Understanding Red Light Therapy Wavelengths in Horses

Red and near-infrared light therapy uses specific wavelengths of light to interact with biological tissues. In equine applications, 660nm, 850nm and 940nm wavelengths are studied for their different interactions with tissue and their potential roles in photobiomodulation. Understanding these differences helps horse owners make informed decisions about light therapy and the technology used in equine products.

660nm Red Light

At 660 nanometres (nm), light falls within the visible red portion of the spectrum. This wavelength is widely studied in photobiomodulation research, including investigations into how light interacts with cells and biological processes. Red light is generally absorbed and scattered differently from near-infrared light, influencing how it travels through tissue. Red light at 660nm is an important area of photobiomodulation research, with scientists investigating its interactions with cellular processes and its potential applications in equine care. Understanding how this wavelength interacts with tissue helps explain its role within red light therapy systems designed for horses.

How 660nm Red Light Interacts with Tissue

When red light reaches biological tissue, some of the light is absorbed by natural molecules within the tissue, while some is scattered or reflected. These interactions influence how much light remains available at different depths. Researchers studying photobiomodulation investigate how red light may interact with cellular photoacceptors, including molecules involved in mitochondrial energy processes. Cytochrome c oxidase, an enzyme involved in cellular respiration, has been proposed as one of the key photoacceptors, although its precise role and the mechanisms involved continue to be investigated. The response depends on more than wavelength alone, including the light dose, delivery method and characteristics of the target tissue.

What Research Tells Us About 660nm Red Light

Researchers have studied red light around 660nm to better understand how it interacts with living tissue and influences biological processes. Laboratory research has explored its effects on cells involved in tissue maintenance and repair, while veterinary research has investigated light therapy in animals. In horses, however, findings depend on the wavelength, light dose, treatment method and the condition being studied. For horse owners, the important takeaway is that 660nm is a well-studied red-light wavelength within photobiomodulation research, and understanding how it is delivered is just as important as knowing the wavelength itself.

850nm Near-Infrared Light

At 850nm, light falls within the near-infrared range and is invisible to the human eye. This wavelength is used in photobiomodulation research because its interaction with tissue differs from that of visible red light. Equine studies have investigated how near-infrared light travels through horse skin and underlying structures, highlighting the importance of skin characteristics, tissue thickness and the light source when considering how much light reaches a target area.

What Equine Research Tells Us

In a study using equine skin and flexor tendon samples, researchers compared light at 800nm and 970nm. They found that light transmission varied with skin and hair characteristics, skin preparation and wavelength. The study did not test 850nm directly, but its findings help explain why we cannot assume that every near-infrared wavelength behaves identically or reaches the same amount of tissue in every horse.

940nm Near-Infrared Light.

Near-infrared light at 940nm has different absorption characteristics from both 660nm red light and 850nm near-infrared light. One important difference is how water within biological tissue interacts with light at this wavelength. Water absorption increases as wavelengths approach the region around 970nm, which can influence how light travels through tissue. This means 940nm should not simply be described as a wavelength that always reaches deeper than 850nm. Its interaction with tissue depends on the wavelength, tissue composition and the way the light is delivered.

What Makes 940nm Different?

Why Combine 940nm with Other Wavelengths?

The 940nm wavelength has its own light-absorption characteristics, which is why it should be considered alongside other wavelengths rather than in isolation. When 940nm is combined with 850nm and 660nm, each wavelength brings different optical properties to the overall light profile.

ReGen Equine’s Tri-Wave Light System™: combines red and near-infrared wavelengths to provide a broader range of light interactions with tissue, rather than relying on a single wavelength alone.

The effectiveness of any light therapy approach depends on more than the number of wavelengths used. Wavelengths, dose, delivery method and application parameters all matter, and research continues to explore how these factors influence biological responses.

Wavelength Is Only Part of the Picture

Wavelength is an important part of understanding red and near-infrared light therapy, but it is not the only factor that influences how light interacts with tissue. The amount of light delivered, the distance and contact between the light source and the skin, the treatment area, and the duration of application can all affect light delivery.

Two products using the same wavelengths may not deliver light in the same way. Their LED configuration, output, design and application methods can differ, making it important to consider the overall system rather than wavelength specifications alone.

Understanding these factors provides a more complete picture of equine photobiomodulation and helps horse owners evaluate light therapy products more thoughtfully.

References

Quirk, B. J., & Whelan, H. T. (2020). What Lies at the Heart of Photobiomodulation: Light, Cytochrome C Oxidase, and Nitric Oxide—Review of the Evidence. Photobiomodulation, Photomedicine, and Laser Surgery, 38(9), 527–530. https://doi.org/10.1089/photob.2020.4905
Duesterdieck-Zellmer, K. F., Larson, M. K., Plant, T. K., Sundholm-Tepper, A., & Payton, M. E. (2016). Ex vivo penetration of low-level laser light through equine skin and flexor tendons. American Journal of Veterinary Research, 77(9), 991–999. https://doi.org/10.2460/ajvr.77.9.991
Michanek, P., Toth, T., Bergström, E., Treffenberg-Pettersson, H., & Bergh, A. (2021). Effect of infrared and red monochromatic light on equine wound healing. Equine Veterinary Journal, 53(1), 143–148. https://doi.org/10.1111/evj.13266
Mathioudaki, E., Rallis, M., Politopoulos, K., & Alexandratou, E. (2024). Photobiomodulation and Wound Healing: Low-Level Laser Therapy at 661 nm in a Scratch Assay Keratinocyte Model. Annals of Biomedical Engineering, 52, 376–385. https://doi.org/10.1007/s10439-023-03384-x
Lee, J.-M., & Kim, K.-H. (2019). An Experimental Study on the Penetration of 850nm and 940nm Infrared Radiation into Porcine Tissues. International Journal of Public Health and Clinical Sciences. https://doi.org/10.5958/0976-5506.2019.01217.8