Statistical Approach to Color Quality of Solid-State Lamps (original) (raw)
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International Journal of Engineering and Technology, 2017
Nowadays, there are many metrics to determine the color rendering provided by a light source. The Color Rendering Index is the most widely metric used to determine the accuracy of a light source, according to eight color samples. However, this metric does not allow a proper measurement for LED lamps. Recently, the Color Quality Scale was defined, extending the color samples selected by previous metrics in order to improve the analysis of LED lamps. However, the results of both metrics for a low correlated color temperature use as reference the Standard Illuminant A, that is to say, the color rendering of an incandescent lamp, which does not represent the real conditions of the natural color rendering. Currently, new metrics appears, such as the TM-30-15, based on 99 color samples and a complex calculation. According to this context, a new metric is proposed, based in the Spectral Power Distribution of daylighting. The daylight spectrum is corrected by the photopic luminosity function, as well as the spectrum of the light source sample. Both corrected spectrums are compared in order to determine the Daylight Spectrum Index. This new metric represents a better definition of the LED lamps for a high correlated color temperature, as can be deduced from the analyzed surveys.
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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
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Impact of cross-regional differences on color rendition evaluation of white light sources
In a study, involving laboratories from seven geographic regions, the memory colors of eleven familiar objects were investigated. Based on that study, one global and seven regional memory color rendition indices (MCRIs) are created and the impact of cross-regional differences on the evaluation of color rendition was investigated. A first analysis focuses on the impact on MCRI index values by comparing the regional index values, calculated for 401 light sources, with those of the global index. A second analysis examines the impact on predictive performance in terms of the visual appreciation and naturalness of rendered objects colors as evaluated in respectively twenty-one and fifteen experiments published in literature. Both analyses show that, although there are small differences in absolute level of color rendition, the regional metrics are generally comparable in terms of predicting light source rank order and correlation with visual data. Therefore, ànd considering between-region variability to be smaller than or of the same size as the within-region variability, a globally valid memory color rendition metric can be proposed without introducing substantial errors. Finally, Smet's Rm index, obtained using real objects, is suggested as a good approximation to that globally valid metric.