The CE mark is a mandatory European marking for certain product groups to indicate conformity with the essential health and safety requirements set out in European Directives. In the case of eyewear it indicates conformity with PPE Directive 89/686/EEC and European Standard BS EN 1836:2005. (PPE stands for Personal Protective Equipment).
There are five categories that describe the amount of tint in sunglasses.
Category 0
Clear or very light tint: a clear lens for ordinary glasses and protection
Category 1
Light tint: usually a yellow or orange lens, often worn by cyclists, and is for protection against grit from the road as well as for enhancing low light in winter
Category 2
Medium tint: usually a blue lens and will protect against sunlight but not at altitude or where there is reflection from sand and water
Category 3
Dark tint: the most common available for sunglasses and is good for low mountain altitudes, the seaside and bright days
Category 4
Very dark tint: essential in high mountains above 3000 metres, regardless of whether there is any snow. These lenses are not recommended for driving as they are too dark
