Sensitivity of the Human Circadian System to Short-Wavelength (420-nm) Light

A half-saturation constant of 2.74 x 10(11) photons/cm(2)/sec was identified for melatonin suppression by 420-nm light.

• Nine studies across rodents, monkeys, and humans indicate peak sensitivities to blue light in the range of 459 to 484 nm.
• A fluence-response relationship was established, showing that melatonin suppression increases with higher irradiances of 420-nm light.
• 460-nm light was found to be significantly more effective than 420-nm light in suppressing melatonin levels.
• The results provide insights into the short-wavelength sensitivity of human melatonin suppression, which could inform therapeutic light applications.

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