Red light at night permits the nocturnal rise of melatonin production in horses.
Authors: Murphy B A, O'Brien C, Elliott J A
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Red Light and Equine Melatonin Production Nocturnal light exposure suppresses melatonin in humans with documented consequences for circadian health, yet stable management and veterinary procedures frequently require nighttime illumination around horses. Murphy and colleagues investigated whether dim red light (5 lux, 625 nm wavelength) would preserve the normal nocturnal melatonin surge, comparing it against complete darkness using a crossover design in six horses with 2-hourly blood sampling over 24-hour periods. Red light conditions produced indistinguishable melatonin profiles compared to darkness: no differences emerged in peak nocturnal levels, area under the curve, onset timing, offset timing, or peak duration (P>0.05), whilst a robust circadian effect predominated across both treatments (P<0.0001). For equine practitioners, this finding suggests that task lighting using low-intensity red wavelengths during night-time stable work, veterinary procedures, or foaling attendance would not compromise melatonin physiology or disrupt circadian and seasonal endocrine regulation—a practical reassurance for situations where complete darkness is incompatible with safe, effective care. The work aligns with photobiology principles but specifically validates red-light implementation in equine settings where human safety and animal welfare must both be prioritised.
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Practical Takeaways
- •Dim red light can be safely used for nighttime work with horses without disrupting their melatonin production and circadian rhythms, unlike white light
- •If night work is necessary, switching from white to red lighting (around 5 lux) may help preserve horses' natural circadian physiology and associated health benefits
- •This finding supports use of red lighting in stable management during night hours as a welfare-friendly alternative to white light
Key Findings
- •Dim red light (5 lux, 625nm wavelength) did not suppress nocturnal melatonin rise in horses compared to dark conditions
- •Melatonin levels showed robust time-dependent elevation at night under both red light and dark treatments (P<0.0001)
- •No statistically significant differences were found between red light and dark conditions for circadian rhythm parameters including peak timing, area under curve, onset, offset, or peak duration
- •Low-intensity red light at night is unlikely to disrupt circadian or seasonal regulation physiology in horses