How to Read the Markings on Safety Eyewear: EN 166, EN 170 and EN 172

October 06, 2026 · 9 min read

Why the marking exists

Safety eyewear sold in Europe carries a compact code, moulded or printed onto the frame and sometimes onto the lens itself. It is not a brand label and not decoration. It is a declaration of which standard the product was tested against and which hazards it is intended to address. Reading it correctly is the difference between wearing eyewear suited to the job and wearing something that merely looks like it.

The parent standard and its family

EN 166 is the general requirements standard for personal eye protection. It covers construction, the field of vision, and the general physical requirements that all eye protectors must meet. It also establishes that a specific filter must satisfy these general requirements in addition to its own.

The hazard-specific members of the family sit beneath it:

• EN 169 - filters for welding and related techniques, with transmittance requirements and recommended use.
• EN 170 - ultraviolet filters, with transmittance requirements and recommended use.
• EN 171 - infrared filters, with transmittance requirements and recommended use.
• EN 172 - sunglare filters for industrial use, specifying scale numbers and transmittances.

So a product claiming EN 172 is claiming to have been tested as a sunglare filter for industrial use, and it must also satisfy the general requirements of EN 166. A product marked to EN 166 alone is not making a claim about any specific filter type. The distinction matters because a lens can be dark without being a certified sunglare filter, and can be a certified sunglare filter without being impact rated for the task in front of you.

Reading the letters: mechanical strength

The single letters that accompany the standard number describe impact performance. They run from a basic robustness requirement up through low, medium and high energy impact categories, with an additional letter used where the product has also been tested at temperature extremes. A lower-tier letter is not a statement that the eyewear is weak - it means the product was tested and passed against a lesser impact demand. What matters is matching the tier to the hazard. Eyewear rated for low energy impact is not a claim that it will stop everything, and eyewear rated for high energy impact is not automatically the right choice for a chemical splash or a dust problem.

Reading the numbers: optical class and field of use

Two further pieces of information appear in the code. An optical class number describes how much optical distortion the lens introduces: class 1 is the most optically accurate, with higher numbers permitting wider tolerances of power and prism. If you wear the eyewear for long periods rather than for seconds at a time, this is the number worth caring about, because distortion is a fatigue problem before it becomes a safety problem.

A field of use number identifies the specific hazard the protector or filter is intended for - liquid droplets and splashes, coarse dust particles, gas and fine dust, and the other categories defined for the standard. A field of use code is the product telling you what it was designed to stop, which is why the same frame style can exist in several distinctly different specifications, and why two pairs that look identical can carry completely different protective claims.

Why the code is worth reading before you buy

Shop descriptions are written to sell; the marking is written to a test. If you are buying protective eyewear for a workshop, a laboratory, a garden or a bicycle, the marking is the only claim you can check independently. It also travels with the product: a supplier's page may change, but the moulded code on the frame does not.

Where to find the marking, and what it looks like in practice

On spectacles the code usually sits on the temple, with the frame's own product code nearby. On goggles it is generally on the frame body, and where a lens carries a filter marking it may be repeated on the lens itself. A complete marking typically combines a standard number, an optical class number, a mechanical strength letter and one or more field of use numbers, alongside the manufacturer's identification and, for filters, a scale number.

Because these characters are printed small and wear away on working eyewear, it is worth recording the code while the product is new - a photograph of the temple is usually enough - so that you can re-order the same specification later rather than trying to reconstruct it from memory or from a shop listing that may have changed.

Common misconceptions

• "CE marked means it is safety eyewear." CE marking is a declaration of conformity to the applicable regulation. The EN 166 family code is what tells you the protective claim.
• "Dark sunglasses protect my eyes at work." Tint is not protection. A dark lens with no filter claim can suppress visible light while letting the hazard through, and sunglasses not intended for industrial use may never have been impact tested at all.
• "A higher impact rating makes a product better for everything." Impact strength says nothing about chemical splash, molten metal, dust sealing or optical accuracy. Each is a separate claim in the code.
• "The marking only matters for employers." It is just as useful for DIY, cycling or workshop use, because it is the one claim a shop's marketing text is not required to carry.

When to ask a professional

If you are buying eye protection for a workplace, the required specification should come from the risk assessment for the task, not from the product listing - ask which standards and which codes are mandated for the hazard you actually face. If you need prescription safety eyewear, ask a dispensing optician who supplies certified protective eyewear rather than assuming that an ordinary frame fitted with a certified lens is equivalent, because the frame is part of the protective system. And if you already own protective eyewear whose marking is absent, worn away or unreadable, treat the protective claim as unverified rather than assumed. The marking is the evidence, and no marking means no evidence.

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