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Light therapy may look simple, but there is real science behind the wavelengths.
Red and near-infrared light are used in a process known as photobiomodulation (PBM). Rather than heating tissue, PBM uses specific wavelengths of light to interact with biological processes inside cells. Research in veterinary medicine has explored its potential effects on cellular energy, inflammatory signaling, circulation, pain, and tissue recovery. A 2023 veterinary review from Washington State University describes red and near-infrared photobiomodulation as an increasingly used non-invasive modality in veterinary rehabilitation and sports medicine, while also noting that the strength of evidence varies by condition.
Blue light works differently. Rather than being used primarily for deeper photobiomodulation, wavelengths within approximately 400–470 nm have been studied for antimicrobial activity at the surface. Laboratory research has demonstrated effects against a range of bacteria and fungi, including organisms such as Staphylococcus aureus and Pseudomonas aeruginosa.
For horses, researchers are continuing to explore how these different wavelengths may fit into recovery, rehabilitation and everyday wellness.
What does the equine research actually show?
Here are several relevant peer-reviewed studies worth knowing:
- Light therapy and tendon + ligament injuries in performance horses
Researchers studied 26 performance horses with tendon or ligament injuries and compared rehabilitation alone with rehabilitation plus high-intensity light/laser therapy. The treated group showed statistically significant improvements in pain, swelling and lameness, as well as a greater reduction in the percentage of the tendon or ligament affected on ultrasound. The researchers concluded that light therapy could be useful as a supportive therapy for equine tendon and ligament injuries.
- Photobiomodulation and equine muscle function
Researchers from the University of Copenhagen and Writtle University College investigated photobiomodulation in the longissimus and gluteal muscles of horses. They found statistically significant changes in muscle-firing measurements following treatment, although the treatment did not significantly change mechanical pain-threshold measurements. The researchers concluded that the observed changes in muscle activity were consistent with changes associated with analgesia.
- Can therapeutic light actually penetrate equine skin?
Researchers at São Paulo State University studied light penetration through the skin of healthy Arabian and Quarter Horses. They confirmed that therapeutic light could penetrate equine skin and found that penetration varied based on the device and skin color. The study is important because effective photobiomodulation depends not simply on shining light at the horse, but on delivering an appropriate amount of light to the targeted tissue.
- Red light and equine wound healing
An experimental study involving eight horses evaluated 635 nm low-level laser therapy on full-thickness wounds. Researchers reported that the light-treated wounds healed faster than control wounds in that study.
However, wound-healing research is a good example of why wavelength, dose, and protocol matter. A later randomized, blinded study from the Swedish University of Agricultural Sciences tested approximately 637 nm red light plus 956 nm near-infrared light and did not find a clinically relevant improvement in experimental wound healing.
Read the Swedish University study on PubMed
- What does the broader veterinary evidence say?
A 2023 systematic review from the Swedish University of Agricultural Sciences evaluated 45 veterinary light-therapy studies, including numerous studies in horses. Researchers found some beneficial results, but also conflicting findings, variable treatment protocols, and limitations in study quality. Their conclusion was that photobiomodulation is scientifically interesting and widely used, but more standardized clinical research is still needed.
- Blue light at 470 nm and antimicrobial activity
Researchers with the USDA Agricultural Research Service specifically studied 470 nm blue LED light. They found that it inhibited bacterial and fungal growth under laboratory conditions, including effects on Pseudomonas aeruginosa.
Another study comparing 405 nm and 470 nm blue light found dose-dependent antimicrobial effects against P. aeruginosa and S. aureus, although susceptibility differed by organism and wavelength.
- What leading photomedicine researchers say about blue light
A major scientific review involving researchers from the Wellman Center for Photomedicine at Massachusetts General Hospital and Harvard Medical School evaluated antimicrobial blue light across the 400–470 nm spectrum. The review found substantial evidence that blue light can interact with naturally occurring photosensitive molecules within microorganisms, leading to the production of reactive oxygen species that can damage microbial cells. Research has demonstrated activity against bacteria and fungi, although effectiveness varies substantially based on wavelength, organism, and dose.
Read the Harvard/MGH review on PubMed
What does all of this mean for horses?
The simplest way to think about the science is that different wavelengths are being studied for different purposes.
Red light is primarily associated with photobiomodulation closer to the surface. Near-infrared light is particularly interesting for equine applications because longer wavelengths can penetrate more deeply into tissue. Equine studies have investigated photobiomodulation for muscles, tendons, ligaments, pain, and recovery, with several studies showing promising results.
Blue light is different. Research in the 400–470 nm range has demonstrated antimicrobial effects against bacteria and fungi in laboratory and other experimental models, making it particularly interesting for surface-focused applications. The scientific literature specifically supporting 470 nm blue light as an antimicrobial treatment in horses is still limited, however, so we believe it is more accurate to describe blue light as studied for its antimicrobial properties rather than as a proven treatment for equine infection.
The bottom line
Light therapy is not simply about making something glow red or blue. Wavelength, intensity, dose, treatment time, tissue depth, and the area being targeted all matter.
The scientific literature provides a strong biological rationale for photobiomodulation and a growing body of veterinary and equine research. Some equine studies have demonstrated meaningful improvements in measures related to tendon and ligament injuries, muscle function and tissue response, while others have found little or no benefit for particular applications.
That is why we view light therapy as a tool for supporting the horse's normal recovery and wellness routine — not a replacement for veterinary diagnosis or treatment.
And as the research continues to evolve, so will our understanding of how specific wavelengths can best be used to support the equine athlete.