Effects of enhanced circadian lighting on well-being among older adults: pilot data from a 16-week placebo-controlled trial

• Enhanced CILS increased deep-sleep duration in older adults. • Enhanced CILS reduced nocturnal awakenings and breathing disturbances. • Working-memory accuracy and response speed improved with Enhanced CILS. • Self-reported fatigue and negativity trended lower with circadian lighting system. • Results support refining circadian lighting guidelines for aging populations. Circadian-effective indoor lighting may benefit sleep and cognition in older adults, yet most guidelines are based on younger populations. We conducted a randomized, cross-over field trial in an independent-living facility where older adults (n = 14; 79 ± 7 years; 73% female) experienced Static and standard circadian indoor lighting system (CILS) conditions in randomized order after a Baseline; after cross-over, all participants entered a single-arm extension with an Enhanced CILS schedule that intensified morning melanopic stimulus while keeping other procedures unchanged. Outcomes included objective sleep from an under-mattress sensor, weekly operation-span (O-Span) testing, and weekly surveys on sleep quality, depressive-related mood symptoms, and light comfort. Relative to Baseline and/or CILS, Enhanced CILS increased deep-sleep duration (128 ± 51 vs 81 ± 72 and 103 ± 55 min; p < 0.05) and percent deep sleep (32 ± 15% vs 20 ± 17%; p < 0.05), and reduced nighttime wakeups (3.25 ± 2.03 vs 4.56 ± 2.68; p < 0.05) and breathing disturbances (40 ± 34 vs 67 ± 54; p < 0.05). O-Span exact-order recall was highest under Enhanced CILS (85 ± 18%) compared with CILS (73 ± 22%) and Baseline (55 ± 23%; p < 0.05), with shorter response latencies; self-reported depressive-related feelings and fatigue also trended lower. In this real-world setting, enhanced circadian lighting improved sleep quality and working-memory performance beyond Baseline and, for several endpoints, beyond standard CILS, supporting tailored, higher-melanopic morning light with evening reduction for older adults and motivating confirmation in larger, season-balanced trials.