Red light at night permits the nocturnal rise of melatonin production in horses.

•Low intensity red light at night permits the nocturnal rise in serum melatonin in horses.•Similar 24-h melatonin production patterns were observed in horses maintained under darkness or red light at night.•Red light at night permits visibility and is an alternative to white light to avoid circadian rhythm disruption in horses.•Nocturnal red light use in equine stabling may provide important health benefits for horses.