What does UV400 mean? UV400 vs category 3 vs polarised, explained
Short answer: UV400 means the lenses block ultraviolet light with wavelengths up to 400 nanometres – that covers both UVA and UVB rays. Category 3 is something else: it tells you how dark the lens is, meaning how much visible light gets through. Polarised is a third thing: a filter that cuts glare from reflective surfaces. A good pair of everyday sunglasses has UV400 protection and a category that suits the light you're in. Polarisation is an optional extra.
The three labels often sit side by side on the same swing tag, which is why they get mixed up. Here's what each one means, how they differ, and how to check a pair before you buy.
What does UV400 mean on sunglasses?
Ultraviolet (UV) light is invisible radiation from the sun. The part that reaches the ground is UVB (roughly 280–315 nm) and UVA (roughly 315–400 nm); UVC is absorbed by the atmosphere. A lens marked UV400 filters out UV radiation up to 400 nm, so it covers the whole UVA and UVB range.
You'll also see "100% UV protection" or "UV protection 400". In practice, they point to the same thing: the lens stops the UV range that matters for your eyes. What UV400 does not tell you is how dark the lens is. A pale lens can be UV400, and a very dark lens can lack a proper UV filter.
What does category 3 mean, and is it the same as UV400?
No. The category (also called filter category, or "cat.") describes how much visible light passes through the lens. It's defined in the European standard for sunglasses, EN ISO 12312-1, and runs from 0 to 4:
| Category | Visible light let through | Typical use |
|---|---|---|
| 0 | 80–100% | Clear or barely tinted; comfort and style, not for sun |
| 1 | 43–80% | Light tint; overcast days |
| 2 | 18–43% | Medium tint; moderate sun |
| 3 | 8–18% | Dark tint; bright summer sun – the classic sunglasses category |
| 4 | 3–8% | Very dark; high mountains, glaciers and snow. Not suitable for driving |
So "UV400, category 3" means the lens blocks UV up to 400 nm and is dark enough for bright sun. The two labels answer different questions, and you want both on the tag.
Is UV400 the same as polarised?
No. Polarised lenses contain a filter that blocks light reflected off flat surfaces such as water, wet roads, snow or a car bonnet. That reflected light is what you experience as glare. Polarisation makes things look calmer and crisper in those conditions, but it doesn't add UV protection on its own – a polarised lens still needs a UV filter to protect your eyes.
Polarised lenses come with a few trade-offs, too. Some phone, dashboard and cash-machine screens can look dark or patchy through them, and some skiers prefer non-polarised lenses because glare off ice can be a useful warning.
UV400, category 3 or polarised: which do you actually need?
- Everyday city use and summer holidays: UV400 and category 3. Polarisation is nice to have, not a must.
- Driving in daylight: UV400 with category 2 or 3. Never category 4 behind the wheel, and no tinted sunglasses after dark.
- Sailing, fishing or long days by the water: UV400, category 3 – and polarised if glare bothers you.
- High mountains and glaciers: UV400 with category 4, ideally with good side coverage.
- Grey, overcast days: UV400 with a lighter category 1 or 2 lens. UV reaches you through cloud cover, even when it doesn't feel sunny.
How can you check the UV protection on a pair of sunglasses?
- Look for "UV400" or "100% UV protection" on the tag, the product page or the inside of the temple.
- Look for the category number (0–4). In the EU it's often printed on the inside of the temple or on the tag as "cat. 3".
- Look for the CE mark. Sunglasses sold in the EU must carry it. It means the manufacturer declares that they meet the applicable safety requirements.
- Don't judge by darkness or price. A dark lens without a UV filter can be worse than no sunglasses at all, because your pupils open wider behind the tint and let more UV in. Protection comes from the filter, not the price tag.
What UV protection do ECO SHADES sunglasses have?
All ECO SHADES lenses are made from recycled PMMA and are listed as certified UV400 on every product page. Our plant-based acetate sunglasses – frames that are plant-based, 100% biodegradable and industrially compostable – are also listed as category 3. One example is the round Costa Blue with grey-tinted lenses. Our lenses are not polarised, and we don't sell them as such.
Prefer a frame in recycled plastic? Every model in our recycled collection has the same UV400-certified recycled PMMA lenses, in frames designed in Denmark.
FAQ
Is UV400 the same as 100% UV protection?
In everyday use, yes. Both mean the lens blocks UVA and UVB rays up to 400 nm.
Are darker sunglasses better for your eyes?
Not automatically. Darkness (the category) is about comfort in bright light. Protection from UV comes from the UV filter, so check for UV400 whatever the tint.
Can I drive with category 3 sunglasses?
Yes, category 3 is fine for driving in daylight. Category 4 lenses are too dark for driving, and you shouldn't drive with sunglasses at dusk or at night.
Do polarized sunglasses protect better against UV?
No. Polarisation reduces glare, while UV protection comes from the UV filter. A polarised lens without UV400 won't protect your eyes from UV.
