A study of circadian lighting in an open-plan office building in Bangkok

Abstract

This study aims to explore and compare the illumination levels in office building workspaces and evaluate the effectiveness of lighting in stimulating the circadian system according to the Well Building Standard criteria. Additionally, the study aimed to evaluate sleep quality and daytime sleepiness based on light exposure in the workspace using the Pittsburgh Sleep Quality Index (PSQI) and the Epworth Sleepiness Scale (ESS). Illuminance (Lux) measurements were taken at desk height, and light color temperature (Kelvin) was assessed at individuals' regular seating positions.

The findings indicate that the illumination levels in the workspace do not meet the Well Building Standard criteria for circadian rhythm stimulation. The average illumination levels across the three floors (23, 25, and 27) were 460.97 lux, or 207.44 melanopic lux, which is suitable for general building use but inadequate for circadian rhythm stimulation. Optimal illumination levels that effectively influence the circadian rhythm in workspaces should be ≥ 560 lux (fluorescent) or 250 melanopic lux for at least four hours per day or throughout the year. This result aligns with the sleep quality and daytime sleepiness assessments, where 71% of participants reported poor sleep quality, and 46% experienced excessive daytime sleepiness. These findings correlate with the limited use of natural light and reliance on artificial fluorescent lighting, which is ineffective for circadian rhythm stimulation. Therefore, office management should focus on improving the lighting environment to effectively stimulate the circadian rhythm, promoting well-being and enhancing productivity for the building occupants.