UV400 vs polarized: they are not the same thing, and you want both

UV400 and polarized are two different claims about two different things. UV400 means the lens blocks ultraviolet light up to a wavelength of 400 nanometres, which is the whole UVA and UVB range; it is what protects your eyes. Polarized means the lens contains a film that removes reflected glare; it is what makes water, roads and snow easier to look at. A lens can be UV400 and not polarized, polarized and not UV400, both, or neither. If you are buying sunglasses to wear outdoors, you want both, and you should check for both separately.

What UV400 means

Ultraviolet light sits just beyond the violet end of what the eye can see. The part that reaches the ground runs from about 280 to 400 nanometres: UVB at the short end, UVA at the long end. Both are associated with damage to the cornea, the lens of the eye and the retina over time, which is why eye-care bodies recommend UV-blocking sunglasses whenever you are in bright sun.

"UV400" is the plain statement that the lens absorbs everything up to 400 nm. That covers UVA and UVB entirely. It is the strongest common UV claim on a sunglasses label.

"UV protection", "blocks UV" or "UV coating" without a number is a weaker claim. It says some ultraviolet is blocked; it does not say how much, or up to what wavelength. It might be UV400 in practice. It might not.

UV protection comes from the lens material and its coating, not from the tint. A clear lens can be UV400. A very dark lens can block none.

What polarized means

A polarized lens has a film inside or on it made of molecules aligned in one direction. Light vibrating along that direction is absorbed; light vibrating across it passes. Because glare, the light bouncing off a flat surface, arrives vibrating mostly horizontally, a film set to block the horizontal plane removes most of it and leaves the rest of the scene alone.

That is the whole of what polarized means. It does not describe darkness, colour or UV. Our polarized vs non-polarized post goes through when it helps and when it does not.

Why the confusion is dangerous

Darkness is the property people notice, and it is the one that tells you the least. A dark lens makes your pupils open wider. If that dark lens does not block UV, more ultraviolet reaches the back of the eye than if you wore nothing. Eye-care bodies are direct about this: a dark lens without UV protection is worse than no sunglasses.

So the order of importance, for your eyes, is:

1. UV protection. Non-negotiable. Look for a stated UV claim, and prefer UV400 or "100% UVA/UVB".
2. Polarization. A large comfort and visibility gain near water, roads and snow. Not a safety feature.
3. Darkness and tint. A matter of the light you are in. Our lens colour guide covers it.

How to read a label

What our lenses claim, precisely

We buy our frames against a listing that states "UV protection coating" and "polarized". It does not state UV400 or a cut-off wavelength. So this site says the lenses are polarized and carry a UV-protective coating, and it does not say UV400, because nobody has put one on a spectrometer and the maker has not claimed it. You will see that wording on every product page. It is a weaker claim than we would like to make, and it is the one the evidence supports.

For children the UV claim matters even more, and our kids' sunglasses post explains why. If UV400 specifically matters to you, and for high-altitude or all-day use it should, ask for it in writing from whoever you buy from, or have an optician check a pair with a UV meter.

Frequently asked questions