The effect of correlated colour temperature and wall luminance on spatial brightness and scene preference in a windowless office setup

This study explores the impact of wall luminance and correlated colour temperature (CCT) on the observers’ brightness perception and scene preference in a controlled, windowless office environment. A two-interval-forced-choice experiment was conducted with the 20 lighting scenes derived from five CCTs (2500–10 000 K) and four luminances (12–120 cd/m²). The results from 20 observers showed that a higher wall luminance significantly increased brightness. At equal luminances, different CCT values had no significant effect on brightness, consistent with some reports that CCT is not a reliable predictor of brightness when other photometric factors are held constant. Scene preference increased as wall luminance increased to approximately 72 cd/m², but a further increase in wall luminance to 120 cd/m² had no significant impact on preference. As the CCT increased from 2500 K, the preference increased up to approximately 4000 K, followed by a substantial decline from 5715 to 10 000 K.