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. |
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- Examples
- 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.
- 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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