## 4 Discussion  
The aim of this longitudinal SCED study of three participants was to explore the possible influence of BDL on ADL for community-dwelling people with dementia and their informal caregivers. A study by [PERSON] et al. (2018) found positive effects of light on ADL in people with dementia in a group-care facility. We hypothesised that exposure to BDL could reduce ADL problems in community-dwelling people with dementia. This study  
Figure 9: (**a**) Scores washing; (**b**) Scores dressing; (**c**) Scores eating; (**d**) Scores visiting toilet; (**e**) Scores medication intake; (**f1–f5**) Scores Katz-ADL; Baseline = before start of the first phase; B1 = scores at the end of intervention phase one; A1 = scores at the end of placebo phase one; B2 = scores at the end of intervention phase two; A2 = scores at the end of placebo phase two; (**g1–g5**) Scores Lawton IADL; Baseline = before start of the first phase; B1 = scores at the end of intervention phase one; A1 = scores at the end of placebo phase one; B2 = scores at the end of intervention phase two; A2 = scores at the end of placebo phase two. found no statistically significant differences between BDL and placebo light with respect to ADL problems. However, other interesting results were found in this longitudinal SCED study. For example, qualitative results showed a stabilisation of ADL over a 5.5-month period with two participants. Because of the neurodegenerative nature of dementia, an increase in problems in ADL is expected without intervention, especially within six months [52]. Therefore, we hypothesised that the light protocol used in this study seems to be helpful to stabilise ADL performances, such as starting and performing activities, housekeeping, bathing and dressing for participant one and washing, dressing, medication intake, food preparation and housekeeping for participant two. Whereas participants one and two experienced more IADL problems, participant three experienced more BADL problems. Particularly in the last two phases, a deterioration in functioning can be seen for participant three in eating, toileting and medication intake. The deterioration in functioning is not reflected in the Katz and IADL, probably due to the fact the questionnaires are less specific and are administered only once per phase. Therefore, it is more useful to obtain a snapshot of the situation at that moment. From the literature, performance in toileting, transportation and feeding are intact in nearly all patients with mild dementia, with some deterioration reported for the later stages [53]. [PERSON] et al. [54] stated that bathing and dressing become more impaired with dementia progression. It could be that dementia is in a more severe stage in participant three as compared to the other two participants. For participant three, the course of ADL over a 5.5-month period is more erratic, which could mean that people earlier in their dementia process could have more benefits from light intervention compared to people in a more advanced stage. Earlier research in people with dementia or Parkinson's disease found a positive relation between bright light and ADL [25; 33]. Both studies used bright light with >1000 lux. In our study, there seems to be a trend that low-intensity light (~200 lux) and/or amber/red light could stabilise ADL decrease. Future research is necessary to investigate this finding more thoroughly. Another interesting finding is that our participants received significantly more light in the evening when they were exposed to amber light (in the intervention phases) and low-intensity light (in the placebo phases). [PERSON] and [PERSON] [55] stated in their review about lighting in the workplace that lighting levels at workplaces for human biological stimulation should be between 500 and 1000 lux. However, other research found evidence that a lower amount of lux (90-180 lux) can have an impact on alertness [56; 57]. Therefore, it could be that the placebo light of ~200 lux used in this study may already trigger some biological changes.