Page 104 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
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Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Note: The ‘star-burst’ laser warning symbol alerts people to the possible presence of laser radiation:
Figure 57: The international warning symbol for lasers
Maximum Permissible Exposure Levels - MPE
The MPE is the maximum power/energy level to which an individual may be exposed to laser light without inducing any tissue damage. It implies that any power/energy level below the MPE may be considered to be safe and not require the wearing of laser safety glasses.
However, the MPE depends on both the wavelength and the exposure duration, and is calculated for both the skin and eyes. MPEs are based upon biological data – not laser outputs.
MPEs vary according to the wavelength, exposure time, tissue at risk and for visible and near infra-red radiation, the size of the retinal image. For detailed information on MPEs and tables of values see Annex A, pages 56-62 of BS EN 60825-1:2014 or pages 49-52 of PD IEC TR 60825-14:2014.
There can be large variations in the MPE for the skin and the eyes, depending on the laser. As an example, for a continuous Helium-Neon laser operating at 633nm the MPEs are:
• intra-beam viewing - 1 mW/cm2 • skin exposure - 200 mW/cm2
This indicates that exposing this type of laser to the skin is much safer than exposing it to the eye, by a factor of 200!
Accessible Emission Levels – AEL
The AEL of a laser system is the maximum level of accessible laser energy to which any individual may obtain access during operation of that laser and still remain safe. It may be determined by the product of the MPE times an area known as the “limiting aperture” – for ocular exposure this limiting aperture is the maximum size of the human pupil (typically
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
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