Healthy lighting: integrating non-visual responses to light into building simulation

The goal of this thesis is to develop a computer-based lighting simulation framework capable of predicting human non-visual responses to light and to validate novel guidelines that can inform designers about how lighting might affect human non-visual responses in the built environment. The framework consists of four steps, including a mathematical model that accounts for spectral and dynamic variations in light exposure. As a part of the framework, different light exposure patterns are generated to simulate the effects of occupants’ actions, movements, and activities. The results are interpreted based on pre-defined design goals. Light is one of the most significant factors that affect human health and wellbeing in the built environment. Since 2002, when the first reports on the discovery of a novel type of photoreceptor were published, a new field of study started to emerge at the intersection of photobiology and architecture. The novel photoreceptors are the primary mediators of non-visual responses to light in humans, including synchronizing circadian rhythms and directly alerting the brain. These new findings emanating from the photobiology field have sparked a growing interest in the role of lighting design on human health and wellbeing. The novel photoreceptors contain the photopigment meanopsin. Melanopsin is more sensitive to short- wavelength light, with a peak sensitivity that is blue-shifted (λmax ≅ 480 nm), relative to the photopic visual system (λmax ≅ 555 nm), which is dominated by the response of cone photoreceptors. In addition to the difference between the photoreceptors’ spectral sensitivity, researchers have identified intensity, duration/pattern, history, and timing of light exposure as important variables that control the non-visual light response in humans. Considering the blue-shifted sensitivity of the melanopsin-containing photoreceptors, the current recommendations for lighting, which are based mainly on visual criteria, may not provide the necessary amount of light to synchronize important physiological and behavioral rhythms to the 24-hour day. Moreover, a number of recent studies have demonstrated that exposure to bright light can improve alertness, performance, and mood. However, exposures to light at night can disturb circadian rhythms, such as hormone production and sleep-wake cycles, and have been linked to increased risk of cancer. Lighting simulation software tools are designed to evaluate visual requirements and comfort taking into account the stochastic fluctuations linked to the climate and to the behavior of the buildings’ occupants. The evaluation compares simulated light intensity values on a horizontal plane with static threshold values. Since the non-visual system responds slowly to light exposure and adapts to changes in light intensity and spectral composition over much longer time periods than the visual system, the lighting simulation software tools cannot be applied directly to evaluate the non-visual response to light. The response must be evaluated based on dynamic threshold values, which depend on intensity, spectrum, duration, history, and timing of light exposure. Currently, there is no mathematical model that incorporates all five variables to predict the non-visual effects of light on humans. Further, the movements of humans must be simulated to account for the amount of light received at the eye. Thus horizontal sensors on a plane must be replaced with vertical sensors at the eye level that can rotate and move around. The importance of building simulations is growing with increasing complexity of building design and higher performance requirements regarding sustainability. New methods, created at the interface between photobiology and architecture, predicting the non-visual response to light are needed to support design decisions.

Light-driven model for identifying indicators of non-visual health potential in the built environment

María Lovísa Ámundadóttir

This thesis introduces a new approach to characterize and evaluate ocular light exposure based on the discovery of novel blue light-sensitive photoreceptors in the human eye. These photoreceptors are the primary mediators of 'non-visual' responses impacting human health, from resetting the circadian clock to directly alerting the brain. In recent years, studies have found that light at short-wavelengths is more effective than light at longer wavelengths at inducing and suppressing a range of 'non-visual' responses. Although it has been recommended that we approximate the spectral sensitivity of these novel photoreceptors with an action spectra peaking near 490 nm, the optimal approach for quantifying non-visual spectral effectiveness is yet unknown. These novel photoreceptors, in addition being photoreceptors themselves, receive inputs from the classical photoreceptors (rods and cones) that in return affect the overall spectral sensitivity of the non-visual system as it changes with lighting conditions. Due to this time-varying spectral sensitivity and the relatively slow temporal processing, the relation between dynamic external light stimuli and the magnitude of non-visual responses cannot be explained with a single function or a simple threshold value. To better understand these non-linear and unknown relations, this thesis aims to develop a novel computational method, based on recent findings about the 'non-visual' - also called non-image-forming - effects of light on human health. A dynamic wavelength-dependent model framework is proposed to evaluate the non-visual health potential of light. This novel approach integrates the spectral effectiveness of irradiation and accommodates time-varying spectral sensitivity functions. These time series of light quantities serve as inputs for the light-driven model, which accounts for light intensity, duration, history, and timing of light exposure. By quantifying light in terms of spectral effectiveness and temporal dynamics, different light exposure patterns can be ranked in terms of its potential to have an impact on human health. The final objective of this thesis is to support the design of healthier buildings by applying evidence-based lighting criteria, which can then inform architectural design through a simulation-based approach. Incorporating non-visual effects into a building simulation workflow requires a good approximation of daylight spectra as it varies with sun position and sky type. Performance predictions must also account for occupant behavior and scheduling, which brings us to the question: How can we apply such a method to make informed decisions about our built environment? The integration of the proposed model into a functional simulation workflow is demonstrated using an architectural case study but first the non-visual spectral effectiveness of light will be evaluated under varying sky conditions to analyze the model output sensitivity to input accuracy. The model and its application to the built environment will then be investigated using multiple view directions and by considering occupant behavior and scheduling to make an immersive prediction within a space. This novel computational approach can be seen as a first step towards human-centric lighting application, simulating an occupant's light consumption to evaluate non-visual health potential that can support decision-making in the built environment.

EPFL2016

Modeling dynamic aspects of human nonvisual responses to light

María Lovísa Ámundadóttir, Marilyne Andersen, Steven W. Lockley

Since 2002, when the first reports on the discovery of a novel type of mammalian ocular photoreceptor were published, a new field of study at the intersection of photobiology and architecture started to emerge. These novel non-rod, non-cone photoreceptors in the retinal ganglion cell layer are the primary mediators of nonvisual responses to light in humans, including synchronizing circadian rhythms and directly alerting the brain. This study aims to understand how these nonvisual responses evolve over time with respect to changes in the intensity, spectral composition and exposure duration of light stimuli. The ultimate goal is to incorporate these effects of light into building design. Recent studies in the field of photobiology provide us with information about the human nonvisual responses to light. Researchers have identified intensity, spectrum, duration, history and timing of light exposure as important parameters that influence the responsiveness of the nonvisual system. Experimental research quickly reaches its limitations, because it is infeasible to carry out a complete experiment with respect to all parameter combinations. Mathematical models are the method of choice to enable such analysis. A block-structured model is proposed that combines linear filters, a nonlinear term and a feedback mechanism. The linear filters reflect the temporal processing between the light stimulus and the output response. The nonlinear term is the sigmoid-shaped intensity-response curve that receives input from the feedback mechanism to regulate the system’s response with changes in prior light history and timing of circadian phase. Moreover, the spectral sensitivity of the nonvisual system is modeled as a time-varying function. Based on this model, which takes the intensity, spectrum and duration of light exposure into account, it is possible to compare the nonvisual efficiency of different spectra as a function of duration. Results demonstrate that duration is an important parameter in addition to spectral sensitivity when comparing nonvisual effects of different light sources at low light intensities. This model provides a framework that can inform designers about the effects of lighting on human health and wellbeing in real-life settings. The ultimate goal of this work is not to reveal the underlying functionality of the retina, but rather to predict human nonvisual responses to light using mathematical models and test the predictions experimentally. Modeling dynamic aspects of nonvisual responses to light is important to understand the dynamic relationship between light and human nonvisual responses that occurs in real-world settings.

2013

Implications of the interplay between light and dark for human health in the built environment

María Lovísa Ámundadóttir, Marilyne Andersen

24-hour cycles of light and dark are one of the most significant factors in the built environment that affect human health and wellbeing. In addition to stimulating visual responses, light induces a range of circadian, physiological and behavioral responses in humans, including sleep quality, hormone production, alertness and cognitive performance. These nonvisual responses are primarily mediated via a novel type of photoreceptors that contain the photopigment melanopsin. These photoreceptors can function independently of the classical photoreceptors, rods and cones used for seeing, thus the human eye plays a dual role in detecting light. Since the overall purpose of lighting is to serve the needs of humans, the discovery of the melanopsin-containing photoreceptors should be addressed in architectural lighting design and engineering in buildings. The optimal daily doses of light and dark needed for synchronizing circadian rhythms or promoting other physiological and behavioral nonvisual responses are currently unknown, however there are evidences that light can have beneficial or harmful effects depending on the timing of the light exposure. Daytime light exposure can reduce sleepiness and improve performance but light exposure should be avoided at night, where it can suppress melatonin production resulting in circadian disruption. Human-centered approaches are rarely applied to evaluate building performance, where conventional recommendations for lighting are mainly based on the amount of brightness at a horizontal work plane. One of the challenges is to assess the amount of light received by occupants throughout the 24-hour day, whether the light source is daylight or electric. This paper summaries major implications of the interplay between light and dark for human nonvisual health in the built environment and discusses recent concepts that aim to integrate these findings into practice for supporting healthy lighting design.

2015