EN166 is the core technical standard which applies to all safety eyewear including spectacles, goggles and visors. It does not apply to eye protection for which separate standards exist (anti-laser eye protection; sunglasses for general use)
The main tests for this standard are: Optical Requirements and Mechanical Protection/Impact Resistance
1. Optical Requirements
Tests include, transmission and diffusion of light, refractive properties, resistance to aging (stability to heat and resistance to UV), corrosion and ignition. Results of the testing define the Optical Class of the eye protector: which falls into 1 of 3 categories, where 1 is the highest and 3 is the lowest as indicated in the table. These categories define the quality of the lens in terms of how much or how little distortion is experienced by the wearer.
2. Mechanical Protection/Impact Resistance
This test (applicable to both lens and frame) determines the impact resistance of the eye protector (spectacles, goggles or visors) to withstand flying objects without cracking or shattering. This test is performed with steel balls of different diameters and weights which are used to strike the lens and frame at different speeds as indicated in the table.
This results in 4 levels of mechanical protection denoted by the markings: S, F, B or A on the eye protector where S is the lowest grade offering the least amount of protection and A is the highest grade offering maximum protection under the standard.