​Understanding UV and VLT

UV Protection

Ultra

violet (UV) rays from the sun can damage your eyes by contributing to cataracts, macular degeneration and growths on the eye, including cancer. All of the sunglasses offered at REI block 100% of UV light.

UVB rays are the main concern for eyes. According to the American Academy of Ophthalmology, "Long-term exposure to ultraviolet (UV) radiation in sunlight is linked to eye disease. UVB radiation is considered more dangerous to eyes and skin than UVA radiation."

UVA rays are the primary ones absorbed by your eyes. While they pose far less concern than UVB, doctors still recommend that they be avoided.

UVC rays are not a concern, as they are blocked by the atmosphere.

UV protection information should be printed on the hangtag or price sticker of any sunglasses you buy, no matter where you buy them. If it isn't, find a different pair. Also keep in mind that cheap, tinted sunglasses with limited UV protection can actually do more harm than good, as they cause your eye lenses to open up wider, leaving them even more vulnerable to UV rays. Kids' eyes are especially vulnerable to UV light, since they don't have the same level of natural protection as adults.

Visible Light Transmission

The amount of light that reaches your eyes through your lenses is called Visible Light Transmission (VLT). Measured as a percentage, VLT is affected by the color and thickness of your lenses, the material they're made of and the coatings they have on them.

All-purpose sunglasses have a VLT of around 15-25%. Aim for glasses in this range if you need a pair for everyday use and basic recreational activities.

Glacier glasses (special sunglasses designed specifically to protect your eyes from the intense light at high altitudes) have a VLT of around 4-10%. Most glacier glasses also have shields to protect your eyes from light coming in from the sides of your lenses. Because of their low light transmission, glacier glasses should not be used for driving or other everyday activities.

Photochromic lenses automatically adjust to changing light intensities to protect you in a wider range of conditions. These lenses actually get darker (to block more light) on bright days, and lighter when conditions get darker. A couple of caveats: The photochromic process takes longer to work in cold conditions, and it doesn't work at all when driving a car (UVB rays do not penetrate your windshield, so the process is moot).