High‐intensity red light suppresses melatonin

640 nm monochromatic light at 1.1 x 10(17) photons/cm2 can acutely suppress melatonin levels in hamsters.

• Monochromatic light wavelengths above 600 nm are generally assumed to have little effect on neuroendocrine and circadian systems.
• Results indicate that exposure to 640 nm light can significantly lower melatonin production in hamsters.
• In normal healthy humans, 460 nm light exposure significantly suppressed melatonin, while 630 nm and 700 nm light caused minor reductions.
• Findings may relate to the functions of classical visual photoreceptors and newly identified retinal cells that respond to light for circadian regulation.
• The potential for red light to influence melatonin levels could inform practices in animal care and human lighting environments.

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