Débora Barroggi Constantino

Low indoor light in urban housing can dis-

rupt health and wellbeing, especially in older adults

who experience reduced light sensitivity and sleep/cir-

cadian disruptions with natural aging. While controlled

studies suggest that enhancing indoor lighting may

alleviate the negative effects of reduced light sensitiv-

ity, evidence for this to be effective in the real world is

lacking. This study investigates the effects of two light

conditions on actigraphic rest-activity rhythms and sub-

jective sleep in healthy older adults (≥ 60 years) living

at home. Two photon-matched lights were compared; a

control white light (4000 K) and a blue-enriched white

light (17000 K) at two different intensities (300–450 lx

and 1100–1200 lx respectively). Participants (n = 36, 25

female) completed an 11-week randomized, cross-over

study, comprising 1 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. Participants completed sleep diaries, wore

a wrist actigraph and a light sensor necklace, and col-

lected urine to measure 6-sulphatoxymelatonin. Longer

duration of morning blue-enriched light significantly

improved rest-activity rhythm stability and decreased

sleep fragmentation. More time spent above 2500 lx

increased actigraphy amplitude, daytime activity, and

advanced 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. Optimal

timing of self-administered light interventions thus may

offer a promising strategy to improve sleep and rest-

activity rhythms in older adults in real-world settings.