Shine light on sleep: Morning bright light improves nocturnal sleep and next morning alertness among college students.
Level 2 - randomized trial
Controlled crossover trial in humans
PubMed 36058557 · doi:10.1111/jsr.13724
What was done
Twelve university students (mean age 24.92 ± 1.78 years) working in an office environment completed a baseline period (2 workdays) followed by two separate 5-workday interventions separated by a 1-week washout. Participants were exposed for 1.5 hours in the early morning to either bright electric light (1000 lx, 6500 K at eye level) or standard office light (300 lx, 4000 K). Sleep outcomes were assessed via actigraphy and sleep diaries. Subjective daytime sleepiness, mood, mental fatigue, perceived effort, and next-morning sleepiness were tracked daily.
What was found
Compared to standard office light, morning bright light resulted in significantly higher sleep efficiency (83.82% ± 1.60 vs. 80.35% ± 1.57, p = 0.02), a lower sleep fragmentation index (15.26% ± 1.31 vs. 17.18% ± 1.28, p = 0.05), and shorter time in bed (7.12 ± 0.13 vs. 7.51 ± 0.12 hours, p = 0.03). Compared to baseline, the morning bright light condition resulted in earlier sleep onset, shorter sleep latency, and lower next-morning sleepiness (p < 0.05), though other self-rated daytime outcomes (mood, mental fatigue, perceived effort, daytime sleepiness) showed no statistically significant differences (p > 0.05).
Why it matters
This study provides preliminary field evidence that altering indoor morning lighting parameters (intensity and color temperature) can modestly improve objective sleep quality and morning alertness in sedentary indoor workers.
Limits
The sample size was very small (n = 12), and the intervention duration was limited to 5 workdays per condition. The abstract does not specify whether the crossover sequence was randomized or blinded, and subjective daytime ratings mostly failed to show significant benefits.
Cited by
- supports Bright light exposure in the morning, especially from sunlight, increases daytime mood, focus, alertness, and improves sleep quality later that night.