ISO 3864-4:2011 establishes the colorimetric and photometric requirements and test methods for the colours of safety signs to be used in workplaces and public areas. It provides the colorimetric and photometric specifications for the named safety and contrast colours prescribed in ISO 38641. The physical requirements that safety signs have to meet are primarily related to daytime colour and normally lit environments. ISO 3864-4:2011 also includes the colorimetric requirements and test methods for safety signs and phosphorescent material which also operate in unlit environments. ISO 3864-4:2011 is applicable to all locations where safety issues related to people need to be addressed. However, it is not applicable to signalling used for guiding rail, road, river, maritime and air traffic and, generally speaking, to those sectors subject to a regulation that may differ. The colorimetric and photometric properties of retroreflective safety signs, retroreflective materials combined with fluorescent or phosphorescent materials, or luminous safety signs activated by a radioactive source are not specified in ISO 3864-4:2011.