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      Good Places to Live and Sleep Well: A Literature Review about the Role of Architecture in Determining Non-Visual Effects of Light


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          Light plays a crucial role in affecting the melatonin secretion process, and consequently the sleep–wake cycle. Research has demonstrated that the main characteristics of lighting affecting the so-called circadian rhythms are spectrum, light levels, spatial pattern and temporal pattern (i.e., duration of exposure, timing and previous exposure history). Considering that today people spend most of their time in indoor environments, the light dose they receive strictly depends on the characteristics of the spaces where they live: location and orientation of the building, dimensions of the windows, presence of external obstructions, geometric characteristics of the space, optical properties of walls and furniture. Understanding the interaction mechanism between light and architecture is fundamental to design non-visually comfortable spaces. The goal of the paper is to deepen this complex issue. It is divided into two parts: a brief historical excursus about the relationship between lighting practice and architecture throughout the centuries and a review of the available research works about the topic. The analysis demonstrates that despite the efforts of the research, numerous open questions still remain, and they are mostly due to the lack of a shared and clear method to evaluate the effects of lighting on circadian rhythm regulation.

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          Dose-response relationship for light intensity and ocular and electroencephalographic correlates of human alertness.

          Light can elicit both circadian and acute physiological responses in humans. In a dose response protocol men and women were exposed to illuminances ranging from 3 to 9100 lux for 6.5 h during the early biological night after they had been exposed to <3 lux for several hours. Light exerted an acute alerting response as assessed by a reduction in the incidence of slow-eye movements, a reduction of EEG activity in the theta-alpha frequencies (power density in the 5-9 Hz range) as well as a reduction in self-reported sleepiness. This alerting response was positively correlated with the degree of melatonin suppression by light. In accordance with the dose response function for circadian resetting and melatonin suppression, the responses of all three indices of alertness to variations in illuminance were consistent with a logistic dose response curve. Half of the maximum alerting response to bright light of 9100 lux was obtained with room light of approximately 100 lux. This sensitivity to light indicates that variations in illuminance within the range of typical, ambient, room light (90-180 lux) can have a significant impact on subjective alertness and its electrophysiologic concomitants in humans during the early biological night.
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            Effect of Light on Human Circadian Physiology.

            The circadian system in animals and humans, being near but not exactly 24-hours in cycle length, must be reset on a daily basis in order to remain in synchrony with external environmental time. This process of entrainment is achieved in most mammals through regular exposure to light and darkness. In this chapter, we review the results of studies conducted in our laboratory and others over the past 25 years in which the effects of light on the human circadian timing system were investigated. These studies have revealed, how the timing, intensity, duration, and wavelength of light affect the human biological clock. Our most recent studies also demonstrate that there is much yet to learn about the effects of light on the human circadian timing system.
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              A phase response curve to single bright light pulses in human subjects.

              The circadian pacemaker is differentially sensitive to the resetting effects of retinal light exposure, depending upon the circadian phase at which the light exposure occurs. Previously reported human phase response curves (PRCs) to single bright light exposures have employed small sample sizes, and were often based on relatively imprecise estimates of circadian phase and phase resetting. In the present study, 21 healthy, entrained subjects underwent pre- and post-stimulus constant routines (CRs) in dim light (approximately 2-7 lx) with maintained wakefulness in a semi-recumbent posture. The 6.7 h bright light exposure stimulus consisted of alternating 6 min fixed gaze (approximately 10 000 lx) and free gaze (approximately 5000-9000 lx) exposures. Light exposures were scheduled across the circadian cycle in different subjects so as to derive a PRC. Plasma melatonin was used to determine the phase of the onset, offset, and midpoint of the melatonin profiles during the CRs. Phase shifts were calculated as the difference in phase between the pre- and post-stimulus CRs. The resultant PRC of the midpoint of the melatonin rhythm revealed a characteristic type 1 PRC with a significant peak-to-trough amplitude of 5.02 h. Phase delays occurred when the light stimulus was centred prior to the critical phase at the core body temperature minimum, phase advances occurred when the light stimulus was centred after the critical phase, and no phase shift occurred at the critical phase. During the subjective day, no prolonged 'dead zone' of photic insensitivity was apparent. Phase shifts derived using the melatonin onsets showed larger magnitudes than those derived from the melatonin offsets. These data provide a comprehensive characterization of the human PRC under highly controlled laboratory conditions.

                Author and article information

                Int J Environ Res Public Health
                Int J Environ Res Public Health
                International Journal of Environmental Research and Public Health
                23 January 2021
                February 2021
                : 18
                : 3
                : 1002
                Department of industrial Engineering, University of Naples Federico II, Piazzale Tecchio, 80, 80125 Naples, Italy; francesca.fragliasso@ 123456unina.it
                Author notes
                [* ]Correspondence: bellia@ 123456unina.it
                Author information
                © 2021 by the authors.

                Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license ( http://creativecommons.org/licenses/by/4.0/).

                : 23 December 2020
                : 20 January 2021

                Public health
                architecture and lighting,circadian lighting,daylight,integrative lighting,literature review,non-visual effects of light


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