Evaluation of Several Different Types of Uniformity Metrics and Their Correlation with Subjective Perceptions

Abstract

This study aimed to identify how different types of uniformity indicators function to evaluate the uniformity of lighting, such as the minimum-to-average ratio (Min:Avg), the coefficient of variance (CV), entropy uniformity (EU, introduced in the article), and a pattern vision-based indicator (UHVS). Two experiments, a pair-wise comparison and a seven-point scale subjective evaluation, were performed to study the advantages and disadvantages of uniformity indicators. Thirty abstract patterns simulated from architectural illumination scenes were applied in the experiments. The results of the pair-wise comparison experiment reveal the following: the uniformity ranking and the sorting of uniformity indicator values obeyed a linear relationship; EU and UHVS exhibited superior performance, with an adjusted R2 of 0.96; the CV was satisfactory, with an adjusted R2 of 0.91; and the Min:Avg was somewhat acceptable, with an adjusted R2 of 0.70. The results of the seven-point scale subjective evaluation experiment demonstrated that ratings were linear with the Min:Avg, CV, and UHVS, of which UHVS was most consistent with human ratings of acceptability, with an adjusted R2 of 0.96; the CV was acceptable, with an adjusted R2 of 0.85; and the Min:Avg was the worst, with an adjusted R2 of 0.71. The subjective evaluation rating and the EU indicator exhibited an exponential relationship, with an adjusted R2 of 0.95, rather than a linear relationship. Different metrics have their own characteristics and may be suitable for different applications.