Balancing Glare and Circadian Stimulus with Shade Device Simulation

Abstract

Daylight utilization in the built environment is highly valued for its dual benefits: energy conservation and enhancing human health. Yet, achieving visual comfort is challenging due to the uneven distribution of light levels, particularly in buildings with deep spaces. When encountering glare issues near windows, shading devices used to mitigate glare often compromise daylight exposure and its circadian stimulus elsewhere, impacting the healthy sleep-wake cycles known as circadian rhythms. Recent research has underscored the significance of photoreceptors in the eyes and skin, which govern circadian rhythms across species. Among these, intrinsically photosensitive retinal ganglion cells (ipRGCs) are pivotal in reacting to specific light spectrums, thereby becoming a focal point in daylighting design strategies. Considering that humans spend approximately 90% of their lifetime indoors, the quality of circadian lighting is paramount for wellbeing. Addressing the conflict between glare reduction and circadian health, this study identifies a theoretical balance. 2657 lux of vertical illuminance at the eye typically precedes glare, while the WELL v2 standard specifies a minimum of 150-275 equivalent melanopic lux (EML) for adequate circadian entrainment. Moreover, human visual and non-visual responses peak at green and blue wavelengths respectively. This difference in spectral sensitivities provides a clue to the equilibrium between visual comfort and circadian stimulus. This research proposes a simulation-based approach to design shade fabric configurations that achieve a balance between visual comfort and circadian health. The goal is to effectively calibrate light intensity and color spectrum, thereby harmonizing the daylight entering through windows. Such an equilibrium can furnish spaces with holistic daylighting solutions that address the interplay between energy efficiency, visual comfort, and circadian stimulus, thus promoting occupant health and productivity.