Effects of General and Task Lighting on Subjective Perception and Work Performance: Empirical Study in an Office

Lighting accounts for a large proportion of building energy use. Task lighting is effective in saving lighting energy consumption and found to improve productivity in factories, but its effects in offices remain unknown. This study aims to investigate the effects of general and task lighting on office occupants’ satisfaction, alertness, mood, and performance in simple and complex tests. A within-subject design involving 2 lighting condition (100% general lighting vs. 70% general + 30% task lighting) × 2 task type (paper-based vs. computer tasks) was adopted. The work-plane illuminance and the equivalent melanopic illuminance were controlled at the same level in two lighting conditions. The lighting power was reduced by 16.7% when introducing task lighting. 28 subjects participated in this empirical study. The results showed that different lighting conditions had no significant impact on alertness. Introducing task lighting would suppress positive mood, but improve work performance. The respond speed in simple tasks was significantly improved by 4.3%-8.5% and the correct rates in complex assessments increased by 6.2%. These findings highlight that the combination of general and task lighting reduces power consumption and benefits work performance. However, its suppression on the positive mood also needs to be considered in the lighting design.