A Daylight Assessment on Visual and Nonvisual Effects of Light Shelves: A Human-centered Simulation-based Approach

Abstract

The contribution of daylight to a comfortable environment for occupants has been the subject of studies for years. Light shelves are known as daylight redirecting systems to enhance indoor daylight conditions. Although several research papers have focused on their daylight performance, there is a lack of studies on the performance of light shelves on circadian rhythm. In this context, daylight's biological effects on human beings have been under investigation. Therefore, this paper aims to evaluate the performance of light shelves in terms of visual and nonvisual effects of daylight, including circadian stimulus, visual comfort, and task performance through a multi-criteria human-centric evaluation. To this end, the authors set three following conditions if a model could provide simultaneously, the occupants would be in a comfortable space both visually and non-visually: 75% workstations with Equivalent Melanopic Lux> 250 EML concurrently with Vertical Photopic illuminance < 1500 lux, and Photopic illuminance on working plane > 300 lux. Accordingly, the light shelves with various depths, states, and orientations were simulated by ALFA to evaluate the comfort of occupants in office space over working hours. The results indicated that although applying light shelves impacted the metrics, the enhancements were minor compared to a conventional window, specifically on EML. In detail, inadequate EML levels were observed in all orientations on the simulation days. Besides, changes in the photopic illuminance at the eye and workstations levels were not substantial. Finally, the paper presents a case study that showcases simulation techniques that focus on daylighting and circadian rhythm.