Optical clarity is the accuracy of the vision. Welding helmets have EN 379 1-3/1-3/1-3/1-3 optical clarity rating. These ratings depend on 4 tests, Optical class / Diffusion of light class / Variations in luminous transmittance class / Angle dependence on luminous transmittance class. All these tests give number 1 to 3. 1 for best and 3 for worst results.