Sunglass lens category numbers, from 0 to 4, describe how dark a tint is — nothing more. Category 0 is barely tinted, category 4 is very dark and unsuitable for driving. The number has no bearing on UV protection, which is a separate rating entirely, usually shown as UV400.
What do the category numbers actually measure?
They measure how much visible light the lens lets through, graded on a scale set out in the EN ISO 12312-1 sunglasses standard. A low number is a light tint, a high number is a heavy one. That’s the whole job of the category system — it says nothing about whether the lens blocks UV.
This is the point that trips people up, and it’s worth being blunt about it: a dark lens without a stated UV rating is worse than wearing no sunglasses at all. Darkness makes the pupil open wider. If no UV filter is doing its job behind that tint, more ultraviolet light reaches the eye than would in daylight with no glasses on. Look for UV400 or “100% UVA/UVB” printed on the lens or the docket — that’s the protection. The category number is styling and comfort, not safety.
What does each category from 0 to 4 mean?
Each category corresponds to a band of tint darkness, running from almost clear through to very dark. None of them imply anything about UV filtering on their own.
- Category 0 — Very light tint, sometimes closer to clear. Common on fashion lenses worn indoors or at dusk, or as a base for photochromic lenses before they’ve darkened.
- Category 1 — Light tint. Suited to overcast conditions or low sun, not strong daylight.
- Category 2 — Medium tint. This is the everyday, general-purpose category most people reach for without thinking about it.
- Category 3 — Dark tint. The standard choice for strong sun, beach, and most everyday sunglasses sold as “proper” sun protection.
- Category 4 — Very dark tint, intended for intense glare — high altitude, glacier, open water. Category 4 lenses are generally not permitted for driving because they let through too little light for safe road use, particularly at dusk or in tunnels.
Most sunglasses sold for everyday wear sit in category 2 or 3. Category 4 is a specialist tint, not a fashion upgrade.
Does a darker category mean better sun protection?
No. Darkness and UV protection are entirely different mechanisms, and a lens can score high on one and nothing on the other. A category 3 lens with no stated UV rating offers no more protection than a clear pane of glass — arguably less, for the pupil-dilation reason above.
For the actual protective element, what a UV400 rating actually means on sunglasses is worth understanding properly, because it’s the figure that matters, not the category number. If a pair only advertises its category and says nothing about UV, that’s a gap worth asking about before buying.
How does this relate to polarised lenses?
Category and polarisation are also unrelated, though people often assume a dark, glare-cutting lens must be polarised. It isn’t necessarily. Polarisation is a coating that cuts horizontal glare — off water, wet roads, bonnets — while category is simply overall tint darkness. A lens can be category 3 and not polarised, or category 1 and polarised.
What polarised lenses actually do is a genuinely different job from tint depth, and UV protection vs polarisation is worth reading side by side with this if the three terms — category, UV, polarised — are getting muddled on a spec sheet. It’s also worth knowing that polarised lenses are a bad idea in a few specific situations, such as reading certain digital screens or LCD displays clearly.
Which category should someone actually choose?
This is a comfort and conditions question, not a medical one, and the honest answer depends on where the glasses will be worn. Coastal glare, snow, and midday sun call for a darker tint; city walking or an overcast climate rarely does.
A few practical starting points, offered as general observation rather than rule:
- Category 2–3 covers the overwhelming majority of everyday situations in a temperate climate.
- Category 4 is a specialist choice for intense glare, not a default “premium” option, and isn’t appropriate for driving.
- Photochromic lenses, which shift between categories as light changes, suit people who move between indoors and bright outdoors often — though how quickly and how far they darken varies by lens and isn’t something to guess from category number alone.
None of this replaces a conversation with an optician about anything that touches actual vision or eye health — category numbers are a comfort and light-management spec, and any question about prescription lenses, tint suitability for a specific eye condition, or discomfort in bright light is properly theirs to answer, not a styling site’s.
Does blue-light filtering fit into this system?
No — blue-light filtering is a separate marketing claim, usually aimed at screen use, and it sits outside the category 0–4 tint scale entirely. The evidence that filtering blue light from screens meaningfully protects eyes or improves sleep is thin, and considerably behind the marketing built around it. It’s not a claim this site will repeat as settled fact, nor dismiss outright — it’s simply unproven either way at present, and shouldn’t be confused with a sunglass category rating or a UV rating, both of which rest on established standards.
What should actually be checked before buying a pair of sunglasses?
Category number is one line on a label — the more useful checks sit around it. A dark lens with no UV mention, or a UV mention with no category disclosed, are both signs to ask more questions rather than assume.
- Confirm UV400 or “100% UVA/UVB” is stated, separately from the tint category.
- Check the category suits where the glasses will actually be worn — driving, daily wear, or specialist glare.
- If polarisation is claimed, that’s a separate spec from both of the above, worth verifying on its own terms.
- Frame construction and lens material matter too — what makes a frame look expensive covers the build cues worth checking beyond the lens spec sheet.
Category numbers are a useful, standardised shorthand for tint darkness — genuinely worth understanding so a label makes sense at a glance. But they answer a comfort question, not a safety one. For the safety question, the only figure that matters is the UV rating, and for style, the far more interesting decisions live elsewhere — in frame shape and proportion, and in the broader world of sunglasses styling and lens and coating choices that actually change how a pair looks and performs day to day.
The Designer Glasses publishes general information and style opinion, not professional advice. We are writers and enthusiasts, not opticians, optometrists or dispensing opticians. Nothing here interprets a prescription, recommends a lens power, or tells you whether you need correction — only an eye examination can do that. If your vision changes suddenly, or you have eye pain, flashes, new floaters or halos around lights, treat it as urgent and contact an eye care professional the same day. Sunglasses should carry a stated UV rating: a dark lens without UV filtering is worse than none at all.