Light therapy has been proven in over 40 years of independent research worldwide to deliver powerful therapeutic benefits to living tissues and organisms. Both visible red and infrared light have been shown to effect at least 24 different positive changes at a cellular level. Visible red light, at a wavelength of 660 nanometers (nm – 1 nanometer is equal to one billionth of a meter), penetrates tissue to a depth of about 8-10mm. This lower strength light is very beneficial in treating problems close to the surface such as wounds, cuts, scars, trigger and acupuncture points, and is particularly effective in treating infections. Infrared light (904nm) penetrates to a depth of about 30-40mm which makes it more effective for treating ailments of bones, joints, and deep muscle tissue.
The diverse tissue and cell types in the body all have their own unique light absorption characteristics; that is, they will only absorb light at specific wavelengths and not at others. For example, skin layers, because of their high blood and water content, absorb red light very readily, while calcium and phosphorus absorb light of a different wavelength. Although both red and infrared wavelengths penetrate to different depths and affect tissues differently, their therapeutic effects are similar.
Research has shown no adverse side effects from this form of therapy. Occasionally, one may experience an increase in pain or discomfort for a short period of time after treating chronic conditions. This occurs as the body reestablishes new equilibrium points following treatment. It is a phenomenon that may occur as part of the normal process of recovery.
Light therapy has also been given the name “phototherapy”. A study done by the Mayo Clinic in 1989 suggests that the results of light therapy are a direct effect of light itself, generated at specific wavelengths, and are not necessarily a function of the characteristics of coherency and polarization associated with lasers. In a study entitled Low-Energy Laser Therapy: Controversies and New Research Findings, Jeffrey R. Basford, M.D. of the Mayo Clinic’s Department of Physical Medicine and Rehabilitation, suggests that the coherent aspect of laser may not be the source of its therapeutic effect. He states “firstly, the stimulating effects (from therapeutic light) are reported following irradiation with non-laser sources and secondly, tissue scattering, as well as fiber optic delivery systems used in many experiments rapidly degrade coherency . . . Thus any effects produced by low-energy lasers may be due to the effects of light in general and not to the unique properties of lasers. This view is not difficult to accept when it is remembered that wave-length dependent photobiochemical reactions occur throughout nature and are involved in such things as vision, photosynthesis, tanning and Vitamin D metabolism. In this view, laser therapy is really a form of light therapy, and lasers are important in that they are convenient sources of intense light at wavelengths that stimulate specific physiological functions.” (Lasers in Surgery and Medicine 9:1-5, Mayo Clinic, Rochester, Minnesota, 1989).
LED’s and LASERS are no more than convenient devices for producing electromagnetic radiation at specific wavelengths. Other studies establish that it is the light itself at specific wavelengths that is therapeutic in nature and not the machine which produced it. For example, Kendric C. Smith at the Department of Radiation Oncology, Stanford University School of Medicine, concludes in an important article entitled The Photobiological Effect of Low Level Laser Radiation Therapy (Laser Therapy, Vol. 3, No. 1, Jan – Mar 1991) that “1) Lasers are just convenient machines that produce radiation. 2) It is the radiation that produces the photobiological and/or photophysical effects and therapeutic gains, not the machines. 3) Radiation must be absorbed to produce a chemical or physical change, which results in a biological response.”
The equation between the machine and the biological response is a common error often made by those who wish to promote the commercial interests of low-energy laser technology. Light radiation must be absorbed to produce a biological response. All biological systems have a unique absorption spectrum which determines what wavelengths of radiation will be absorbed to produce a given therapeutic effect. The visible red and infrared portions of the spectrum have been shown to have highly absorbent and unique therapeutic effects in living tissues.
The following are definitions of commonly used terms used in connection with the use of therapeutic light devices:
- Visible Light: light that is within the visible spectrum, 400nm(violet) to 700nm(red)
- Infrared Light: light in the invisible spectrum below red, from 700nm to 2,000nm
- Frequency: number of cycles per second measured in Hertz
- Coherency: wavelengths of light traveling in phase with one another
- Monochromaticity: light that is of one color, or one wavelength
- Collimation: light focused in a beam, maintaining a constant diameter regardless of its distance from the object or surface at which it is directed
- Nanometer (nm): a unit of measure of wavelength of light (one billionth of a meter)
- Nanosecond: one billionth of a second
- Joule (J): unit used to measure the energy delivered
- Watts (w) and milliwatts (mw, 1/ 1000th of a watt): units used to measure the power capability
- Peak power output: the maximum output of power, measured in milliwatts and watts
- Average power: amount of power actually delivered in a given period of time
- Duty cycle: the amount of time the light is actually on during a given period of time
Lasers are of two principal types, “hot” and “cold”, and they are distinguished by the amount of peak power they deliver. “Hot” lasers deliver power up to thousands of watts. They are used in surgery because they can make an incision that is very clean with little or no bleeding and because the laser cauterizes the incision as it cuts. They are also used in surgery that requires the removal of unhealthy tissue without damaging the healthy tissue that surrounds it. “Cold” lasers produce a lower average power of 100 milliwatts or less. This is the type of laser that is used for therapeutic purposes and it is typically, although not always, pulsed. The light is actually on for only a fraction of a second because it is pulsed (turned on and off) at so many pulses per second. Pulsation results in an average power output that is very low compared to the maximum or peak output. Hence, most therapeutic lasers produce a high peak but low average power output. Therapeutic laser light is generally either visible (red, in most cases) or invisible (infrared). However, most therapeutic lasers operate at 904 nm which is an infrared light.