A theoretical approach for therapeutic artificial supplementary lighting in elderly living spaces (vol 197, 107876, 2021)

Depression is a leading cause of disability and death worldwide. Due to physiological and psychological degeneration, the elderly suffer from an increased risk and incidence of depression. Light therapy (LT), a non intrusive approach for treating depression, exerts powerful effects on emotional and cognitive disorders, and can thus be installed in elderly living spaces (ELSs) in order to provide daily intervention that prevents the occurrence of the early phase of depression, delays its development, and promotes rehabilitation over its entire course. LT requires specific thresholds of light intensity, exposure duration, exposure time, and spectrum. The high incidence of seasonal affective disorder (SAD) triggered by daylight deprivation (caused by seasonal solar variation) suggests that daylight is insufficient for stable LT. Thus, custom-designed supplementary artificial lighting is needed.In this work, based on literature review and a synthesis of the light patterns related to antidepressant efficacy, visual comfort, and visual characteristics of the elderly, we recommended a set of a priori technical thresholds for light therapy installations in ELSs. Accordingly, using Radiance with Chengdu as a study case, we calculated the quantity and distribution of daylight and compared supplementary artificial lighting from the ceiling (horizontal lighting) and walls (vertical lighting), finding that vertical lighting is more advantageous in terms of both uniformity and energy efficiency for creating a lighting environment for daily light intervention in ELSs. This study introduces a theoretical approach for therapeutic lighting design, and the conclusions can provide technical guidance for applying light therapy in ELSs.