This European standard specifies requirements for automatic welding filters which switch their luminous transmittance to a lower predetermined value when a welding arc is ignited (referred to as welding filters with switchable scale numbers). It also specifies requirements for automatic welding filters which switch their luminous transmittance to a lower value, where the lower value of luminous transmittance is set automatically in dependence on the illuminance generated by the welding arc (referred to as welding filters with automatic scale number setting). The requirements of this standard apply if such a filter is to be used for continuous viewing of the welding process, (including gas welding and cutting), and if it is to be used only during the period when the arc is being ignited. These filters are used in welders' eye protectors or are fixed to equipment. If they are to be used in welders' eye protectors, other applicable requirements for these types of filters are given in EN 166. The requirements for the frames/mountings to which they are intended to be fitted are given in EN 175. Guidance on the selection and use of these filters is given in annex A. The specifications for welding filters without switchable luminous transmittance are given in EN 169.