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Specific light can affect life's rhythms

Research has proven that specific light can affect and regulate the Circadian Rhythm and Melatonin secretion.

Built-in Body Clocks

Research over the last decade has identified that specific light can affect and regulate the Circadian Rhythm and in turn Melatonin secretion and its effect on all mammals.

Often referred to as the "body clock," the Circadian Rhythm is the 24-hour cycle that tells our bodies when to sleep, rise, and eat - regulating many physiological processes.

Types of Light

Horselight delivers an optimized spectrum of light, at the right intensity to have a maximum effect on the Circadian Rhythm of the horse by regulating the secretion of Melatonin, also known as the sleep hormone.

Blue light within the short-wavelength blue light spectrum (465–485 nm) is the most effective at inhibiting Melatonin secretion, as Melanopsin production, its precursor is particularly sensitive to short wavelength, Blue Light.

Normal white LED or fluorescent lights do not deliver Blue Light at the level of intensity required to have any real effect on Melatonin suppression.


Key To Graphs:



Melatonin Suppression Curve




Red Light Function

Red light does not inhibit Melantonin secretion and hence the Circadian Rhythm. The HorseLight Advanced option will switch to red during the ‘off’ phase automatically by the controller, and thus will allow sufficient observational light at night without interfering with Melantonin secretion. This is useful for foaling as well as late arrival home from competition/ racing.

Red Light At Night In Detail

Exposure to White Light at night suppresses Melatonin production, impacts Circadian Rhythms and contributes to ill-health in humans. Human interaction with horses frequently occurs at night.

Studies have shown that dim Red Light would not suppress the nightly rise in Serum Melatonin levels in horses. In one study, six horses were maintained for consecutive 48 hour periods under a Light: Red (LR) and a Light: Dark (LD) photo-schedule. Transitions from light (>200lux, polychromatic white light) to red (5lux, peak wavelength 625nm) or dark (<0.5lux), and vice versa, coincided with ambient sunset and sunrise times.

Blood was collected at 2 hour intervals for 24 hours during each treatment via indwelling jugular catheters. Samples were harvested for serum and stored at -20°C until assayed for Melatonin by radioimmunoassay. Repeated measures two-way ANOVA and t-tests analysed for differences in LR and LD melatonin profiles and their circadian rhythm parameters. No time×treatment interaction or effect of treatment on serum melatonin levels were demonstrated (P>0.05). A robust main effect of time (P<0.0001) predominated, with melatonin levels rising at night under both treatments. Statistically significant differences were not observed when LR and LD were compared for circadian rhythm measures of night time peak, area under the curve (AUC), or for times of onset (evening rise), offset (morning decline), or peak duration. Low intensity red light at night did not impact the pattern of melatonin secretion in this study and is, therefore, unlikely to impact the physiology of circadian or seasonal regulation.

Source - Copyright © 2019 Elsevier Ltd. All rights reserved.

Red Light Spectrum Graph

Graph Key



Melatonin Suppression Curve

Circadian Sensitivity

Duration Of Light Exposure - The Natural Circadian Rhythm

In the northern hemisphere the daylight hours vary greatly between the summer months and the winter. For example in December we have 8 hours of daylight and 16 hours of darkness. March to September there is equal day and night (Equinox). June has the longest day (summer solstice).

Light Therapy

By setting back the equinox using artificial light we can alter the Circadian Rhythm and hence cycle brood mares early. This can be done through Light Therapy which is initiated 90 days before expected foaling date and maintained until the mare is again scanned in foal.

The relationship between coat shedding, day length and light intensity has been documented in several studies to date. One of the earlier ones was A&M University in Texas in the 1980's where they conducted a study comparing extended versus traditional day lengths for controlling coat lengths. In this study 16 yearlings and 2 year old mares and geldings were randomly assigned to natural day length or extended day length groups. The extended group received 16 hours of daylight per day and the non-extended group received natural daylight only. The study found that the coats of those horses exposed to extended daylight did not grow nearly as fast as those receiving normal daylight. We know that the coat maintenance is best achieved when Light Therapy is combined with using rugs to compensate for the winter coat.

In performance horses, Light Therapy should begin before mid July to maintain the summer coat into autumn. Similarly 8 weeks of light therapy is required to initiate shedding the coat earlier in the spring.

The Physiology Of Melatonin Control Using Specific Blue Light With Correct Lux And Duration

Light enters through the retina of the eye and suppresses the release of melatonin from the pineal glands, thus allowing the resumption of hormones to be released from the hypothalamus of the brain.

The Mechanism Of Melatonin

Melatonin is a pineal hormone produced during the hours of darkness, its pattern of secretion mimicking the light/dark patterns that occur during each 24 hour cycle. In breeding it acts as the daily decoder of seasonal changes in day length and regulates the circa-annual reproductive cycles of seasonally breeding mammals. The onset of the equine breeding season is triggered by increasing day length and concomitant reductions in Melatonin secretion.

The mechanism of Melatonin suppression has been well documented: light signals received by the retina and processed primarily by the photopigment melanopsin, located within the intrinsically photosensitive retinal ganglion cells, travel along the retino-hypothalmic tract to the hypothalamic suprachiasmatic nucleus. The suprachiasmatic nucleus is connected to the pineal gland via the superior cervical ganglia and photic signals inhibit the release of the neurotransmitter norepinephrine, which therefore fails to stimulate the synthesis of Melatonin.

During long days the inhibitory action of Melatonin on the mare’s reproductive axis is lifted. GnRH (gonadotropin releasing hormone) is released from the hypothalamus and stimulates the production of hormones which in turn stimulates the anterior pituitary to release follicle stimulating hormone and luteinising hormone, which act in concert to promote the growth, development and ovulation of ovarian follicles.

Mares generally require 60-90 days of photo stimulation before the first breeding cycle of the season. To achieve a foaling date closer to January 1st the mares' reproductive cycle must be tricked into resuming it earlier than is natural. This is done by artificial lighting.