No abstract

No abstract

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.

Light environment’s non-visual effects influence people’s health and work efficiency. However, considering non-visual requirements in addition to traditional visual requirements may significantly increase lighting energy consumption. This study utilized simulation software to explore energy saving potential of changing the direction of the luminaire. A model of a single-person office with the luminaire attached to the ceiling right above the workstation was built in ECOTECT. Vertical eye-level illuminance and horizontal work-plane illuminance were calculated with luminaires of different luminous fluxes and elevation angles from downward vertical (0°-180° at an interval of 10° on both sides) using RADIANCE. Furthermore, six cases of different lighting requirements and light correlated color temperatures were considered. Based on the illuminance-versus-luminous flux coefficients obtained from simulation results, luminous fluxes were calculated to fulfill both visual and non-visual requirements under different elevation angles in all cases. It was found that compared to traditional lighting design with the luminaire facing vertically downwards, turning the luminaire at an elevation angle of 50° reduced the required luminous flux by up to 22.7%, which would benefit energy savings. Therefore, changing the direction of the luminaire has the potential to improve office lighting energy efficiency when considering both visual and non-visual requirements.