Effectiveness of Light Source Efficiency for Characterization of Colored Surface Luminance

ABSTRACT The lamp spectrum and the surface reflection both contribute to the luminous efficiency of the illuminated object. Hence, it may not be comprehensive to evaluate the luminous efficiency in a lighting environment only through the metrics with respect to lamps. Previous studies have investigated the effect of surface reflection on luminous efficiency, but few quantitative metrics have been proposed so far. In this study, statistical analysis and a validation experiment were conducted to investigate the extent to which the luminous efficacy of radiation (LER) determines the luminous efficiency of a colored surface. The correlation analysis was performed based on an index of the surface spectral reflectance, namely, the spectral reflectance luminous efficacy of radiation (SRLER). The correlation between the SRLER and LER varied with respect to the hues and saturation levels of the colored objects. In particular, highly linear correlations were observed in slightly saturated and highly saturated green, yellow, and purple-blue samples but not in highly saturated reddish samples. This suggests that when the illuminated environment contains a large portion of highly saturated reddish objects, the effectiveness of the LER is dependent on the spectral selectivity of the colored surface. The findings of this study contribute significantly to the comprehensive design of light source spectra and energy saving in actual lighting scenarios.