A double-blind randomised controlled crossover trial of the effect of blue-enriched ambient light on sleep in older adults with sleep disturbance: the CleverLights study

Light interventions have been investigated for treating sleep disturbances in older adults; however, findings are mixed. This proof-of-concept trial investigated the effect of blue-enriched ambient light on electroencephalographic (EEG) sleep in older adults with self-reported poor sleep. Twelve participants (65.6 ± 8.7 years) were randomly exposed to two 72-h in-laboratory light conditions separated by 2 weeks. During the day, participants were exposed to either blue-enriched light (intervention: melanopic equivalent daylight illuminance (EDI) = 843.6 lx) or standard light (control: melanopic EDI = 215.8 lx). Three hours before habitual bedtime, illuminance was reduced, with greater blue light attenuation in the intervention (melanopic EDI = 49.5 lx) than control (melanopic EDI = 60.8 lx). On the third night, high-density EEG sleep, cognitive performance and body temperature were assessed. The primary outcome was wake-after-sleep-onset (WASO). Secondary outcomes included polysomnography-derived sleep parameters, sleep spindles, cognitive performance and body temperature. High-density EEG spectral power analyses were exploratory. There was no significant difference in WASO (136.1 ± 52.6 min vs. 117.2 ± 43.9 min; p = 0.338) between intervention and control. Intervention light significantly increased sigma activity (12-16 Hz) during N1 (p = 0.010) and N2 (p = 0.017) sleep. The distal-proximal skin temperature gradient (surrogate of peripheral heat dissipation) before and after lights out increased under intervention compared to control (-1.21°C ± 1.44°C vs. -1.85°C ± 1.39°C, p < 0.001). Daytime enrichment and evening depletion of blue light did not improve objective sleep outcomes in older people with sleep disturbance, but exploratory analyses showed increased sigma activity during sleep. Lighting interventions to improve sleep in older populations require further investigation. Trial Registration: ACTRN12619000138189.