Blue-Enriched Morning Light as a Countermeasure to Light at the Wrong Time: Effects on Cognition, Sleepiness, Sleep, and Circadian Phase.
Level 2 - randomized trial
Small within- and between-subject controlled experimental trial in humans
PubMed 28637029 · doi:10.1159/000477093
What was done
Eighteen young participants completed a seminaturalistic, within- and between-subject experimental study. Participants were exposed to 2 morning lighting regimens (mixed blue-enriched light vs. control light for 3 days each), followed by 3 evening lighting conditions (blue-enriched, bright orange, or dim light). Investigators assessed subjective sleepiness, reaction times, salivary melatonin concentrations, circadian phase shifts, and nighttime sleep parameters.
What was found
Blue-enriched morning lighting acutely reduced sleepiness and led to faster reaction times compared to control lighting, with some benefits persisting into the evening and performance improving over consecutive days. The magnitude of evening-light-induced circadian phase shifts was significantly smaller following blue-enriched morning light exposure. Additionally, nighttime total sleep time was longer following orange evening light compared to blue evening light. The abstract did not report numerical values, effect sizes, or confidence intervals.
Why it matters
This study provides experimental evidence that optimizing daytime light spectrum and intensity can buffer the circadian system against the disrupting effects of artificial light in the evening.
Limits
The study had a very small sample size (n = 18) restricted to young healthy individuals. Exact numerical results, baseline values, and statistical intervals were omitted from the abstract. Long-term clinical and health outcomes outside a seminaturalistic short-term protocol remain unmeasured.