Abstract Introduction Light plays a critical role in regulating circadian rhythms and supporting healthy sleep-wake cycles. These functions are especially important in older adults, who are more susceptible to sleep disturbances. However, much of the research on light and sleep in older adults has relied on short-term monitoring of light exposure or self-reports of time spent outdoors. Moreover, many of these studies quantified light using photopic measures rather than circadian-relevant, spectrally derived metrics, such as melanopic Equivalent Daylight Illuminance, which better quantify the non-visual effects of light. There is limited evidence regarding how long-term light exposure at home, given older adults’ lower mobility, relates to sleep outcomes. Methods We conducted a year-long observational study of 16 older adults (median age: 86 years) living alone in their homes. Spectral light sensors were installed in rooms where participants spent most of their time and were paired with passive infrared occupancy data to assess personal indoor light exposure throughout the day. Objective sleep data were collected using under-mattress sleep sensors. We examined light exposure patterns during daytime and evening hours, as well as time spent out of home, and evaluated their associations with sleep quality and duration. Results Participants spent a median of 2.4 hours per day out of the home, slept a median of 6.9 hours per night, had a median wake after sleep onset of 31 minutes, and a median sleeping heart rate of 59.7 bpm. Their personal light exposure at home featured low daytime and slightly elevated evening levels. While only weak relationships were observed, higher daytime and, unexpectedly, higher evening light exposures, as well as more time outside the home, were associated with better sleep outcomes. Further analyses are ongoing. Conclusion In this cohort of older adults living alone, indoor light exposure did not align with prevailing “bright-day, dark-evening” guidelines, which could contribute to circadian disruption and suboptimal sleep. Although all observed effects of light on sleep were weak, some were in line with current recommendations, while others were contrary to these, underscoring the need for further investigation into how everyday indoor light exposure affects sleep in older adults. Support (if any)
Vali et al. (2026) studied this question.