In the EU its "class based"
Vehicles at work - High visibility clothing
Are there any standards which the clothing should meet? HV clothing should be manufactured to a recognised standard. The new British Standard for high visibility warning clothing is BS EN 471. This is a harmonised European standard produced with the legal requirements for PPE in mind. Clothing which conforms to the standard is marked with a pictogram like this:
The first number (X) indicates the class of conspicuity, this depends on the minimum area of conspicuous materials that are incorporated into the clothing, with Class 3 being the best and Class 1 the lowest; the second number (Y) indicates the retroreflection performance with Class 2 being more visible than Class 1 when seen in headlights during darkness. The standard gives specifications for coveralls, jackets, waistcoats, tabards, trousers and harnesses.
From July 1995, new clothing must be 'CE' marked to show it meets the new European rules on the manufacture of PPE. Remember: the CE mark only means that the clothing meets the standard. It does not mean it can be used in all situations. HV clothing must be suitable for the actual conditions of use