How dark do lenses on welding helmets need to be?

According to OSHA, the radiant energy and light produced by welding, cutting, or brazing operations varies according to a number of factors including the task producing the light, the electrode size, and the arc current. To protect users who are exposed to this light, begin by selecting a shade too dark to see the welding zone. Then experiment with lighter shades until you find one that allows an adequate view of the welding zone without going below the minimum protective shade.