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Light is a form of energy that behaves like a wave and also as a stream of particles called photons. The development of monochromatic light sources with single or a narrow spectra of wavelengths paved the way for studies, which continue to show that appropriate doses and wavelengths of light are therapeutically beneficial in tissue repair and pain control. Evidence indicates that cells absorb photons and transform their energy into adenosine triphosphate (ATP), the form of energy that cells utilize. The resulting ATP is then used to power metabolic processes; synthesize DNA, RNA, proteins, enzymes, and other products needed to repair or regenerate cell components; foster mitosis or cell proliferation and restore homeostasis.

Other reported mechanisms of light-induced beneficial effects include modulation of prostaglandin levels, alteration of somatosensory evoked potential and nerve conduction velocity, and hyperemia of treated tissues. The resultant clinical benefits include pain relief in conditions such as carpal tunnel syndrome (CTS), bursitis, tendonitis, ankle sprain and temporomandibular joint (TMJ) dysfunction, shoulder and neck pain, arthritis, and post-herpetic neuralgia, as well as tissue repair in cases of diabetic ulcer, venous ulcer, bedsore, mouth ulcer, fractures, tendon rupture, ligamentous tear, torn cartilage, and nerve injury. Suggested contraindications include treatment of cancer; direct irradiation of the eye, the fetus, and the thyroid gland; and patients with idiopathic photophobia.

Each photon gyrates and bounces at a unique frequency and exhibits electrical and magnetic properties. As a result, their waves are called electromagnetic (EM) waves. Not all photons are visible to the human eye. What we see as light is only a minute range of the spectrum of EM waves associated with photons. The entire spectrum includes radio waves, infrared radiation, visible light, ultraviolet rays, x-rays, gamma rays, and cosmic radiation. The photons of different regions of the EM spectrum vibrate differently and have different amounts of energy.

Light for Therapy
Since the photons of different regions of the EM spectrum differ in energy and vibration frequency, they produce differing effects on humans. For example, gamma rays, x-rays, and UV rays tend to ionize matter and damage tissue because their photons have high energy. In comparison, radio waves have much lower energy and longer wavelengths, and are relatively innocuous. Infrared and visible light fall somewhere in between. The evidence shows that red and near infrared (NIR) light have therapeutic benefits; as a result, most of the equipment being sold today have either red, NIR, or a combination of red and NIR light.

Tissue Repair
Since Endre Mester, a Hungarian physician, first uncovered the therapeutic value of red light in the late 1960’s, different wavelengths of light have been shown to promote healing of skin, muscle, nerve, tendon, cartilage, bone, and dental and periodontal tissues. When healing appears to be impaired, these tissues respond positively to the appropriate doses of light, especially light that is within 600 to 1,000 nm wavelengths. The evidence suggests that low energy light speeds many stages of healing. It accelerates inflammation, promotes fibroblast proliferation, enhances chondroplasia, upregulates the synthesis of type I and type III procollagen mRNA, quickens bone repair and remodeling, fosters revascularization of wounds, and overall accelerates tissue repair in experimental and clinical models. The exact energy density (energy per unit area) necessary to optimize healing continues to be explored for each tissue.

Light, at appropriate doses and wavelengths, is absorbed by chromophores such as cytochrome c, porphyrins, flavins, and other light-absorbing entities within the mitochondria and cell membranes of cells. Once absorbed, the energy is stored as ATP, the form of energy that cells can use. A small amount of free radicals or reactive oxygen species â€" also known to be beneficial â€" is produced as a part of this process, and Ca++ and the enzymes of the respiratory chain play vital roles as well.

The ATP produced may be used to power metabolic processes; synthesize DNA, RNA, proteins, enzymes, and other biological materials needed to repair or regenerate cell and tissue components; foster mitosis or cell proliferation; and/or restore homeostasis. The result is that the absorbed energy is used to repair the tissue, reduce pain, and/or restore normalcy to an otherwise impaired biological process.

Works by other groups in Russia, Austria, Germany, Japan, Italy, Canada, and, more recently, Argentina, Israel, Brazil, Northern Ireland, Spain, the United Kingdom, and, of late, the United States, have produced a preponderance of evidence supporting the original findings of Friedrich Plog by showing that appropriate doses and wavelengths of low power light promote pain relief. More recent reports include studies that indicate that 77% to 91% of patients respond positively to light therapy when treated thrice weekly over a period of 4 to 5 weeks. Not surprisingly, CTS is one of the first conditions for which the FDA granted approval of low power light therapy.

Clinical Considerations
Light technology has come a long way since the innovative development of lasers more than 40 years ago. Other monochromatic light sources with narrow spectra and the same therapeutic values as lasers â€" if not better in some cases â€" are now available. These include light emitting diodes (LEDs) and superluminous diodes (SLDs). As the name suggests, SLDs are generally brighter than LEDs; they are increasingly becoming the light source of choice for manufacturers and researchers alike. The light source does not have to be a laser in order to have a therapeutic effect. It just has to be light of the right wavelength. Lasers, LEDs, SLDs, and other monochromatic light sources produce the same beneficial effects. Simply stated, light is light. The dose and wavelengths are critical. At present, it is believed that appropriate doses of 600 to 1,000 nm light promotes tissue repair and modulate pain.

Indications and Contraindications

Indications: The FDA has approved light therapy for the treatment of head and neck pain, as well as pain associated with CTS. In addition to these conditions, the literature indicates that light therapy may be beneficial in three general areas:

1. Inflammatory conditions (e.g., bursitis, tendonitis, arthritis, etc.)
2. Wound care and tissue repair (e.g.,Diabetic ulcers, venous ulcers, bedsores, mouth ulcers, fractures, tendon ruptures, ligamentous tear, torn cartilage, etc.)
3. Pain control (e.g., low back pain, neck pain, and pain associated with inflammatory conditions â€" carpal tunnel syndrome, arthritis, tennis elbow, golfer’s elbow, post-herpetic neuralgia, etc.)

Contraindications: There is a dearth of scientific evidence that light therapy, when used at appropriate doses, is contraindicated for any condition. However, experience and prudence suggest the following:

1. Cancer (tumors or cancerous areas)
2. Direct irradiation of eyes
3. Treatment of patients with idiopathic photophobia or abnormally high sensitivity to light.
4. Patients who have been pretreated with one or more photosensitivity enhancing agents, as for example, patients undergoing photodynamic therapy (PDT).
5. Direct irradiation over the fetus or the uterus during pregnancy.
6. Direct irradiation of the thyroid gland.
7. Over the epiphyseal plates of growing children.

Source: Enwemeka, Chukuka S., PT, PhD, FACSM. Rehab: interdisciplinary journal of rehabilitation. January/February 2004. Volume 17, Number 1.