UV400 means a sunglasses lens blocks light with wavelengths up to 400 nanometres. That covers all UVA and UVB rays, which is why UV400 lenses are often described as giving 100% UV protection.
It's one of the most important things to check before you buy sunglasses, and it's easy to confuse with how dark a lens looks. Here's what the label means, why it matters, and how lens filter categories fit in.
What is UV light?
Ultraviolet (UV) light is part of sunlight, but we can't see it. It has shorter wavelengths than visible light. Two types reach us at ground level:
- UVA has longer wavelengths, from about 315 to 400 nanometres.
- UVB has shorter wavelengths, from about 280 to 315 nanometres.
A third type, UVC, is absorbed by the atmosphere before it reaches the ground. Too much UV can harm your eyes and the delicate skin around them, and over time it's linked to eye problems such as cataracts. That's why UV protection is the first thing to check on any pair of sunglasses.
What UV400 means
A UV400 lens blocks light with wavelengths up to 400 nanometres. Because UVA ends at around 400 nanometres, a UV400 lens blocks both UVA and UVB.
You'll also see labels such as "100% UV protection" or "100% UVA/UVB protection". These describe the same level of cover. Be wary of vague claims like "UV protective" with no detail, and look for a clear statement instead.
Every pair of Yume sunglasses has UV400 lenses, whatever the frame shape or lens colour.
Dark lenses are not the same as UV protection
It's easy to assume a darker lens protects you more. It doesn't. How dark a lens looks tells you how much visible light gets through, which affects comfort. UV protection is a separate property of the lens, and a light lens can block UV just as well as a dark one.
In fact, a dark lens without UV protection can be worse than wearing no sunglasses at all. Behind a dark lens, your pupils open wider to let in more light, so more UV can reach the inside of your eye. A clear UV400 label matters more than the shade of the tint.
Lens filter categories 0 to 4 explained
UV400 tells you what a lens blocks. The filter category tells you how dark it is. Under the standard EN ISO 12312-1, sunglasses lenses are grouped by how much visible light they let through.
| Category | Visible light let through | Best for |
|---|---|---|
| 0 | 80-100% | Clear or very light tints, not for sunny days |
| 1 | 43-80% | Low sunlight |
| 2 | 18-43% | Medium sunlight |
| 3 | 8-18% | Bright sunlight, the most common choice for summer |
| 4 | 3-8% | Very bright conditions, such as glaciers. Not suitable for driving |
Most Yume lenses are Category 3, which suits bright days in the city or on holiday. A couple of our styles have lighter tinted lenses: the light blue Mirae Black/Blue and the rose-tinted Noxie Black/Red. They still block 100% of UVA and UVB, but they let more visible light through, so they feel less shaded in strong sun. You can see more colourful lenses in our tinted sunglasses.
Remember that category and UV protection are separate. A light lens can be UV400, and a dark lens may not be.
How to check a pair of sunglasses
- Look for the label: UV400 or 100% UVA/UVB protection should be clearly stated on the product page, label or packaging.
- Check the category: it's often printed inside an arm, for example "Cat 3".
- Think about where you'll wear them: Category 3 suits most bright days. Category 4 is only for very bright conditions and isn't suitable for driving.
- Don't wear tinted sunglasses for night driving: any tint reduces how much you can see in the dark.
If glare from water or wet roads is your main concern, read our guide to polarised vs non-polarised sunglasses.
FAQs
Is UV400 the same as 100% UV protection?
Yes. Both mean the lens blocks all UVA and UVB rays, which covers wavelengths up to 400 nanometres.
Do I need UV400 sunglasses in the UK?
Yes. UV can still reach your eyes on cloudy days, and water, sand and snow reflect it back towards you. UV400 lenses are a sensible choice all year round.
Do polarised lenses give more UV protection?
No. Polarisation cuts reflected glare, but it doesn't add UV protection by itself. Always check for UV400, whether a lens is polarised or not.
Are all Yume sunglasses UV400?
Yes. Every pair has UV400 lenses that block 100% of UVA and UVB, including our lighter tinted styles.
Looking for a pair you can trust in bright sun? Browse our best-selling sunglasses, all with UV400 lenses.
