Débora Constantino

Low indoor light in urban housing can dis-rupt health and wellbeing, especially in older adultswho experience reduced light sensitivity and sleep/cir-cadian disruptions with natural aging. While controlledstudies suggest that enhancing indoor lighting mayalleviate the negative effects of reduced light sensitiv-ity, evidence for this to be effective in the real world islacking. This study investigates the effects of two lightconditions on actigraphic rest-activity rhythms and sub-jective sleep in healthy older adults (≥ 60 years) livingat home. Two photon-matched lights were compared; acontrol white light (4000 K) and a blue-enriched whitelight (17000 K) at two different intensities (300–450 lxand 1100–1200 lx respectively). Participants (n = 36, 25female) completed an 11-week randomized, cross-overstudy, comprising 1 week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 hin the evening), and 2 weeks of washout for each lightcondition. Participants completed sleep diaries, worea wrist actigraph and a light sensor necklace, and col-lected urine to measure 6-sulphatoxymelatonin. Longerduration of morning blue-enriched light significantlyimproved rest-activity rhythm stability and decreasedsleep fragmentation. More time spent above 2500 lxincreased actigraphy amplitude, daytime activity, andadvanced bedtime. Evening light exposure, however,increased sleep latency and lowered sleep efficiency.Our findings show morning blue-enriched light is ben-eficial whereas evening light should be avoided. Optimaltiming of self-administered light interventions thus mayoffer a promising strategy to improve sleep and rest-activity rhythms in older adults in real-world settings.