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How auto-darkening filters work

3M™ Speedglas™ Auto-Darkening Filters (ADF) turn dark the moment an arc is struck and transparent again when welding stops – all the time with full UV/IR protection. ADF layers

Each Speedglas filter is a laminate of diffent layers: a UV/IR filter (A), three polarizers (B) and three liquid crystal elements (C). The UV/IR filter continually blocks harmful radiation, regardless of whether the filter is in the light or dark state or whether the auto-darkening function is operational. Aided by surface-mounted electronics, the proprietary liquid crystal elements act as shutters that detect and react to the welding arc by instantly becoming either dark, or light, as needed.

The level of protection from the UV/IR filter is constant; equivalent a shade 13 passive welding filter.

Before welding:How an ADF works
With the auto-darkening welding helmet in the safe down position, you can clearly see through the welding filter. Both of your hands are free and the electrode can be precisely positioned.

During welding:
Within 0.1 ms (in room temperature) of the arc strike, the filter has switched to the dark state.

After welding: The filter automatically returns to the light state after welding is complete, allowing your immediate and safe inspection of the weld pool, as well as preparation for the next weld.

Watch: Is there a better way to see what you are welding?

3M™ Speedglas™ Welding Helmets incorporating auto-darkening filters apply to the European Standards EN 175, EN 166 and EN 379 as well as many National Standards. For further information please contact 3M Customer Service in your country (


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