In the late 1990’s, the Space Medicine Programme in the United States National Aeronautics and Space Administration (NASA), developed the LED which could have been used for therapeutic purposes. With the ability to mount multiple LEDs in planar arrays, large areas of tissue can be irradiated in one hands-off session, unlike the time-consuming and therapist-intensive punctal application with laser diodes. These arrays deliver almost laser-like wavelength specificity and with clinically useful penetration depths and intensities. In the past few years, LED-based systems have been successfully applied in an increasingly large number of therapeutic fields, and different wavelengths have emerged with a good photobiological basis and proven clinical utility. Each has its own specific cellular target or targets and biological action spectrum and reaction, but it has become even more clear that no single wavelength can accomplish everything and combination LED therapy has proved necessary for greatest efficacy. The application of LEDs has ushered in a new and exciting era in phototherapy, and offers a versatile therapeutic modality either as a stand-alone therapy, or as an adjunctive approach to enhance other therapeutic modalities.

The use of light sources for reducing pain and inflammation, augmenting tissue repair and regeneration, healing deeper tissues and nerves, and preventing tissue damage (among other medical applications) is known as low-level light therapy (LLLT), phototherapy, or photobiomodulation (PBM).

Basic therapeutic agent in phototherapy is photon energy and the modern accepted definition of phototherapy is:

“the use of low incident levels of photon energy at a particular wavelength, targeting tissue to achieve a clinically useful local or systemic effect, but without the creation of heat (athermal) or damage (atraumatic)”.

Phototherapy has definitely arrived in the clinical field for the treatment of pain, circulatory disorders, wound healing and skin rejuvenation. The new generation of LEDs has emerged as the main phototherapeutic modality used in treatment heads consisting of adjustable, hands-off planar arrays in systems which offer relatively inexpensive but effective therapy in all the above fields. The combination of one LED wavelength with another, used sequentially, has appeared  as  the  best and most effective approach. LED therapy may be used as a stand-alone light therapy, but has very interesting effects when used in an adjunctive manner to improve and speed up the already good results.

There is no doubt that LED phototherapy, when used based on the solid photobiological precepts of appropriate wavelength, target and photon intensity, is a safe, flexible, effective and comparatively inexpensive modality, very welcome in this era of ever-spiralling costs for both practitioners and patients.

Photobiomodulation (PBM)

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5215870/

Physical principles of Phototherapy

http://photobiology.info/Hamblin.html