Your sunglasses should block 99% to 100% of both UVA and UVB radiation. The easiest way to confirm this is to look for a “UV400” label, which means the lenses filter all ultraviolet light up to 400 nanometers, covering the full spectrum of rays that can damage your eyes. Anything less leaves a gap.
Why UV400 Matters More Than “UV Protection”
Ultraviolet light sits on a spectrum. UVB rays fall between 280 and 315 nanometers, and UVA rays extend from 315 to 400 nanometers. Many cheaper sunglasses block UVB effectively but cut off protection around 380 nanometers. At that cutoff, roughly 20% of damaging UVA rays still pass through the lens and reach your eyes. UV400 lenses close that gap entirely, filtering 100% of both UVA and UVB radiation.
When you’re shopping, look for one of these on the label or product listing:
- UV400: Blocks all UV light up to 400 nm.
- 100% UV protection: Equivalent to UV400, though phrased differently by some brands.
- 99–100% UVA/UVB protection: The minimum recommendation from eye health organizations.
If a pair of sunglasses simply says “UV protection” without specifying a percentage or the UV400 standard, there’s no guarantee they block the full spectrum. Generic labels like “blocks harmful UV” are essentially meaningless without a number behind them.
What UV Rays Actually Do to Your Eyes
UV radiation damages the surface tissues of the eye, the cornea, and the lens. Short-term overexposure causes photokeratitis, essentially a sunburn on the eye. You might know it as snow blindness, which happens when UV reflects off snow, ice, sand, or water and overwhelms unprotected eyes. It’s painful but temporary.
The long-term risks are more serious. Cumulative UV exposure raises your risk of cataracts, eye cancers, and abnormal growths on the surface of the eye. These conditions develop over years, which means the damage is invisible until it isn’t. This is why consistent protection matters even on overcast days or during quick outdoor errands, not just at the beach.
Lens Tint Categories Explained
Darkness and UV protection are two separate things. A dark lens without proper UV filtering is actually worse than no sunglasses at all, because the tint causes your pupils to dilate, letting in more unfiltered UV radiation. That said, lens darkness does matter for comfort and visibility in different light conditions.
The international standard for sunglasses (ISO 12312-1) defines five filter categories based on how much visible light passes through:
- Category 0: More than 80% of light passes through. Essentially clear lenses, useful only for cosmetic eyewear with UV coating.
- Category 1: 43–80% light transmission. Light tint for overcast days or low-sun conditions.
- Category 2: 18–43% light transmission. Medium tint, good for moderate sunshine.
- Category 3: 8–18% light transmission. The most common category for general outdoor use in bright sunlight.
- Category 4: 3–8% light transmission. Very dark, designed for extreme glare environments like high-altitude mountaineering or glaciers. Not safe for driving.
For everyday use, category 2 or 3 lenses with UV400 protection will cover most situations. The key point: always verify UV protection separately from the tint level, because the darkness of the lens tells you nothing about how much UV it blocks.
Polarized Does Not Mean UV-Protected
This is one of the most common misconceptions. Polarized lenses reduce glare by filtering light that bounces off flat surfaces like water, roads, and car hoods. They make it easier to see in bright conditions, and they’re great for driving or fishing. But polarization is a glare filter, not a UV filter. The two serve completely different functions.
Not all polarized sunglasses offer UV protection. You can buy a polarized pair that cuts glare beautifully while still allowing UV radiation to reach your eyes. If you want both (and you should), check for polarization and UV400 as separate features on the label. Many quality polarized sunglasses do include full UV protection, but never assume it’s there just because the lenses reduce glare.
Lens Material Makes a Difference
Some lens materials block UV inherently, while others need a coating applied to the surface.
Polycarbonate is the standout. The polymer itself naturally absorbs ultraviolet light, so even a clear, uncoated polycarbonate lens blocks over 99% of UV rays. This protection is built into the material’s molecular structure, not a surface film that can scratch away or degrade over time. It’s also lightweight and impact-resistant, which is why polycarbonate is so widely used in both sunglasses and safety eyewear.
Standard plastic lenses (known in the industry as CR-39) do not block UV on their own. They require a separate UV-blocking coating to offer any meaningful protection. Glass lenses perform poorly against UV as well and also need a coating. High-index plastic lenses, the thinner ones used for strong prescriptions, vary by formulation and often require a coating too.
If you’re choosing between materials, polycarbonate gives you built-in UV protection as a baseline. For any other material, you’ll need to confirm that a UV-blocking coating has been applied.
How to Check Your Current Sunglasses
If you already own sunglasses and aren’t sure about their UV rating, many optical shops and optometrist offices have a UV light meter that can test your lenses in seconds. It’s usually free or very inexpensive, and it gives you a definitive answer rather than relying on a sticker that may have fallen off years ago.
Price is not a reliable indicator of protection. Inexpensive sunglasses from a reputable brand that lists UV400 on the label will protect your eyes just as well as a designer pair. What matters is the UV specification, not the price tag. A $15 pair with verified UV400 lenses outperforms a $200 pair with no UV rating every time.