EN ISO 20471 High Visibility warning clothing ISO 20471:2013 specifies requirements for high visibility clothing which is capable of visually signaling the user's presence. The high visibility clothing is intended to provide conspicuity of the wearer in any light condition when viewed by operators of vehicles or other mechanized equipment during daylight conditions and under illumination of headlights in the dark. Performance requirements are included for colour and retro-reflection as well as for the minimum areas and for the placement of the materials in protective clothing.