THE PHOTOBIOLOGICAL BASICS BEHIND LIGHT-EMITTING DIODE (LED) PHOTOTHERAPY

Phototherapy is, in its broadest sense, the use of light for any kind of surgical or nonsurgical treatment, but it is the athermal and atraumatic therapeutic application of light which is now accepted as the working definition of phototherapy. The early light-emitting diodes (LEDs) were unsuitable for clinical applica-tions because of low unstable output powers, broad wavebands and very high angles of divergence. In the late 1990’s, the Space Medicine Programme in the United States National Aeronautics and Space Admin-istration (NASA), developed the ‘NASA LED ’ with much higher output powers, a much narrower diver-gence and quasimonochromatic output. 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-inten-sive punctal application with laser diodes. These arrays deliver almost laser-like wavelength specificity and with clinically useful penetration depths and intensities, three of the most important considerations when considering cellular targets in the light of the first law of photobiology which states that without ab-sorption, there can be no reaction. In the past few years, LED-based systems have been successfully ap-plied in an increasingly large number of fields, and three major wavelengths have emerged with a good photobiological basis and proven clinical utility: blue, around 415 nm; red, around 633 nm, and near in-frared, around 830 nm. 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 and inexpensive therapeutic modality ei-ther as a stand-alone therapy, or as an adjunctive approach to enhance the good results of existing surgical modalities