Page 113 - Lasers and IPLs in Medical/Aesthetic Applications v1.2
P. 113

Chapter 1 – Fundamentals of Medical/Aesthetic Lasers and IPLs v1.2
Furthermore, the optical density (OD) of the goggles must protect against the output power of the laser. For class 4 lasers utilising Q-switching technology this typically means an OD of 7 or more for each wavelength. All such goggles MUST comply with BS EN207:2017 (in the UK). (It should be noted that many Chinese manufacturers/suppliers do not supply the legally required safety glasses with their equipment! If you are unsure whether your glasses are safe, or not, please contact an LPA or other suitable laser expert).
Unless the goggles comply with both of these requirements they will not offer the full protection required. Goggles must be worn by every person in the laser-designated room at all times while the laser is active. They must not be removed until the laser is inactive.
 WARNING – EVEN A SMALL AMOUNT OF LASER LIGHT FROM A CLASS 4 LASER CAN DAMAGE THE EYE PERMANENTLY.
Laser Safety Eyewear – pulsed and continuous outputs
In addition to the energy output of lasers, the EN207:2017 directive also dictates ratings according to the pulse duration of lasers.
The directive requires that a laser safety glasses must be able to protect the user for a minimum of 10 seconds (D rating) or 100 pulses (I and R rating), without failure, when exposed to laser radiation.
The ‘pulse duration’ ratings are:
where tp is the pulse duration of the laser.
The ‘optical density’ scale number Ln scale takes into account the maximum energy or power density that a set of goggles can absorb in the minimum timeframe without performance degradation. This scale number is determined from the MPE tables in EN 207:2017. This scale goes from L1 to L10 and is further sub-divided into three bands according to wavelengths:
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Chapter 1 LEVEL A Fundamentals of Lasers/IPLs
     D
      Continuous output or tp > 0.2 seconds
    I
Pulsed outputs: 1 s < tp < 0.25 s
      R
  Pulsed outputs: 1 s < tp < 1 ns
      M
      Pulsed outputs: tp < 1 ns
      Band 1
     180 to 315 nm (UV)
    Band 2
 >315 to 1400 nm (UV-visible-NIR)
    Band 3
      >1400 nm to 1 mm (IR)
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