###### Abstract  
Most people with dementia live at home supported by informal caregivers, but disturbed sleep patterns may induce a heavy burden of care. The beneficial effects of bright light on their sleep, health, and well-being have been demonstrated in clinical settings, but not in a home situation. We evaluated a dynamic lighting system in a real-life longitudinal single-case experimental design (SCED) with people with dementia living at home. Eleven people with dementia and their informal caregivers were included in this study with four 4-week periods of alternating exposure and none exposure in an introduction-withdrawal setup (ABAB). Objective light exposure data were collected and analyzed. The used study design seems applicable for this population and suitable for home use. Participant dropout did occur, but was due to health conditions rather than participant burden. The lighting system led to more light in the homes of the participants, as well as to higher actual individual light exposures, although the latter increased only moderately and not consistently across all participants, seasons, and times of day. The participants appreciated the lighting system even after 6 months. We reflect on individual differences, seasonal and daypart influences, and differential light effects. Recommendations and lessons learned are discussed. than people without dementia [9]. Spending significantly less time outside causes further understimulation of their biological clock, and this increases the risk of loss of healthy circadian entrainment [8; 9; 10; 11; 12]. Daylight naturally offers contrasting light and dark conditions over the 24 h day that our biological clock requires for healthy entrainment. The exact natural light dynamics are, of course, dependent on geographical location, time of day, and season. The illuminance and spectral composition of natural light are additionally influenced by weather conditions, such as haze and overcast [13; 14]. In addition, there are indications that, depending on the time of day and the individual's affective and/or mental state, different lighting conditions across the day are needed to optimally support human functioning [15; 16]. Particularly for persons who have older eyes, a diminished functioning of the internal clock, and who receive little direct exposure to daylight, dynamic artificial lighting that mimics the natural rhythm of night and day may stimulate physical and mental health and generate a positive experience. As the biological system is differentially sensitive to different wavelengths, dynamics in both light intensity and the light spectrum have an impact on physiological and psychological processes in the human body [17; 18]. In recent years, the use of dynamic lighting for people with dementia has become increasingly popular, and several care facilities have purchased dynamic lighting with the intention of improving the well-being and day-night rhythm of persons with dementia. However, these lighting systems are in most cases not suitable for people with dementia still living at home, mostly due to the purchase and installation costs and practical implications, such as actual usability and the personal preferences of people with dementia and their caregivers [10; 19]. Moreover, older adults best appreciate a lighting intensity level around 1000 lx, and due to age-related macular degeneration, their eyes are more sensitive to direct and, therefore, indirect light; thus lighting in which the light emitted by a source is diffusely reflected is often more appreciated [20; 21]. Standard light therapy boxes are therefore unsuitable for people with dementia as these offer direct light of very high intensity illuminance levels (lx) and, sometimes, of high correlated color temperature (CCT). Previous studies have demonstrated the beneficial effects of bright or dynamic light exposure on the sleep quality cognition and well-being of persons with dementia [22; 23; 24; 25]. Most studies on this subject have, however, been performed in nursing and care homes.