Human melatonin rhythms are highly sensitive to resetting by blue light

Exposure to 6.5 hours of monochromatic light at 460 nm induces a two-fold greater phase delay in the circadian rhythm compared to 555 nm light.

• The resetting response of the human circadian pacemaker is influenced by light wavelength.
• 460 nm monochromatic light suppresses melatonin levels twice as much as 555 nm light of equal intensity.
• The effectiveness of light in adjusting circadian rhythms is affected by the duration of exposure as well as the wavelength.
• The human circadian system is most sensitive to shorter wavelengths of light, specifically in the blue spectrum.
• Standard measurements of light (photopic lux) may not accurately reflect the photic influence on the circadian pacemaker.

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