UV400 should be non-negotiable for any ski goggle purchase. It blocks 100% of UVA and UVB radiation up to 400nm wavelength, which is the full spectrum of harmful UV that reaches the earth's surface. At mountain altitudes, UV radiation is 30-40% stronger than at sea level, and snow reflects up to 80% of it back at you—essentially double-exposing your eyes.
Lower UV ratings like UV380 or basic UV coatings leave gaps in protection, particularly at the higher end of the UVA range. That might be okay for a quick afternoon at a small hill, but it's not worth the risk for a full day in the mountains. Basic UV coatings can also wear off over time, leaving you unprotected without realizing it.
The biggest myth is that dark lenses mean better UV protection—they don't. UV is invisible, and a clear UV400 lens protects far better than a dark lens without proper UV filtering. Always check for the UV400 label specifically.