Light, entrainment and alertness: A case study in offices (original) (raw)
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Circadian-effective light and its impact on alertness in office workers
Lighting Research & Technology, 2018
A field study was conducted at two U.S. federal government office sites and two U.S. embassies to demonstrate whether circadian-effective lighting (providing circadian stimulus (CS) values of CS ≥ 0.3) could be installed in office buildings, and to determine whether this lighting intervention would reduce sleepiness and increase alertness, vitality and energy in office workers while at work. Desktop and/or overhead luminaires provided circadian-effective lighting at participants’ eyes during a two-day intervention. A pendant-mounted Daysimeter device was used to measure participant-specific CS values during the baseline and the intervention days. Participants also completed questionnaires inquiring about sleep habits, stress and subjective feelings of vitality and energy. The Daysimeter data showed that participants were exposed to significantly higher amounts of circadian-effective light while at work during the two intervention days compared to the baseline day. Self-reported slee...
Assessing Circadian Stimulus Potential of Lighting Systems in Office Buildings by Simulations
2019
Daylighting research has been primarily focused on the visible light spectrum for enhancing the quality and quantity of light in the built environment. Lighting design has been focusing on the reduction of glare and illuminance availability. A new assessment approach has been developed in recent years to address the non-visual effect of light such as circadian entrainment and alertness. The first objective of this study is to evaluate the glazing performance in terms of circadian stimulus potential, visual comfort, and task performance. The second objective is to evaluate the circadian stimulus potential of artificial lights. ALFA is used to measure the three glazing performance at eye-level in office spaces. Equivalent melanopic lux is measured at 1075 virtual nodes over 12 hours on March 21st. Results show that the electrochromic three zones system performs the best among the three glazing options.
Daylight in Office Buildings: Impact of Building Design on Personal Light Exposures, Sleep and Mood*
2015
Lighting design for office buildings has focused largely on the amount of light for visibility, strategies to reduce visual discomfort, and the use of daylight as a means to reduce energy in buildings. Little attention has been given to understanding how light affects occupants’ psychological and physiological systems, including circadian functions that regulate sleep, mood, and alertness. The specific goals of the present study were to: (1) perform photometric measurements at workstations in winter and late spring, and (2) analyze the impacts of personal light exposure on circadian entrainment using a wearable light and activity measurement device. Reported here are the results of the measurements performed during two seasons in a building located in the Northwest region of the United States.
Nocturnal white light exposure has shown marked results on subjective and objective indicators of alertness, vitality and mood, yet effects of white light during daytime and under usual office work conditions have not been investigated extensively. The current study employed a mixed-group design (N = 32), testing effects of two illuminance levels (200 lx or 1000 lx at eye level, 4000 K) during one hour of morning versus afternoon exposure. In four repeated blocks, subjective reports, objective performance and physiological arousal were measured. Results showed effects of illuminance on subjective alertness and vitality, sustained attention in tasks, and heart rate and heart rate variability. Participants felt less sleepy and more energetic in the high versus the low lighting condition, had shorter reaction times on the psychomotor vigilance task and increased physiological arousal. Effects of illuminance on the subjective measures, as well as those on heart rate were not dependent on time of day or duration of exposure. Performance effects were most pronounced in the morning sessions and towards the end of the one-hour exposure period. The effect on heart rate variability was also most pronounced at the end of the one-hour exposure. The results demonstrate that even under normal, i.e., neither sleep nor light deprived conditions, more intense light can improve feelings of alertness and vitality, as well as objective performance and physiological arousal.
How to Assess Alerting Effects of Daylight at the Workplace? Learnings from Semi-Controlled Studies
PROCEEDINGS OF the 29th Quadrennial Session of the CIE, 2019
Daylight, in which we evolved, is naturally rich in the blue component of the spectrum and has key properties when it comes to impacts on body functioning. Current lifestyles are driving the emergence of a 24-hour society that spends most of the time indoors (around 90%), where lighting conditions are a result of design and operation priorities derived from both comfort and energy criteria, which often lead to reduced access to daylight (smaller or shaded openings) to manage solar gains and glare risks. This may result in an insufficient (day)light exposure in daily life from a physiological perspective, light being an essential cue to properly entrain our internal circadian clock and increase subjective alertness. But it is still unclear whether it can have a significant beneficial effect when compared to artificial light from a psychophysiological standpoint. Most of the studies on acute alerting effects have been conducted in well-controlled laboratory settings, where somewhat extreme and narrowly defined lighting conditions have been tested. This paper proposes assessment and monitoring techniques that would apply to semi-controlled studies instead, and focuses on the impact of daylighting in work settings by exploring ways to investigate alertness neurobehaviour and physiology in realistic indoor conditions.
In this field study, we tested the effects of dynamic light scenarios and personal illuminance on visual experience, sleepiness, cognitive performance and sleep in an operational office. Two dynamic light scenarios, different in timing but with equal luminous exposure, were tested against a reference scenario in a counterbalanced crossover design. Frequent assessments of visual experience, alertness, performance and sleep showed that in both dynamic light scenarios visual comfort was slightly lower compared to the constant scenario. Additionally, sleepiness was lowest in the scenario with the brighter light timed around noon, whereas task performance and actual sleep were not significantly affected. The measured personal illuminance did not predict sleepiness and performance, yet variation and timing of these illuminances did positively relate to sleep onset and duration. When studying or implementing light scenarios aiming to deliver integrative lighting, the spatial and behavioral context should be considered as well.
Lighting Research & Technology, 2014
Lighting conditions in workplaces contribute to a variety of factors related to work satisfaction, productivity and well-being. We tested whether different photometric variables also influence visual perception and the comfort of the lighting, as well as subjective non-visual variables such as mood, alertness and well-being. Twenty-five young subjects spent two afternoons either under electric light or daylighting conditions (without view from the window). Subjects overall preferred the daylighting for visual acceptance and glare. Changes of photometric variables modulated changes in visual light perception, alertness and mood in the course of the afternoon. Finally, we found several associations of visual and non-visual functions, indicating a potential relationship of visual comfort with other circadian and wake-dependent functions in humans, which consequently could impact office lighting scenarios in the future.
Studying Response to Light in Offices: A Literature Review and Pilot Study
Buildings
Researchers have been exploring the influence of light on health in office settings for over two decades; however, a greater understanding of physiological responses and technology advancements are shifting the way researchers study the influence of light in realistic environments. New technologies paired with Ecological Momentary Assessments (EMAs) administered via smartphones provide ways to collect information about individual light exposure and occupant response throughout the day. The study aims to document occupant response to tunable lighting in a real office environment, including potential beneficial or adverse health and well-being effects. Twenty-three office employees agreed to participate in a twelve-week study examining occupant response to two lighting conditions (static vs. dynamic). No significant differences were observed for any of the measures, highlighting the importance and complexity of in-situ studies conducted in realistic environments. While prior office st...