National Sunglasses Day – held annually on June 27 – is The Vision Council's campaign to raise awareness of the importance of wearing sunglasses to protect the eyes from the sun's ultraviolet (UV) rays.
Ultraviolet radiation can penetrate Earth’s atmosphere at any time and place, but certain regions have heightened radiation levels. UV rays are particularly strong near the equator, since they travel a shorter distance to reach Earth’s surface. Cities at high altitudes also share higher UV levels because the sun’s rays can easily penetrate the thin atmosphere.
To determine areas of high risk, The Vision Council analyzed national UV index levels from the U.S. Environmental Protection Agency (EPA) and the National Weather Service (NWS). More than 50 cities were evaluated for solar radiation strength, season, climatic conditions, ozone concentration, cloudiness and elevation. Below is a map showing the top 25 U.S. cities receiving the highest levels of UV exposure.