Efficient circadian daylighting: A proposed equation, experimental validation, and the consequent importance of room surface reflectance

Abstract

With the increasing understanding of light's non-visual impact on human circadian system, applying circadian daylighting in buildings becomes attractive. The successful adoption of circadian daylighting requires a considerable amount of light incident at the eyes without causing discomfort glare. Therefore, developing daylighting strategies that can efficiently provide indirect corneal illuminance is a promising approach.An equation is proposed to establish the dependence of daylight-enabled corneal illuminance, especially its indirect component, on room surface reflectance and window-to-wall ratio (WWR). The accuracy of the equation is validated in an artificial sky lab which mimics a fixed overcast sky condition. Experiments using scaled room models with various combinations of interior surface reflectance, WWRs, testing locations and measurement directions prove that the proposed equation is accurate. The results suggest that room surface reflectance plays a dominant role in maximizing indirect corneal illuminance. This is further confirmed by performing a Radiance lighting simulation analysis on daylight-enabled morning-hour Circadian Stimulus in a classroom, which supports the proposed equation as well. This work concludes that the proposed equation can provide quick estimation in circadian daylighting design and that high room surface reflectance is the key to achieve efficient and quality circadian daylighting.