Photobiological Material Systems: Spectrally-Selective Surfaces for the Regulation of Indoor Alertness

Abstract

Color, light, and their interaction within the built environment have always been pertinent spatial and aesthetic factors that architects consider in their work; however, their study has been limited to a primarily perceptual perspective. This thesis studies the relationship between color, light, and design from a physiological perspective, and, in particular, through the lens of newly discovered findings in human neuroscience and photobiology. Those findings pertain to the discovery of light as a promoter of alertness -or sleep- depending on its spectrum, as introduced through the discovery of a non-visual, photosensitive system in the human retina. That system consists of a network of intrinsically photosensitive retinal ganglion cells (ipRGCs) and is responsible for synchronizing human circadian rhythms and a series of associated bodily functions such as sleep/wake cycles and hormone production. The key photopigment that activates that system is melanopsin, a blue-light sensitive photopigment that, depending on the spectra and the illuminance of the light, triggers a biochemical cascade that signals the brain on the synchronization of the body’s daily rhythms. Specifically, melanopsin photoreceptors have a peak light absorption at wavelengths of approximately 480 nanometers.

To date, research in lighting and photobiology has examined alertness and sleep effects mainly in relation to light spectra, overlooking the role of architectural surfaces and materials in the shaping of an environment's photobiological behavior. Moreover, research has not yet addressed photobiological behavior in an adaptive context where interiors are designed to affect both daytime- and nighttime-appropriate spectral content. To address this problem, the thesis proposes Photobiological Material Systems as a design framework for spectrally selective surfaces that, in combination with adaptive lighting infrastructures, can promote alertness effects during the day and sleep-promoting effects during nighttime. The proposed framework is developed through a series of physical and simulation studies of increasing complexity, as well as a contextualization of the studies' results within contemporary theories of color and areas of architectural discourse.

Through the introduction of this new framework, the thesis contributes to the areas of Architectural Design, Lighting Design, and Photobiology in various aspects: at a fundamental level, the thesis produces new knowledge on how spatial elements such as color, light, and surface geometry contribute to an interior environment’s alertness and sleep effects on its occupants; from a standards perspective, it explores the limits of photobiological efficiency of commercially available color swatches when combined with light sources of different spectra; at an application level, the thesis introduces a new, science-grounded and biology-driven framework for using color in design and architecture.