Sunglasses Standards Decoded: What the Markings on Your Frame Mean
Standards
Sunglasses Standards Decoded: What the Markings on Your Frame Mean
CE, ISO 12312-1, lens category numbers and UV400. A plain-English guide to the marks stamped inside a temple arm and what each one actually guarantees.
In this article
- Where the markings live
- ISO 12312-1: the international baseline
- The CE mark and what it does not tell you
- Lens categories 0 to 4
- UV400 is a specification, not a certification
- Marks that mean nothing
- How to read a frame in ten seconds
- Frequently asked questions
Where the markings live
Almost every marking on a pair of sunglasses is printed or engraved on the inside of the temple arm, the part that runs towards your ear. On some frames it sits on the inside of the bridge instead.
You will typically find some combination of the model name, the size string, a lens category number, and a standards reference. Most buyers never look, which is how a lot of unprotected eyewear gets sold.
ISO 12312-1: the international baseline
ISO 12312-1 is the international standard for sunglasses intended for general use. It is the reference point that most national standards now align with.
It sets requirements across several areas at once: how much ultraviolet the lens transmits, which lens category it falls into, optical quality and freedom from distortion, mechanical robustness, and how the product must be labelled.
The part most people care about is transmittance. A lens meeting the standard must keep ultraviolet transmission within defined limits for its category, which is what turns a dark lens into a protective one.
The CE mark and what it does not tell you
In Europe, non-prescription sunglasses are treated as personal protective equipment, and the CE mark indicates the manufacturer declares conformity with the relevant requirements.
Two things are commonly misread here. First, CE is a declaration by the manufacturer, not a certificate issued by an independent testing body in every case. Second, CE tells you a claim has been made. It does not tell you the lens category or the exact ultraviolet cut-off. For that you need the category number and the standard reference.
A CE mark alone, with no category number and no standard reference anywhere on the frame or packaging, is thin information.
Lens categories 0 to 4
The category number describes how much visible light the lens lets through. It is about darkness, not about ultraviolet protection, and this is the single most misunderstood point in the whole system.
| Category | Light transmitted | Typical use |
|---|---|---|
| 0 | 80 to 100% | Clear or very light tint, indoor and evening |
| 1 | 43 to 80% | Light tint, overcast conditions |
| 2 | 18 to 43% | Medium tint, general daylight |
| 3 | 8 to 18% | Dark tint, bright sun, the most common category |
| 4 | 3 to 8% | Very dark, high altitude and glaciers |
Category 3 covers the vast majority of everyday sunglasses. Category 4 is specialist mountain eyewear and is not permitted for driving in many jurisdictions, because it cuts too much light for safe road use.
UV400 is a specification, not a certification
UV400 means the lens blocks wavelengths up to 400 nanometres, which covers the entire ultraviolet band that reaches the eye, both UVA and UVB. It is the most useful single number on a pair of sunglasses.
It is worth being precise about what it is. UV400 describes a performance level. It is not itself an accreditation scheme with an issuing body. Its value comes from being unambiguous: there is no partial UV400.
In good eyewear the filtering is built into the lens material rather than applied as a surface coating, which is why it does not wear off with cleaning or age the way a coating can. Every Rawbare lens carries 100% UV400 protection as standard.
Marks that mean nothing
A few things appear on eyewear and packaging that carry no testable meaning at all.
Generic claims such as anti-UV, UV protected or sun safe with no number attached. Without a wavelength figure or a standard reference, there is nothing to verify.
Percentage claims with no wavelength. Blocks 95% of harmful rays raises the immediate question: which rays, measured to what limit.
Lens darkness described as a protection level. Phrases such as extra dark protection conflate two unrelated properties.
A polarized sticker treated as a protection claim. Polarization is a glare technology. It is not a substitute for ultraviolet filtering, and the two are independent.
How to read a frame in ten seconds
Turn the left temple arm inwards to the light and look for three things in this order.
First, a category number, usually written as a single digit or as CAT 3. That tells you the darkness class. Second, a standards reference such as ISO 12312-1. That tells you a testable claim exists. Third, a UV figure, ideally UV400. That tells you the ultraviolet cut-off.
If all three are present, you have real information. If none are, you are relying entirely on the reputation of the seller, and for something you wear over your eyes in direct sunlight that is a thin basis for a decision.
Frequently asked questions
Key takeaways
