Research

Hormonal

Exposure to blue-enriched light (peaking around 460 nm) during daytime hours acts as the strongest synchronizing agent for the human circadian rhythm by suppressing melatonin secretion, thereby enhancing alertness and cognitive performance.

Maximize exposure to bright, blue-enriched natural sunlight or high-quality artificial light during the morning and afternoon to anchor your circadian rhythm and boost daytime alertness. Conversely, minimize exposure to blue-emitting screens (phones, computers) in the 2-3 hours before bedtime to prevent melatonin suppression and sleep onset delays. Use night-mode filters on devices in the evening.

GoodSupportsHIGH confidence
Short wavelengths, perceived as blue color, are the strongest synchronizing agent for the circadian system that keeps most biological and psychological rhythms internally synchronized. ... Exposure to blue light during the day is important to suppress melatonin secretion... Blue wavelengths suppressed sleep-associated delta brainwaves better than green wavelengths and boosted the alpha wavelengths, which are related to alertness.
Siegfried Wahl et al. · Journal of Biophotonics · 2019

Why this rating

The paper is a review citing multiple experimental studies (e.g., [30], [31]) showing consistent spectral sensitivity peaks and melatonin suppression effects.

Source

The inner clock—Blue light sets the human rhythm

Siegfried Wahl et al. · Journal of Biophotonics · 2019

DOI 10.1002/jbio.201900102

narrative_reviewCited 272×
Read the paper
DOI resolved against Crossref · corpus check 2026-06-10

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