Does artificial lighting benefit the conditioning of a horse?

By Paul Peacock

The claims of manufacturers of light therapy equipment for equines vary from the scientifically proven, through the scientifically dodgy to the downright bizarre. Trainers need to be able to sift through the advice and make financially viable judgements and weigh up the various proposed benefits against costs.

There is also the question of animal welfare to consider, comparing proposed benefits against the possible inconvenience of treatment. Certain forms of so-called light therapy, involving crystals and projected rainbows lie outside the remit of this article as much the same conclusions apply as in other forms of alternative treatment for equines.

However, there are many scientifically proven and highly practical uses for light therapy with thoroughbreds. Research by H. Kolárová, PhD, D. Ditrichová, MD, J. Wagner, PhD at three universities in the Czech Republic has conclusively shown that light penetrates skin tissues and there are a number of light receptors in the skin. These receptors have various functions including the production of more than one set of hormones and vitamins.

Mares at stud

Research in the USA showed that the day-length stimulated the pituitary gland to produce follicle stimulating hormone, thus bring the mare into season. This response is linked to the onset of spring, which in the natural world would bring the mare to foal at the appropriate time. However, this is not usually good enough to meet the cycle of yearling sales, especially in the US (much less so in Europe) and artificial light is used in the autumn and winter months to bring mares into season prematurely early. Up to 70 days of enhanced light, using medium intensity day-glo lighting, either in bulb or fluorescent form, is usually sufficient. More recent research has reduced this figure to les than a month with the use of the drug Sulpiride.

Implications of day length

Clearly, if the pituitary gland can be stimulated using artificial light, other benefits might be available to the horse if the onset of spring is artificially induced. These included increased energy, healthier immune system response, quicker and better recovery from injury and the vague yet important increased interest in life and work. This simple conclusion has led to a growing industry which in some cases uses pseudo science to market benefits that are simply not true.

The science

As far as it is currently understood, light has a number of effects under the skin, i.e. nothing to do with the eye. These effects are not fully understood, and consequently, in order to sell equipment, many companies resort to little understood, pseudo science in order to enhance the effects of light therapy equipment.
There are some compelling and intriguing reasons for looking in to light therapy, but there are not, as yet, any ‘double blind’ scientific studies to actually back up current claims.

Vitamin D

There are light receptors under the skin, but the production of this important vitamin does not need them. It is impossible for any mammal to get all its vitamin D from food sources. One of the many cholesterol molecules is broken down by a specific frequency of light to the vitamin. This only takes place under ultra violet B, and so ordinary bulbs and fluorescents do not produce the required frequency.
The effects of vitamin D deficiency used to be thought to be quite plain. However modern research has shown there to be a lot of problems directly or indirectly associated with lower amounts of the substance.
These can include depression, seasonal affective disorder, heart disease, rheumatoid arthritis, poor coat quality and other skin problems, periodontal disease and inflammatory bowel disease.
Consequently, Vitamin D being such an important molecule, the exposure of horses to an adequate amount of UVb light either in daylight or artificial form is important.

Endothelial light receptor cells

The science that might be at work in the other forms of light therapy shown by advertisers is detailed below, but these ideas are not particularly highlighted by many of the companies themselves. Usually you get the statement, “healing at the cellular level” or the “light heats up cells thus increasing their metabolism” or “the extra energy given to cells allows oxygen to become more available”. None of these statements can be attributed to factual evidence. However, current and possible areas for research include the following.
Horse skin, as in almost all mammals, contains a lot of light receptors. These use light to create a number of interesting effects.

First of all, nitric oxide synthatase (NOS), an enzyme which produces nitric oxide, is found more readily at higher light activity. This releases nitric oxide into the tissues which stimulates blood flow and has an effect on the nerves in the area. The interruption of morphine receptors can be initiated by nitric oxide, among other substances, thus providing an element of pain relief. In circumstantial evidence there does seem to be an increased immune system response directly associated to light receptors receiving extra incident light. This might be associated with oestrogens and their interaction with NOS, nitric oxide itself, and other as yet unknown substances.  In particular, wound repair and the healing of operation scars is becoming an interesting area of study which has been one of the favourite claims for using light therapy, particularly cold laser treatment.


Cold laser treatments are supplied in hand held form in a little box. You simply shine the light at the treatable area for a short while. A number of companies say that this treatment works by somehow transferring energy to and from ADP to ATP. This claim is nonsense. However, the non-science of the claims does not have to mean that the treatment doesn’t work. Hand held lasers are expensive, possibly out of the reach of many small yards. LED infra red diode therapy is where a string of infra red diodes are attached to the affected part. There are receptors in the skin which respond to infra red energy, normally to increase blood flow to remove the heat from the area. This can, therefore, have some benefit at the local level, but it is not conclusively shown. Furthermore many companies suggest using this equipment at the acupuncture points on the animal, causing the prospective user to weigh up the relative pros and cons of alternative therapies too, something beyond the scope of this article.

SAD adjustments, as described earlier, are possibly the best use of light therapy. It has to be said that the best and most cost effective light source is the sun, and stables need to be as light and airy as possible. However the simple use of daylight bulbs or fluorescents is sufficient to compensate for day length initiated disorders, keeping the animal in general good health. There are companies that sell booths with banks of lights on them. You can alternate these lights for infra red banks which create a warm radiance on the animal. They are frequently advertised with benefits such as shortening warm up / warm down times, and drying the animal after exercise or otherwise. Trainers will have to make up their own minds about these benefits.  There are no studies which detail the combined effect of heat and light on the health response of horses, yet common sense might provide some hints to their possible use.

Un-synchronised fluorescent lighting

Some horses. Like a small but significant number of humans, respond negatively to fluorescent lighting that is un-phased. Older, or cheap, fluorescent lights can have a flicker associated with them which can affect some thoroughbreds. Examples of crib biting and walking and kicking have been eased by simply changing the lighting.


There is plenty of anecdotal evidence that light therapy has some basic scientific truth about it. However the studies to completely show benefits are few and far between. Particularly, trainer will have to make up their own minds whether expensive equipment justifies the proposed benefits. Perhaps the very best light therapy can be obtained by simply changing the indoor lighting to daylight bulbs and the maintenance of a fourteen hour regime of daylight type radiation in the yard.