What is UV400?
Sunglasses labeled UV 400 provide nearly 100% protection from harmful ultraviolet light rays, blocking wavelengths up to 400 nanometers, including UVA and UVB rays.
Ultraviolet, or UV, rays are electromagnetic radiation from the sun. While you can’t see it, UV light penetrates Earth’s atmosphere and reaches your skin and eyes in the form of UVA and UVB waves. Protection from UV light is important because without it you’re at risk of developing cataracts, macular degeneration, photokeratitis (also known as snow blindness) or even eye cancers that can lead to permanent blindness.
Note that not all sunglasses are considered UV-protection sunglasses. A pair of sunglasses may have dark lenses, which could be presumed to block rays, but that doesn’t mean the shades provide adequate UV protection.
If those sunglasses with dark lenses don’t include UV protection, those darker shades are actually worse for your eyes than not wearing any protective eyewear at all. Why? Because the dark tint can cause your pupils to dilate, exposing your eyes to more UV light.