Assessment of the circadian stimulus potential of an integrative lighting system in an office area

Sammanfattning: Nowadays, people spend 90% of their time indoors, thus creating a healthy indoor environment for occupants is of great importance. Lighting in office spaces is an important aspect when it comes to occupant health and well-being. Research in the field of lighting has mostly been focusing on the visible light spectrum and image-forming (IF) processes. However, with the discovery of melanopsin containing intrinsically photosensitive Retinal Ganglion Cells (ipRGCs), non-visual effects of light such as circadian entrainment and alertness received more attention. Non-visual effects of light have previously been subject of research under laboratory conditions, yet, there are only few field studies that were conducted in office environments to evaluate these effects. The present study was undertaken to fill that gap by investigating an integrative lighting system in an office building, The Spark, at Medicon Village in Lund, Sweden. The study comprises of Technical Environment Assessments (TEAs) and Observed-based Environmental Assessments (OBEAs). TEAs include a series of photometric site measurements that were carried out for collecting information about the lighting system, calibration of the daylight model. Inputs used in simulations as well as sensor recordings were obtained by Movisens light and activity devices that were wrist-worn by the participants. OBEAs cover user assessment incorporating self-reported questionnaires and semi-structured interviews. Numerical modelling with the engine Radiance was used for photometric studies, and Adaptive Lighting for Alertness (ALFA) for circadian lighting potential. Lighting energy use of the building was calculated according to the standard EN 15193 since the building was completed in late 2019 and no full-cycle electricity bills were available at the time of the study. The results showed that the integrative lighting system can steer equivalent melanopic lux (EML), especially in areas with less daylight intake, therefore affecting the human circadian system. Based on the self-reported questionnaire and sensor recordings of wrist-worn devices, alertness of most participants increased with higher values of arbitrary unit (CCT·lux), that combines Correlated Color Temperature (CCT) and illuminance level detected by the devices. Circadian lighting simulations in ALFA showed higher EML values than the measured ones, while the closest values were obtained under only electric lighting. Semi-structured interviews indicated that most of the participants were positive towards the lighting system. The integrative lighting system complies with the energy benchmarks designated for existing and direct lighting systems; however, the system was designed with most attention to health and well-being of the occupants and to promote their circadian rhythms, rather than maximizing the energy-efficiency.