The level of tissue penetration by the laser beam depends on the beam’s optical characteristics, as well as on the concentration and depth of the chromophores, which are absorbed at different percentages according to the laser light’s wavelength. For instance, water absorbs almost 100 percent of the laser irradiation at 10,600 nanometers, the wavelength of a CO2 gas laser. That is the reason why this type of laser wavelength is used in surgical applications. Other factors affecting the depth of penetration are the technical design of the laser device and the particular treatment technique used. There is no exact limit with respect to the depth penetrated by the light. The laser light gets weaker the further from the surface it penetrates where eventually the light intensity is so low that no biological effect from it can be measured. In addition to the factors mentioned, the depth of penetration is also contingent on tissue type, pigmentation and foreign substances on the skin surface such as creams or applied oils. Bone, muscles and other soft tissues are transparent to certain laser lights, which means that light can safely penetrate these tissues. The radiation in the visible spectrum, between 400 and 600 nanometers, is absorbed by the melanin, while the whole extension of the visible which goes from 420 to 750 nanometers is absorbed by composite tetrapyrrolics. In the infrared, which covers about 10,000 nanometers of light spectrum, water is the main chromophore. Fortunately, there exists a narrow band in the light spectrum where water is not a highly efficient chromophore, thereby allowing light energy to penetrate tissue that is rich in water content. This narrow band, which extends approximately from 600 to 1,200 nanometers, is the so-called “therapeutic window”. That is the reason why the lasers in the market today have wavelengths within the 600-1,200 nanometer limit. The penetration index is not at the same level throughout the therapeutic window. In fact, lasers in the 600 to 730 nanometer range have less penetration and are more suitable for superficial applications such as in acupuncture methodologies.