retain a linear structure while approximating the true L*u*b* error. In addition, our solution is regularized to account for system noise, filter roughness, and filter implementation errors. Experimental results indicate average and worst-case