Comparison between the use of daylight and electric light to support building occupants’ health

Project supervisors: Dr. Clotilde Pierson – LIPID | EPFL, Prof. Marilyne Andersen – LIPID | EPFL

Office view with daylight compared to office view with electric light

Context

Nowadays, people spend around 90% of their time indoors. This indoor lifestyle does not come without a cost. The World Health Organization has recognized the detrimental effects that the indoor built environment can have on our health and well-being; not only because of indoor air pollution, but also due to a poor exposure to light1. The discovery of a new photoreceptor in the human eye has indeed made us aware of the important role of light in synchronizing our internal body clocks, i.e. our circadian rhythm. Studies have shown that a poor exposure to light is linked to disruption of circadian rhythms, which in turn can lead to sleep disturbance, depression, mental disorders, and increase the risks for other diseases and conditions2. A poor exposure to light has also been shown to impact our alertness, mood, and some neurobehavioral processes3. Such effects of light on human physiology, behaviour, and mood, are often summarised as the non-visual effects of light. Considering that we spend the vast majority of our time indoors, it becomes urgent to anticipate how architectural features and indoor characteristics affect our exposure to light, hence impacting these so-called non-visual effects. Increasing attention should be paid to creating a comfortable and healthy lighting environment in offices, classrooms, or homes, which supports the health and well-being of its occupants.

Objectives

In this broad field of non-visual effects of light, the proposed project focuses on the types of light sources that should be favored in office environments for promoting a proper exposure to light. The goal is therefore to compare the efficiency of different light sources, such as daylight, LEDs, and fluorescent tubes, in providing an exposure to light that supports the health and well-being of occupants. In a first step, the student will collect some measurements of exposure to light under different electric light sources in a typical office layout. Measurements of exposure to light under daylight conditions have already been collected by the supervisors. In a second step, the student will compare the different measured exposures to light for their efficiency in producing beneficial non-visual effects of light. Existing models and indicators to evaluate the non-visual potential of a certain exposure to light will be used. As a last step, the student will put the comparison results in the broader context of building lighting, discussing energy and visual comfort considerations. Deliverables

The student(s) will present their progress and research through: § a midterm presentation (10 min) § a final presentation (20 min) § a written report(accounting for 2/3 of the final grade)

The report and presentations must be in English. Skills, equipment and tools involved

Through this project, the student(s) will gain experience in: § elementary experimental design § sensors calibration and measurement of photometric and radiometric data § data process and analyses through programming language

Previous experience with any of the above is an advantage but not needed. The supervisors will provide initial training to familiarize with the tools needed during the semester. This project shall be carried by 1-2 student(s). Reference

1 WHO Regional Office for Europe. Combined or multiple exposure to health stressors in indoor built environments. Bonn, Germany: World Health Organization, 2014. 2 Abbott SM, Malkani RG, Zee PC. Circadian disruption and human health: A bidirectional relationship. European Journal of Neuroscience 2020; 51: 567–583. 3 Xiao H, Cai H, Li X. Non-visual effects of indoor light environment on humans: A review. Physiology & Behavior 2021; 228: 113195.