Randomized trial of polychromatic blue-enriched light for circadian phase shifting, melatonin suppression, and alerting responses.
Level 2 - randomized trial
Individual randomized controlled trial in healthy volunteers
PubMed 30296404 · doi:10.1016/j.physbeh.2018.10.004
What was done
Twenty healthy participants were evaluated in a 7-day time-free environment protocol. Following two baseline days and a 26-hour constant routine (CR1) to establish initial circadian phase, participants were randomized to a 6.5-hour exposure during their biological night to either blue-enriched polychromatic light (17,000 K, n = 10) or standard white light (4000 K, n = 10) at equal photon density (1 × 10¹⁴ photons/cm²/s). Following recovery sleep, a second 30-hour constant routine (CR2) was conducted to measure melatonin suppression, dim light melatonin onset (DLMO) phase shifts, and subjective and objective alertness.
What was found
Blue-enriched light produced significantly greater melatonin suppression than standard light (mean ± SD: 70.9 ± 19.6% vs. 42.8 ± 29.1%, p < 0.05). Blue-enriched light also significantly improved subjective alertness (p < 0.05). However, there was no significant difference between the two light conditions in the magnitude of circadian phase delay shifts or in objective alertness measures.
Why it matters
The findings demonstrate that short-wavelength enrichment enhances acute neuroendocrine (melatonin suppression) and subjective alerting responses at identical photon flux, though these spectral differences may not necessarily translate into larger circadian phase shifts under these exposure parameters.
Limits
The sample size was very small (10 participants per arm), limiting statistical power to detect smaller differences in objective alertness or phase shifting. The study was conducted in healthy volunteers under strictly controlled laboratory conditions, which may not reflect real-world polychromatic lighting environments.
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