Study on the impact of illuminance on comfort and productivity in Japanese office buildings

The lighting environment in office workspaces plays a vital role in influencing both comfort and productivity. Maintaining optimal illuminance level is crucial for enhancing work performance. Previous studies have explored elements such as brightness perception, users’ lighting preference, productivity, and perceived comfort in response to changes in illuminance. However, research on comfortable illuminance levels remains limited. This study measures illuminance conditions in selected office environments while simultaneously examines the relationship between brightness perception, lighting preference, and productivity. It also aims to identify a comfortable illuminance range for office workers, aiming for both well-being and energy efficiency. The monthly field survey was conducted in 23 office buildings in the Kanto region of Japan. The number of responses collected was 4,660 for survey 1 and 2,637 for survey 2, totaling 7,297 responses. Results showed that regardless of the average indoor illuminance, workers were satisfied with the current lighting conditions in their offices. Moreover, both brightness perception and lighting preference exhibited a positive correlation with productivity which was highest when workers perceived the lighting as moderately bright indicating preference to the current lighting level. During this time, the indoor illuminance was found to be between 500 to 700 lx. Although the overall impact of illuminance was not high, they did influence individual comfort and productivity of occupants.