EN 207 - Scale Numbers

Scale Numbers

The scale numbers range from L1 to L10, where the number is a lower limit for the optical density, i.e. Ln means that OD > n, or, where T is the transmittance. The minimum scale number for a given laser depends on the working mode and the wavelength as follows:

Working mode Wavelength range Maximum laser
power density		 Minimum protection level
for given power*
D (continuous) 180–315 nm 1×10n-3 W/m² log(P) + 3
315–1400 nm 1×10n+1 W/m² log(P) - 1
1400 nm–1000 μm 1×10n+3 W/m² log(P) - 3
I,R (pulsed) 180–315 nm 3×10n+1 J/m² log(E/3) - 1
315–1400 nm 5×10n-3 J/m² log(E/5) + 3
1400 nm–1000 μm 1×10n+2 J/m² log(E) - 2
M (ultrashort pulses) 180–315 nm 1×10n+10 W/m² log(P) - 10
315–1400 nm 1.5×10n-4 J/m² log(E/1.5) + 4
1400 nm–1000 μm 1×10n+11 W/m² log(P) - 11
*P in W/m², E in J/m².
Level numbers should be rounded upwards.
Examples
  1. the laser operates at 1064 nm and has a pulse duration of 10 ns, 100 mJ/cm2 (or 103 J/m²). You have goggles that are specified as DIR 1064 L5. The pulse duration indicates that we should look at the R specification, with scale number n=5, which gives an upper limit of 5×102 J/m², which means that these goggles do not offer suitable protection for this particular laser.
  2. the laser operates at 780 nm, is continuous wave with a power of 50 mW/cm2 (P = 500 W/m²). This means you need a D protection level of, which is rounded up to 2. In other words, the safety goggles should be at least D 780 L2.

From the scale it can be inferred that the power densities that correspond to are considered safe without protective eyewear.

Read more about this topic:  EN 207

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