The effects of spectral tuning of evening ambient light on melatonin suppression, alertness and sleep.
Level 2 - randomized trial
Individual randomized crossover trial in humans.
PubMed 28472667 · doi:10.1016/j.physbeh.2017.05.002
What was done
Sixteen healthy participants (8 females) completed a 4-day inpatient, randomized crossover study evaluating bedroom-intensity light. Participants were exposed for 8 hours prior to a fixed bedtime to either blue-depleted circadian-sensitive LED light (C-LED) or standard fluorescent light (FL, 4100K) at equal illuminance (50 lux). Each exposure day was preceded 24 hours earlier by a dim light control condition (less than 3 lux). Investigators assessed melatonin suppression, subjective sleepiness, auditory reaction time, EEG spectral power, and polysomnographic sleep parameters including total sleep time, sleep efficiency, and slow-wave activity.
What was found
Compared to fluorescent light, blue-depleted LED exposure resulted in significantly less control-adjusted melatonin suppression (specific quantitative values not reported in the abstract). Subjective sleepiness showed no difference between lighting conditions, but auditory reaction times were significantly slower under C-LED 30 minutes prior to bedtime. EEG spectral power in the delta-theta bands (0.5 to 8.0 Hz) was significantly increased under C-LED compared to FL. Total sleep time, sleep efficiency, and slow-wave activity did not differ significantly between conditions, although a significant order effect was observed across these sleep parameters.
Why it matters
Depleting blue wavelengths from ambient evening light attenuates non-visual circadian disruption and promotes physiological pre-sleep de-arousal without requiring changes in illuminance level.
Limits
The sample size was very small (n=16) and restricted to healthy participants in an inpatient setting. The abstract reports no numerical effect sizes or confidence intervals for melatonin suppression or reaction times, and significant order effects complicated the sleep duration and architecture analyses.
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