Population Based Lighting Study on Older Adults

Pittsburgh Sleep Quality Index (PSQI) ranges from 0 (better) to 21 (worse). A score <= 5 is associated with good sleep quality, while a score > 5 is associated with poor sleep quality. A higher PSQI score indicates poorer sleep quality, therefore the hypothesis to be tested is that a participant's sleep quality will improve (i.e. PSQI score will decrease) at the end of the light intervention period compared to baseline. Hence, a negative PSQI difference between baseline and follow-up indicates an improvement in sleep quality.

Change in mental and physical health as measured by Euroqol 5D difference between the baseline and the end of the light intervention period. The Euroqol 5D measures the perceived quality of life and ranges from - 0.57 (worst perceived quality of life) to 1 (best health state). A positive difference from baseline to the end of the follow-up period indicates an improvement in the quality of life.

Change in Interdaily Stability (IS), as derived from wrist actigraph, between the baseline and the end of the light intervention period.

Interdaily Stability (IS) is an index that estimates the stability of the 24-hour rest-activity rhythm across days, quantifying how consistent individual's daily pattern is over time. It ranges from 0 (absence of a stable rhythm) to 1 (perfectly stable rhythm). The hypothesis to be tested is that a participant's IS will increase at the end of the light intervention period compared to baseline; hence, a positive difference between baseline and follow-up indicates an improved rest-activity rhythm.

Change in Intradaily Variability (IV), as derived from wrist actigraphy, between the baseline and the end of the light intervention period.

Intradaily Variability (IV) is an index that reflects fragmentation of the 24-hour rest-activity rhythm within a day, based on the frequency of transitions between rest and activity. It ranges from 0 to 1, with higher values indicating more fragmented rhythms. The hypothesis to be tested is that a participant's IV will decrease at the end of the light intervention period compared to baseline; hence, a negative difference between baseline and follow-up indicates an improved rest-activity rhythm.

Change in Relative amplitude (RA), as derived from wrist actigraphy, between the baseline and the end of the light intervention period.

Relative Amplitude (RA) measures the strength of the 24-hour rhythm: (M10-L5)/(M10+L5). M10 is the mean activity during the 10 most active consecutive hours, and L5 during the 5 least active hours. RA ranges from 0 to 1 and reflects the normalized difference between the most active and least active periods of the day: higher values indicate a well-defined rhythm, lower values a weaker or disrupted rhythm. The hypothesis to be tested is that a participant's RA will increase at the end of the light intervention period compared to baseline; hence, a positive difference between baseline and follow-up indicates an improved rest-activity rhythm.