"100% UV protection" means a lens blocks essentially all of the ultraviolet light that reaches your eyes from the sun. "UV400" means the same thing in a more technical way: the lens blocks light with wavelengths up to 400 nanometres, which covers the entire UVA and UVB range. In practice, the two labels describe the same level of protection.
Here is the part most people get wrong, and it matters more than the labels themselves: how dark a lens looks has nothing to do with how much UV it blocks. A pale lens can block 100% of UV, and a very dark lens can block almost none. UV protection comes from a coating or from the lens material itself, not from the tint.
Dark lenses without UV protection are worse than no sunglasses
This is the one thing to take away. Your pupil responds to visible brightness. Put a dark tint in front of your eye and the pupil opens wider to let more light in, because as far as your eye is concerned, the sun just went behind a cloud.
If that dark lens has no UV filter, the ultraviolet light is still coming through, and now it is pouring through a wider pupil. You have removed the natural defense of squinting and constricting without replacing it with anything. That is why unlabeled sunglasses from a gas station rack or a beach kiosk are a genuinely bad idea, and why "they're just for the drive home" is not a good enough reason.
Sunglasses with no UV rating are not a smaller version of good sunglasses. They are a different thing entirely. Every frame we sell blocks 100% of UV, which is a low bar that a surprising amount of cheap eyewear still fails to clear. If a pair does not state its UV protection anywhere on the tag, the packaging, or the product page, assume it does not have any.
UVA, UVB and UVC, briefly
Ultraviolet light sits just past the violet end of the visible spectrum and splits into three bands by wavelength. UVA runs roughly 315 to 400 nanometres, penetrates deepest, and makes up the large majority of the UV that reaches the ground. UVB runs roughly 280 to 315 nanometres, is the band most associated with sunburn, and varies a lot with time of day, season and altitude. UVC is the shortest and most energetic, and it is absorbed by the ozone layer before it reaches you, which is why eyewear does not need to account for it.
So what does the 400 in UV400 refer to?
The number is the wavelength cutoff in nanometres. A UV400 lens blocks light below 400 nm, and since UVA tops out at 400 nm and UVB and UVC sit below that, a UV400 lens has the whole ultraviolet range covered. That is the entire trick. There is no higher number to chase, and a lens advertised as UV380 stops short of the top of the UVA band.
You get a second dose from below
UV does not only arrive from overhead. It bounces. Water, wet sand, concrete and especially snow all reflect ultraviolet light back up at your face, which means you are lit from two directions at once on exactly the days you are outside longest.
Snow is the most reflective of the common surfaces, open water is next, and dry sand and pale concrete are meaningful too. Grass and soil reflect comparatively little. If you spend your days on a boat, a beach or a ski slope, the reflected component is not a footnote, and it is the reason sunglasses that only shade you from the top do an incomplete job.
Fit and coverage do real work
Light that goes around your lenses is light your lenses cannot filter. The gaps at the temple, above the brow and below the frame all let UV in unfiltered.
- Wrap styles curve with the face and close down the temple gap, which is why they are the default choice for boating, cycling and running.
- Larger lenses cover more of the skin around the eye, including the thin eyelid skin that also takes sun damage.
- Frames that sit close to the face reduce the reflected light sneaking up from below.
- Fit-overs are worth knowing about if you wear prescription glasses. Our fit-over sunglasses go straight over your everyday frames and are built with side shields, so they close the temple gap by design rather than by accident.
A hat with a brim helps with the light coming from above, but it does nothing about the light coming off the water. The two work together.
Lens categories 0 to 4, and why they are a separate question
Lens category numbers describe how much visible light a lens transmits. They are about comfort and glare, not about ultraviolet. A category 1 lens and a category 3 lens can both be UV400.
| Category | Roughly | Typical use |
|---|---|---|
| 0 | Clear or very light tint | Indoors, overcast, night |
| 1 | Light tint | Cloudy days, low sun |
| 2 | Medium tint | Variable sun |
| 3 | Dark tint | Bright sun, most general use |
| 4 | Very dark | Mountains and glaciers, not legal for driving in many places |
Most everyday sunglasses, including most of our latest styles, sit at category 3. Pick the darkness that suits your light conditions, then check UV separately.
The damage adds up, and children collect more of it
UV exposure is cumulative. There is no single afternoon that does the harm; it is the sum of every hour outdoors across decades, which is why sun protection is a habit rather than an event.
Children matter here because they tend to spend far more time outdoors than adults do, and a large share of a lifetime's UV exposure is collected before adulthood. Getting kids into sunglasses that actually block UV early is one of the easier wins available.
Cloudy days are not a day off either. A good deal of UV passes straight through cloud cover, so the sky can be gray and overcast and you can still be accumulating exposure. If you are outside for hours, wear the sunglasses.
Frequently asked questions
Is UV400 better than 100% UV protection?
No. They describe the same thing from different angles. UV400 states the wavelength cutoff, 100% UV protection states the outcome, and a lens meeting one meets the other.
Do polarized lenses block UV?
Not inherently. Polarization is a separate filter that cuts glare reflected off flat surfaces like water and roads. It is a comfort feature, and a very good one on the water, but it says nothing about UV. Check for both.
Can I tell by looking whether a lens blocks UV?
No. Ultraviolet light is invisible, so there is no color, darkness or mirror finish that tells you. You are relying on the label and on the seller, which is the argument against unlabeled bargain-bin sunglasses.
How often should I have my eyes checked?
An annual eye exam is a reasonable default for most adults, and your eye doctor can advise a different interval based on your history. We are not a prescription eyewear retailer, so take any specific concern about your eyes to a doctor.
What to do with all this
Buy sunglasses that state their UV protection, choose a tint darkness that suits the light you are actually in, and favor coverage over minimal frames if you spend time near water or snow. Every pair we make blocks 100% of UV and carries a lifetime replacement guarantee with a processing fee, so a good habit does not have to be an expensive one. Have a look through all of our collections or start with the bestselling frames if you would rather not sort through everything.