Alertness in work environments - on the role of indoor daylight exposure

Light enables to see the world around us, while playing a key role in our biological functioning. During the last decades, light has become an important research topic for chronobiologists and neuroscientists, and their findings are increasingly interwoven with architectural research.

Based on existing studies pertaining to ipRGC-influenced effects of light, there is a general consensus that higher intensities and bluer conditions seem to promote alertness and/or cognitive functioning, and affect circadian regulation. In that sense, daylight – which is freely delivered and under which we have evolved – seems to have key properties when it comes to impacts on body functioning. Yet, the knowledge we have gathered so far is oftentimes based on either static or well-controlled and somehow extreme electric lighting conditions that have been mainly explored in the laboratory confinement, and which do not necessarily represent reality. Considering that current life and workstyles are driving us to spend more time indoors, the importance of understanding the added value of indoor daylight exposure in our daily routines seems unquestionable. Answering to what extent such biological responses may or may not be also observable under more realistic conditions will be the main focus of the work presented in this thesis.

More specifically, our research explores the cause-effect relationship between indoor daylight exposure and daytime human functioning in terms of alertness, attention and arousal. Ultimately, the idea is to gain a better understanding of the role of architectural design in daylight provision from a psycho-physiological perspective. Three user studies were conducted in learning spaces to understand both the combined and individual effects of varying daylight spectrum, its intensity, the duration and the timing of exposure. Second, a further investigation of these effects was conducted through the application of three physiology-based, light-driven mathematical models, so as to get insights about the limitations and potential of experimental data and simulated values in the prediction of alertness. Based on the learnings gained from both perspectives, a functional simulation workflow is proposed for the study of alertness in the context of architectural design.

Overall, the topic of this thesis was to investigate the impact of manipulating the spectrum or intensity of daylight entering an indoor space on its occupants, with a more specific focus on their alertness. The outcomes of the user studies showed that red-impoverished conditions, when compared to unfiltered ones in dim environments, resulted in higher alertness and attentional levels. They also showed that variations in indoor daylight intensity, both under blue-shifted and neutral conditions, led to observable effects on people’s alerting responses. In addition, duration and timing of exposure were shown to have a key role in determining the magnitude of these responses, with longer exposures and afternoon sessions being subjectively reported as more influential.

To advance knowledge in the field of daylight integration in the built environment for supporting occupants’ health and well-being with an evidence-based approach, lighting requirements should continuously be refined according to the latest knowledge available. Insights from this thesis can be seen as a first step towards anticipating the impact of daylighting strategies on human-centric performance.