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Considering that the existing color quality (CQ) metrics for light sources cannot correlate well with the subjective evaluation, in an immersive environment equipped with a multichannel LED light source, a psychophysical experiment by categorical judgment method was carried out to assess the three perception-related CQ attributes of light sources in terms of naturalness, colorfulness, and preference. The experiment collected the subjective responses to these attributes of up to 41 metameric spectra at each of four test correlated color temperatures (CCTs) ranging from 2800 to 6500 K, which covers the usual white-light range for general lighting. The results indicate that preference exhibits relatively high correlation with naturalness and colorfulness, and naturalness is weakly related to colorfulness. Besides, 20 typical CQ metrics were adopted to examine their validity in characterizing the subjective data, confirming their limited performance. Meanwhile, the underlying relationship of these metrics and the subjective data was also analyzed by the multidimensional scaling, revealing that almost all metrics can correspond to one attribute of naturalness, colorfulness, and preference, and that the saturation level is identified as a critical factor affecting these attributes. Based on these results, a unified CQ model was developed with a multiple nonlinear regression equation combining the Illuminating Engineering Society of North America color rendition method. The model accords satisfactorily with the subjective evaluation, while being applicable to a wide range of CCTs.

This note points out additional funding information that was not added to Appl. Opt.56, 1962 (2017).APOPAI1559-128X10.1364/AO.56.001962.

The trade-off between the color fidelity index (Rsubf/sub) released recently by the Illuminating Engineering Society of North America (IES) and luminous efficacy of radiation (LER) was investigated by adjusting the peak wavelengths, spectral widths, and intensities of four-channel LEDs utilizing a multiobjective optimization algorithm based on differential evolution in the correlated color temperature (CCT) ranging from 2800 to 6500 K for general lighting. The results indicate that Rsubf/subat a specific LER value decreases with the increasing CCT, and vice versa, and that Rsubf/subhas significant improvements over the Commission Internationale de l'Eclairage (CIE) color rendering index (CRI) in avoiding spectral gaming and evaluating the light sources even with negative CIE general CRI (Rsuba/sub). Further, the optimal peak wavelengths with regard to Rsubf/subwere identified as 629 nm, 568 nm, 504 nm, and 447 nm, yielding high color rendering in terms of Rsubf/sub(93∼94) and Rsuba/sub(95∼97) and relatively excellent LER (299 lm/W∼339 lm/W) over a wide range of CCTs from 2800 to 6500 K. This suggests that Rsubf/subcan be compatible with Rsuba/sub, making it possible to obtain a common set of optimal peak wavelengths for Rsubf/suband Rsuba/sub. Besides, the IES method could assess saturated red and skin tones more fairly than the CIE CRI. With a practical 17-channel LED array covering the resulted four optimal peak wavelengths, the improvements of the IES method over the CIE CRI were validated further.

The methods were proposed to design the spectra of light sources with multi-channel LEDs based on a differential evolution (DE) algorithm. Specifically, to produce a desired illuminance level while matching a specific spectrum, a matching method combining the DE algorithm and photometry was verified by matching the Commission Internationale de l’Eclairage (CIE) standard illuminants A and D65 at the two desired illuminance levels (500 and 1000 lx) with a multi-channel LED array. Furthermore, considering that correlated color temperature (CCT), illuminance, and color rendering are of practical importance to general lighting, on the basis of photometry and colorimetry, the DE algorithm integrating a mechanism dealing with constraints was developed to optimize the CIE general color rendering index of light sources under a joint target of CCT and illuminance. Sixteen selected targets (eight CCTs from 2800 to 6500 K at 500 and 1000 lx, respectively) were realized with the LED array. The results indicate that the relative errors of CCT and illuminance are less than 0.7% and 1.5%, respectively, while achieving excellent or even perfect color rendering. These methods also enable a practical tool for smart and dynamic lighting.