The arrival of electronic auto-darkening filters (ADF) to the world of welding in the early 1990s has increased the safety levels of workers in the sector considerably. The big difference between traditional dark welding filters and ADFs is that the latter offer permanent filtration of harmful rays from welding, regardless of the dark tone of the filter. That is, even in the event that the electronic filter, for some reason, does not darken, its filtration is guaranteed and therefore the protection of sight is permanent.

Without an electronic filter, a welder cannot see through glass without an electric arc, which is why welders often had eye injuries such as conjunctivitis or cataracts, as they had to take the welding mask out of sight in order to distinguish where to make the spot weld. Furthermore, a poor choice of dark shade led to inadequate filtering of harmful rays (UV, blue light and IR).

ADFs must meet minimum requirements, safety and quality requirements set out in the EN 379: 2004 + A1: 2010 standard.

The standard requires 4 different optical quality tests for electronic filters. These tests, according to the results, will be translated into notes and will be indicated on the CE certificates that will be obligatorily marked on the electronic filters.

The first grade, which can be 1 or 2 (1 as the best grade), refers to the optical class:

• 1: optical class 1, without limitation of use (a maximum deviation of +/- 0.06 diopters is allowed).
• 2: optical class 2, limited use (maximum deviation of +/- 0.12 diopters is allowed).

The second note, which could be (from best to worst) 1, 2 or 3, points to diffraction (angles of light rays passing through the optical streak of electronic filters). The higher the diffraction, the image will be perceived less sharply.

The third note distinguishes the homogeneity of the dark tone between the entire optical surface of the electronic filter. Here again, the best score would be 1, 3 the worst. The test is carried out by contrasting the tonality in the four corners and in the center, the tone in the five areas should be equal for maximum homogeneity.

The fourth note corresponds to the angular dependence. This test was the last one incorporated in 2010 at the time of the revision of the standard.

All liquid crystals have the particularity that their angle will affect a more accentuated clarity. Digital clocks, televisions, monitors, … always have a tolerance angle beyond which it is not possible to see the image. Due to this natural phenomenon, in the case of electronic filters, welders can perceive by tilting their head that the filter reveals lighter shades as the angle of inclination increases. Some manufacturers of electronic filters have developed liquid crystals with compensation for the angular dependence of the filter, in such a way that when the welder tilts his head, the dark tone will not support any variation. Following the same arrangement: 1 the best grade, 3 the worst.

Example of marking on an electronic welding filter:

4/9-13 DAC 1/1/1/2 EN379 CE

• 4: value that indicates the light tone.
• 9-13: refers to dark tones from 9 to 13.
• DAC: manufacturer (Dacar).
• 1: optical class
• 1: diffraction
• 1: homogeneity
• 2: angular dependence
• EN379: reference standard
• CE: official logo