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    Lasers approved for cold laser therapy are classified as class 1, 1M, 2, or 2M.  They have a wavelength towards the red visible spectrum or near infrared (635-970nm) and have low energy outputs. 

    Lasers are classified based upon the wavelength of light that is emitted and by the maximum power output that they are able to achieve.  Since each laser puts out a specific wavelength of light, it is listed on the laser by the manufacturer. Acceptable power output is measured via the maximum permissible exposure (MPE), which is the highest power or a light source that is considered safe.  Safe is defined as 10% of the dose that has a 50% chance of creating damage to tissues under the worst conditions.  With regard to power output, lasers are placed in one of 4 categories, see table below. 

Class

Description
1 A class 1 laser is safe under all conditions for normal use.  The MPE cannot be exceeded.  This also includes high power lasers enclosed within a protective casing.
1M Class 1M lasers are safe at all times except when passed through a magnifying apparatus.  The MPE is not able to be exceeded unless the beam is magnified or focused in some way.  Only applies to lasers with a large or divergent beam.
2 Class 2 lasers are considered safe because the blink reflex limits exposure time.  This is only applicable for visible-light lasers (wavelengths 400-700nm).  These lasers are limited to 1mW of continuous energy output or a pulse time of <0.25 seconds.  Most laser pointers fall into class 2.
2M As with 1M lasers, Class 2M lasers are safe, via the blink reflex, unless magnified or focused in some manner.  Only applies to large beam or divergent beam lasers.
3R Class 3R lasers are safe, if handled carefully and with restricted beam viewing.  It is possible to Exceed the MPE, but there is a low risk of injury.  Maximum power output is limited to 5mW.  Further power restrictions apply for non-visible light wavelength lasers.
3B Class 3B is considered hazardous if the viewed directly.  Wavelengths from 315nm to the far infrared are limited to 500mW of power output.  for pulsed lasers with a wavelength of 400-700nm (visible light) power output is limited to 30mW.  Protective eyewear is required when working with class 3B lasers.  These lasers must also be equipped with a lock and key safety switch.
4 Class 4 includes all lasers that do not fall into the previous categories, essentially any laser with a greater power output than class 3B.  By definition, a class 4 laser can burn the skin and will cause permanent and devastating ocular damage if viewed directly.  These lasers may ignite material.  Class 4 lasers are also required to have a lock and key safety switch.  Most industrial, scientific, military and medical lasers are class 4.

    Lasers approved for cold laser therapy are classified as class 1, 1M, 2, or 2M.  They have a wavelength towards the red visible spectrum or near infrared (635-970nm) and have low energy outputs. 

    The low energy output and specific wavelength range for a cold laser has been reported to coincide with biological activity. See Benefits for further discussion.