Accuracy comparison of spatial brightness evaluation metrics under indirect lighting conditions

Among existing spatial brightness (SB) metrics, mean room surface exitance (MRSE), average luminance in a horizontal band with a width of 40°(L_av,B40), and indirect corneal illuminance (E_cor,i) have received extensive attention. However, these metrics employ fundamentally different weighting strategies for contributions of light from various spatial regions, making it important to directly compare their accuracy. This study recruited 36 participants and employed four classical psychophysical methods recommended in CIE 212:2014 to evaluate the performance of the three metrics under controlled indirect lighting scenes with different spatial light distributions. Results consistently showed that the E_cor,i metric aligned most closely with subjective SB evaluations and achieved higher accuracy than the MRSE and L_av,B40 metrics. Moreover, lighting distributions closer to the center of the visual field were found to carry a higher weight in SB perception, a characteristic effectively captured by the E_cor,i. These findings provide empirical evidence for the potential advantage of E_cor,i over MRSE and L_av,B40 in reflecting subjective SB perception under the indirect lighting conditions.