How do” Auto Darkening” welding helmets work and how dark should my welding helmet shade be?

Auto-darkening helmets, Figure 1, work basically by sensing the light from the arc and electronically activating a liquid crystal filter within the lens to darken to a preselected shade and protect the welders face and eyes from ultraviolet and infrared radiation (UV/IR). Most auto-darkening helmets use a solar cell array which captures the light from the welding arc and signals the Electro-optic welding lens to darken within 1/25,000 of a second.


Figure 1, Typical Auto-Darkening Helmet

The shade adjustment control allows the welder to choose whatever shade required for the welding process used and the intensity of the amperage. The shade selection is normally 9 to 13, but some models offer shade selection from 5 to 9 for grinding and cutting materials using Oxy-Fuel or Plasma and then 9 to 13 for arc welding. The desired shade requirement can be found in safety literature from the helmet manufacturer or in welding safety standards such as CSA W117.2 Standard for Safety in Welding, Cutting and Allied Processes. Figure 2 below is extracted from Table 7 of CSA W 117.2 and illustrates a shade selection chart for different processes and current levels for arc welding and thicknesses for Oxy-Acetylene welding and cutting.

csa chart

csa chart 2

Figure 2. Welding Helmet Lens Shade Selection

(Source: Table 7, CSA W117.2:19, Safety in welding, cutting, and allied processes. © 2019 Canadian Standards Association. Please visit

Bill Eccles, Vice President, PPC and Associates