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To be considered safe, sunglasses must block 99% to 100% of both UVA and UVB radiation. This is often labeled as "UV400" protection. The "400" refers to the wavelength of light measured in nanometers. By blocking all light rays with wavelengths up to 400 nanometers, these lenses prevent the most damaging invisible energy from penetrating the eye structure.
read more about sunglasses uv blockage ...A common misconception is that darker lenses provide better protection. This is false. Lens tint only reduces visible light (brightness), not UV radiation. In fact, wearing dark glasses without UV filters is more dangerous than wearing no glasses at all. The dark tint causes your pupils to dilate (open wider). If the lens does not block UV rays, this dilation allows a much larger amount of radiation to enter the eye than if you were squinting in bright light.
The sun emits different types of ultraviolet rays. UVB rays (280-315 nm) are the primary cause of sunburn and surface damage like photokeratitis (snow blindness). UVA rays (315-400 nm) penetrate deeper into the eye, contributing to cataracts and macular degeneration. A proper UV400 lens blocks both types completely. Standard clear polycarbonate lenses naturally block most UV, but specific coatings are needed to reach the full 100% threshold.
Even with perfect lenses, UV radiation can bypass the frame. Data shows that up to 20% of UV light reaching the eye comes from the sides, top, or bottom of the frame. This is called "peripheral light leakage." Because of this, large, wraparound styles are statistically safer than small, flat frames because they physically block the light from entering around the edges.
Price is not a reliable indicator of UV safety. Studies testing random samples of sunglasses found that cheap drug-store glasses often perform just as well as designer frames. Many inexpensive glasses are made of polycarbonate, a material that naturally blocks UV without needing expensive additives. The extra cost of designer glasses pays for the brand name, frame materials, and optical clarity, not necessarily better UV blockage.
No. Polarization blocks glare (reflected light), not UV rays. While most polarized lenses are also made to be UV400, the polarization filter itself does not stop ultraviolet radiation.
Generally, no. The UV blocking properties are usually built into the lens material (like polycarbonate) rather than sprayed on. Unless the lens is physically broken or extremely old and degraded, the protection remains stable.
Most do. High-index and polycarbonate prescription lenses have built-in UV protection. Older plastic (CR-39) lenses may need a specific UV coating added by the lab to reach 100% blockage.
If you are unsure if your old sunglasses are still safe, take them to an optical shop. Most opticians have a device called a UV photometer (or UV meter). They can slide your glasses into the machine and tell you the exact percentage of UV rays passing through the lens in just a few seconds.