This European Standard specifies the scale numbers and transmittance requirements for filters for protection against ultraviolet radiation. The other applicable requirements for these types of filters and the frames/mountings to which they are intended to be fitted are given in EN 166. Guidance on the selection and use of these filters are given in annex B. NOTE The protective filters specified in this standard are not suitable for the direct viewing of bright light sources like Xenon high-pressure arc lamps or for the direct or indirect observation of an electric welding arc. For this purpose a welding filter as specified in EN 169 and with a scale number appropriate to the source being observed should by used.