When was red light therapy first discovered?

The discovery of red light therapy, scientifically known as photobiomodulation (PBM), is a fascinating journey that spans over a century, blending accidental observations with rigorous scientific inquiry. While the therapeutic use of light dates back to ancient civilizations like Egypt and Greece, who used sunlight to treat various ailments, the specific discovery of red and near-infrared light’s biological effects is generally traced back to the late 19th and early 20th centuries.

The pivotal moment often cited is in 1893, when Danish physician Niels Ryberg Finsen began experimenting with light therapy. Although Finsen is most famous for using ultraviolet (UV) light to treat lupus vulgaris (for which he won the Nobel Prize in 1903), his work laid the foundational understanding that specific wavelengths of light could have profound biological effects. However, Finsen’s work focused largely on UV, which is destructive to bacteria but also damaging to human tissue in high doses. The specific benefits of the red spectrum were not fully isolated until later.

The true "discovery" of the low-level laser effect, which is the precursor to modern LED-based red light therapy, occurred somewhat accidentally in 1967. Endre Mester, a Hungarian physician, was conducting experiments to see if laser radiation could cause cancer in mice. He shaved the backs of mice and applied a low-power ruby laser to them. To his surprise, the laser did not cause cancer; instead, the hair on the treated mice grew back significantly faster and thicker than on the untreated control group. This serendipitous finding marked the birth of "Low-Level Laser Therapy" (LLLT). Mester realized that low-intensity light did not destroy tissue (like high-power surgical lasers) but rather stimulated cellular function.

Therefore, the discovery was a combination of intentional inquiry into light’s medical properties (Finsen) and an accidental observation of biostimulation (Mester). It took several decades for the scientific community to shift focus from the destructive power of light (surgery/UV sterilization) to its regenerative potential. The period between 1900 and 1960 saw scattered reports of red light improving wound healing, but it lacked a mechanistic explanation. It wasn't until Mester's 1967 experiment that the door opened for the systematic study of how non-thermal, low-energy red and near-infrared light could accelerate healing, reduce inflammation, and stimulate growth. This timeline highlights that while the concept of light therapy is ancient, the specific discovery of red light’s unique regenerative capabilities is a modern scientific achievement rooted in the mid-20th century.