The bright and dark side of blue-enriched light on sleep and activity in older adults

Indoor light levels in urban housing are often low, potentially disrupting sleep and circadian rhythms. This is particularly important for older adults as advancing age is accompanied by physiological changes that reduce the amount of light reaching the retina, such as increased lens density, reduced pupil size, and diminished number of photoreceptors. These alterations manifest in disturbances to sleep and circadian rhythms, frequently observed in older adults. However, studies indicate that improving indoor light conditions can alleviate age-related sleep and circadian disturbances. In our study, we wanted to investigate the effects of two photon-matched light conditions on actigraphic rest-activity rhythms and subjective sleep in healthy older adults (≥ 60 years) living at home.

We recruited 36 participants (25 female) with sleep problems who completed an 11-week randomised, cross-over study comprising one week of baseline, 3 weeks of self-administered light exposure (2 h in the morning and 2 h in the evening), and 2 weeks of washout for each light condition. Each participant was exposed to two light sources; a control white light (4000 K) and a blue-enriched white light (17000 K) at two different intensities (300-450 lux; 201- 311 melanopic EDI and 1100-1200 lux; 773 – 1591 melanopic EDI respectively). Participants completed sleep diaries, wore a wrist actigraph and a light sensor necklace.

We found that morning blue-enriched light exposure significantly improved the stability of rest/activity rhythms and decreased sleep fragmentation. The amount of light exposure also produced significant effects, with more time spent above 2500 lux being associated with higher activity amplitude, more daytime activity, and earlier bedtime. Evening light exposure, however, increased sleep latency and decreased sleep efficiency.

These findings have shown that timed, self-administered light exposure in the home environment has measurable positive effects on several parameters of sleep and activity. Specifically, they show that morning blue-enriched light is beneficial whereas evening light should be avoided. Despite real-world variability, our data provide evidence of light’s supplementation effects outside controlled settings, supporting strategies to improve sleep and reduce healthcare costs in ageing populations.