Depth of penetration is defined as the depth at which 60% of the light is absorbed by the tissue, while 40% of the light will continue to be absorbed in a manner that is less fully understood. Treating Trigger points with Light can have a dramatic effect on remote and internal areas of the body through the stimulation of nerves, acupuncture and trigger points that perform a function not unlike transmission cables. 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. Visible red light, at a wavelength of 630-660 nanometers (nm - 1 nanometer is equal to one billionth of a meter), penetrates tissue to a depth of about 8-10 mm. It is very beneficial in treating problems close to the surface such as wounds, cuts, trigger and acupuncture points and is particularly effective in treating infections. Infrared light (800-1000nm) penetrates to a depth of about 30-40 nm which makes it more effective in the treatment of joints, deep muscle, etc.