Red light wavelengths are the longest wavelengths in the visible light spectrum, ranging from 630nm to 700nm in length. The first studies in red light therapy were conducted by NASA. These experiments focused on the effects of red light on plants for the purpose of growing plants in space. They determined that red light promote plant growth and supported wound healing. The success of the NASA studies inspired further research to determine if red light therapy could benefit humans and results have shown that it offers substantial benefits with essentially no downside risk.
Red light is able to penetrate the outer layers of the skin and interact with living cells beneath. It works primarily by acting on the energy producing machinery of cells, known as the mitochondria, stimulating them to become more active and thereby generate more energy. Additionally, red light therapy benefits cells by bolstering their antioxidant and anti-inflammatory defense systems  and by activating genes that promote cell survival.
Cells exposed to red light create an abundance of energy that they can use to carry out basic functions as well as energy that they can use to increase their capacity to heal and repair themselves. This translates to longer-lived cells that are more productive and robust.
An area where red light therapy shows particular promise is in protecting visual health in older age. The retina, though a tiny structure, is continually active during waking hours. For this reason, its energy demands are high and to accommodate these demands the retina contains the highest concentration of mitochondria of any organ in the body. Loss of mitochondrial function is a key characteristic of the aging process, making the retina particularly susceptible to age-related decline.
Protects Retinal Cells
Recent human trials confirm the results of preliminary studies showing that red light therapy improves activity of retinal mitochondria and effectively slows the process of age-related vision loss[3,4].
Specifically, red light has been shown to selectively improve the function of visual cones, the cells of the retina that respond to color. With the aging process, cones gradually lose function, leading to loss of ability to distinguish shades of color clearly. Adding to the effect of the aging process on cones is that the fact that modern environments are controlled with artificial light so that humans tend to rely less on rods – the cells of the retina that respond in low light conditions. Loss of cone function combined with disuse and subsequent loss of rods leads to even greater loss of vision, particularly in low light conditions.
In a study published in the journal Nature, red light therapy restored cone function in older individuals by an average of 17%. In some instances, greater than 20% improvement was obtained. A similar clinical trial, published in The Journals of Gerontology, found that rod function improved, as well. Participants in both studies were exposed to red light in three-minute sessions and benefits from each session were observed to last for up to one week[3,4].
Reduces Retinal Inflammation
Another area where red light therapy may offer significant benefits for reducing age-related vision loss is by reducing inflammation of the retina. Inflammation initially affects the outer part of the retina where energy demand is the highest. Once it sets in, the immune response becomes activated and white blood cells flood the area, damaging retinal cells and causing vision loss. One study reported that in just five 90-second sessions of 670 nm red light therapy inflammation in the retinas of aged mice was significantly reduced.
Additionally, research is revealing that timing is essential for deriving benefits of red light therapy. Retinal mitochondria are more active in the morning and are most sensitive and receptive to red light therapy during that window. The Nature study, which included afternoon treatment sessions, found no effect from these sessions.
Scientists predict that red light therapy may hold great promise for preventing normal age-related vision loss and also as a potential treatment for retinal disease, such as macular degeneration.
Near-infrared light protect the photoreceptor from light-induced damage in rats. Advances in experimental medicine and biology, 2010. 664 https://www.ncbi.nlm.nih.gov/pubmed/20238037
Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. AIMS biophysics, 2017. 4(3) https://www.ncbi.nlm.nih.gov/pubmed/28748217
Weeklong improved colour contrasts sensitivity after single 670 nm exposures associated with enhanced mitochondrial function. Scientific Reports, 2021. 11(1): p. 1-9 https://www.nature.com/articles/s41598-021-02311-1
Optically Improved Mitochondrial Function Redeems Aged Human Visual Decline. The Journals of Gerontology: Series A, 2022. 75(9) https://academic.oup.com/biomedgerontology/article-pdf/75/9/e49/33753962/glaa155.pdf
Age-related retinal inflammation is reduced by 670 nm light via increased mitochondrial membrane potential. Neurobiology of aging, 2013. 34(2) https://www.ncbi.nlm.nih.gov/pubmed/22595370
- Aging retinal function is improved by near infrared light (670 nm) that is associated with corrected mitochondrial decline. Neurobiology of aging, 2017. 52 https://www.ncbi.nlm.nih.gov/pubmed/28129566