How Light Affects Coat Growth

The duration of day-length and environmental temperature both change over the course of the year and regulate the length and density of a horse or pony’s coat in different seasons. Artificial lighting is often used to help optimise coat growth in our equine charges, to help with heat regulation when in training and visual aesthetics for the show ring.

Horses that have been exposed to a shortened winter daylength are responsive to long day light treatment in the spring to transition to a summer coat. This process can be brought forward by fitting an Equilume Light Mask. Using an Equilume light mask, a horse will completely shed out and produce a summer show coat in approx 6-8 weeks. Additional warmth in the form of blanketing will aid this process.

In order to prolong the summer coat, day length must be maintained at 16 hours of light and 8 hours of darkness, from the summer solstice onwards. There is a 1-month period after the summer solstice where extended day length can be applied in order to maintain a summer coat. Light masks should be fitted prior to Jan 21st  for Southern Hemisphere clients in order for the summer coat to be maintained.

Horses that have been exposed to the natural shortening of day length for more than a month after the summer solstice will start to transition to winter coat growth. Starting light treatment at this time will often be too late to reverse this transition, so they will need approximately 6 weeks ‘rest period’ to allow the winter coat to develop. After this, long-day light treatment can again be applied to begin the transition back to a summer coat.

Horses that have experienced a period of short autumn/winter days (6-8 weeks) and grow a heavier coat are responsive to artificial light treatment. After 6-8 weeks of a long-day photoperiod (16 hours of light, 8 hours of darkness) the coat will shed early to a summer coat. Additional warmth in the form of blanketing will aid this process.


The Cashel Light Mask is a rechargeable headpiece that provides the horse with biologically effective levels of blue light to:

  • maximise health
  • enhance coat condition
  • promote muscle development
  • positively influence mood, behaviour and overall well-being


It is a mobile light therapy device designed for both competition and leisure horses which can be used in the field, in the stable and when travelling.

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