Human-centric lighting : circadian light knowledge, metrics and application

Humans now spend over 90% of their time indoors (EPA, 1989). This means that daily light exposure is at an all time low. There are serious health implications from the shift of evolutionary alignment with the rhythms of natural daylight to an interior environment that may have no connection to outdoor conditions. Circadian light is light that has an intended biological impact on the human circadian system. There is enough evidence that demonstrates the benefits of higher illuminance levels during key times of the day. Yet much of contemporary discourse has been focused on circadian light metrics without data on how meeting circadian light thresholds may affect occupant satisfaction and visual comfort. There is a gap between the scientific evidence and application strategies for designers and practitioners. This thesis examines the relationship between different circadian lighting design guidelines, the assessment organizations they come from, and the research they are based on. A significant inquiry into environmental assessment organizations is made that examines lighting related requirements and credits, as well as post occupancy evaluations of buildings and spaces. A simulation is performed to demonstrate the minimal decrease in energy use consumption from reduced illuminance levels. This along with occupant satisfaction data confirm that current interior lighting strategies do not provide overwhelming occupant satisfaction or significant energy reductions. This thesis makes the argument that circadian light should take on a larger role in the specification of luminaries and lighting design. A case is made for making knowledge of circadian lighting more accessible to designers and practitioners