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Non-image-forming effects of light: Implications for the design of living and working environments
Department of Architecture and Built Environment, Lund University, Sweden.ORCID iD: 0000-0003-0123-8996
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Seasonal variation in mood and subjective well-being are common at geographical locations further away from the equator. The 24-h light-dark cycle is the main time cue for synchronizing the human circadian clock to the external day and night.

Nowadays, people spend more of their waking day indoors, with less exposure to the natural daylight cycle, relying on artificial lighting which differs to daylight in a number of aspects, including intensity, spectral composition and light exposure pattern.

In parallel with the technology development that has been mainly driven by energy-saving reasons, it is important to investigate the non-image-forming effects of different properties of the daily and seasonal light exposure.

The overall aim of the thesis was to identify characteristics of the daily light exposure that are important to support physiological and psychological needs of humans. To achieve this objective a number of research questions were posed concerning daily and seasonal light exposure, seasonal variation in physiological processes and psychological parameters, and evaluation of light exposure with respect to non-image-forming effects. The research questions were investigated in a longitudinal research design with measurements conducted each month during the year at a high latitude with large seasonal variation in day lengths.

Self-report diaries and instruments for ambulatory- and static measurements were used to examine daily and seasonal light exposure in the working and living environments and for investigating the relationship between different parameters that can be used for evaluating light exposure according to non-image-forming effects of light. Seasonal variation in daily light exposure and regarding the pattern of light exposure was observed. Also, the results indicate a seasonal variation concerning the quality (i.e. spectral composition of the visible radiation) of the exposing light.

Two biological markers, melatonin and cortisol, were used for investigating seasonal variation in physiological processes relating to the circadian clock. The results showed higher morning melatonin concentrations and peak level of melatonin during the winter although no seasonal change was observed concerning the phase position of the melatonin rhythm.

Seasonal differences in mood and sleep-activity were studied by means of selfreport diaries and questionnaires. Seasonal variations were observed for both parameters. The results showed higher ratings of mood in the summer, particularly 6 in the evening, and a relationship between bedtime and evening light exposure and photoperiod length. Furthermore, longer sleep times was observed in the winter.

Appraisal of lighting conditions in the offices during the year was rated by the use of a questionnaire. The results showed some seasonal differences concerning the perceived qualities of the light and some associations between characteristics of the lit environments and positive affect were found.

Two methods, static- and ambulatory measurements, were used for recording lighting conditions in the working environments. Taken together, the results showed weak associations between the two methods.

Research have demonstrated an increased need for taking non-image-forming effects into consideration when designing working and living environments, especially at geographical locations with large variations in day length where people are exposed to much of the daily light exposure at the workplace. Laboratory research has provided a good understanding of the basic concepts. However, more field research is needed. Also, current research has demonstrated that new methods of measuring and evaluating lighting conditions are needed.

Place, publisher, year, edition, pages
Lund: Department of Architecture and Built Environment, Faculty of Engineering, Lund University , 2018. , p. 67
Keywords [en]
circadian rhythms, circannual, light exposure, melatonin, cortisol, sleep-wake behavior, perception, mood, spectral composition, measurement
National Category
Architectural Engineering
Identifiers
URN: urn:nbn:se:hj:diva-43220ISBN: 978-91-7740-112-4 (print)ISBN: 978-91-7740-113-1 (electronic)OAI: oai:DiVA.org:hj-43220DiVA, id: diva2:1292545
Opponent
Supervisors
Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-02-28Bibliographically approved
List of papers
1. Annual variation in daily light exposure and circadian change of melatonin and cortisol concentrations at a northern latitude with large seasonal differences in photoperiod length
Open this publication in new window or tab >>Annual variation in daily light exposure and circadian change of melatonin and cortisol concentrations at a northern latitude with large seasonal differences in photoperiod length
2016 (English)In: Journal of Physiological Anthropology, ISSN 1880-6791, E-ISSN 1880-6805, Vol. 36, no 1Article in journal (Refereed) Published
Abstract [en]

BACKGROUND: Seasonal variations in physiology and behavior have frequently been reported. Light is the major zeitgeber for synchronizing internal circadian rhythms with the external solar day. Non-image forming effects of light radiation, for example, phase resetting of the circadian rhythms, melatonin suppression, and acute alerting effects, depend on several characteristics of the light exposure including intensity, timing and duration, spectral composition and previous light exposure, or light history. The aim of the present study was to report on the natural pattern of diurnal and seasonal light exposure and to examine seasonal variations in the circadian change of melatonin and cortisol concentrations for a group of Swedish office workers.

METHODS: Fifteen subjects participated in a field study that was carried out in the south of Sweden. Ambulatory equipment was used for monthly measurements of the daily exposure to light radiation across the year. The measurements included illuminance and irradiance. The subjects collected saliva samples every 4 h during 1 day of the monthly measuring period.

RESULTS: The results showed that there were large seasonal differences in daily amount of light exposure across the year. Seasonal differences were observed during the time periods 04:00-08:00, 08:00-12:00, 12:00-16:00, 16:00-20:00, and 20:00-24:00. Moreover, there were seasonal differences regarding the exposure pattern. The subjects were to a larger extent exposed to light in the afternoon/evening in the summer. During the winter, spring, and autumn, the subjects received much of the daily light exposure in the morning and early afternoon. Regarding melatonin, a seasonal variation was observed with a larger peak level during the winter and higher levels in the morning at 07:00.

CONCLUSIONS: This study adds to the results from other naturalistic studies by reporting on the diurnal and seasonal light exposure patterns for a group living at a northern latitude of 56° N, with large annual variations in photoperiod length. It seems to be seasonal variation in the lighting conditions, both concerning intensities as well as regarding the pattern of the light exposure to which people living at high latitudes are exposed which may result in seasonal variation in the circadian profile of melatonin.

Keywords
Circannual, Cortisol, Light exposure, Melatonin, Northern latitude, Spectral composition, hydrocortisone, adult, circadian rhythm, female, human, male, metabolism, middle aged, photoperiodicity, physiology, season, sunlight, Sweden, time factor, Humans, Photoperiod, Seasons, Time Factors
National Category
Architectural Engineering
Identifiers
urn:nbn:se:hj:diva-43219 (URN)10.1186/s40101-016-0103-9 (DOI)000392974100001 ()27435153 (PubMedID)2-s2.0-85014606166 (Scopus ID)GOA JTH 2016; JTHBebyggdIS (Local ID)GOA JTH 2016; JTHBebyggdIS (Archive number)GOA JTH 2016; JTHBebyggdIS (OAI)
Available from: 2019-02-28 Created: 2019-02-28 Last updated: 2019-02-28Bibliographically approved
2. Seasonal variation in bright daylight exposure, mood and behavior among a group of office workers in Sweden
Open this publication in new window or tab >>Seasonal variation in bright daylight exposure, mood and behavior among a group of office workers in Sweden
2018 (English)In: Journal of Circadian Rhythms, ISSN 1740-3391, E-ISSN 1740-3391, Vol. 16, article id 2Article in journal (Refereed) Published
Abstract [en]

The purpose of the study was to investigate seasonal variation in mood and behavior among a group of office workers in Sweden (56°N). Thirty subjects participated in this longitudinal study. The subjects kept a weekly log that included questionnaires for ratings of psychological wellbeing and daily sleep-activity diaries where they also noted time spent outdoors. The lighting conditions in the offices were subjectively evaluated during one day, five times over the year. There was a seasonal variation in positive affect and in sleep-activity behavior. Across the year, there was a large variation in the total time spent outdoors in daylight. The subjects reported seasonal variation concerning the pleasantness, variation and strength of the light in the offices and regarding the visibility in the rooms. Finally, the subjects spent most of their time indoors, relying on artificial lighting, which demonstrates the importance of the lighting quality in indoor environments. 

Place, publisher, year, edition, pages
Ubiquity Press, 2018
Keywords
Circannual, High latitude, Light exposure, Lighting conditions, Psychological wellbeing, Sleep-wake behavior, adult, article, clinical article, female, human, human experiment, illumination, latitude, longitudinal study, male, mood, office worker, psychological well-being, questionnaire, seasonal variation, sleep, sunlight, Sweden, visibility
National Category
Occupational Health and Environmental Health Architectural Engineering
Identifiers
urn:nbn:se:hj:diva-41503 (URN)10.5334/jcr.153 (DOI)30210562 (PubMedID)2-s2.0-85051856248 (Scopus ID)JTHBebyggdIS (Local ID)JTHBebyggdIS (Archive number)JTHBebyggdIS (OAI)
Available from: 2018-09-19 Created: 2018-09-19 Last updated: 2019-02-28Bibliographically approved
3. Comparison of Static and Ambulatory Measurements of Illuminance and Spectral Composition That Can Be Used for Assessing Light Exposure in Real Working Environments
Open this publication in new window or tab >>Comparison of Static and Ambulatory Measurements of Illuminance and Spectral Composition That Can Be Used for Assessing Light Exposure in Real Working Environments
2019 (English)In: LEUKOS The Journal of the Illuminating Engineering Society of North America, ISSN 1550-2724, E-ISSN 1550-2716, Vol. 15, no 2-3, p. 181-194Article in journal (Refereed) Published
Abstract [en]

Reliable measurements are of utmost importance when investigating the relationship between light and human reactions. The aim of the present study was to compare two methods for measuring light exposure in real working environments. Ambulatory recordings of illuminance and irradiance were compared with static field measurements of horizontal illuminance at the normal working position, average horizontal illuminance in the room, vertical illuminance at the position of the eye in the normal angle of gaze, and spectral composition of the light radiation at the normal working position and at the position of the eye in the normal angle of gaze. The ambulatory measurements were carried out during a 3-day experimental period and were repeated monthly throughout the year. The static field measurements in the subjects’ offices were conducted five times during the year, in the morning and afternoon during one day. The relationship between the illuminances and irradiances measured with the portable instruments and the static measurements was statistically analyzed. Results from the analyses revealed that more than one third of the static measurements of vertical illuminances recorded were below 200 lx, and only 7% of the measurements exceeded 1000 lx. Measurements of the spectral composition of the light radiation in the rooms suggested that the light, although at a fairly low intensity, included relatively much radiation that can have a non-image forming effect. Furthermore, only a small number of significant correlations between the ambulatory and static measurements were found. Results from the t-tests showed that there were no differences between ambulatory measurements, and static measurements of horizontal illuminance at the normal position, average illuminance in the room and vertical illuminance at the position of the eye during three, five, and seven of the 10 measurements, respectively. There is a need to define appropriate parameters in order to describe the quality of a lit environment with respect to the non-image-forming effects of light radiation.

Place, publisher, year, edition, pages
Taylor & Francis, 2019
Keywords
Indoor lighting, measurement, nonvisual effects, Radiation effects, Ambulatory measurement, Indoor lightings, Non visuals, Portable instrument, Reliable measurement, Spectral composition, Static measurements, Working environment, Lighting
National Category
Architectural Engineering
Identifiers
urn:nbn:se:hj:diva-38822 (URN)10.1080/15502724.2017.1391101 (DOI)000472454300008 ()2-s2.0-85041096579 (Scopus ID)HOA JTH 2019;JTHByggnadsteknikIS (Local ID)HOA JTH 2019;JTHByggnadsteknikIS (Archive number)HOA JTH 2019;JTHByggnadsteknikIS (OAI)
Available from: 2018-02-13 Created: 2018-02-13 Last updated: 2019-08-19Bibliographically approved

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