The end of April means it’s that time of year again when you need to have sunscreen, sunglasses, and a hat handy due to UV radiation from the sun. These items will work to protect your skin and eyes from solar radiation damage.

The risk of overexposure to the sun’s UV radiation is forecasted daily with a value called the UV Index, ranging from 0 (“Low”) to 11+ (“Extremely High”).

UV Index factors

Factors determining UV Index values

During the summer months, the UV Index in the Tennessee Valley is most often 8, 9, or 10 in the “Very High” category.

The UV Index is calculated and dependent on several factors:

  1. Time of day: Solar UV radiation is greatest at midday from 10am to 4pm, especially 11am to 3pm Daylight Saving Time.
  2. Time of year: The UV Index peaks in the summer on either side of the summer solstice in June.
  3. Cloud cover: A clear sky allows the highest amount of UV radiation to make it to the surface, but even on cloudy days, some radiation can penetrate all the way through the atmosphere.
  4. Latitude: Radiation is greatest at the equator due to the most direct rays from the sun. The Tennessee Valley is in the mid-latitudes, so less radiation than the equator but more than areas farther to the north.
  5. Altitude: Higher elevations will have greater UV radiation, and thus, a higher index value.
  6. Reflectivity of surfaces: Water, sand, and snow will all reflect the sun’s rays, increasing your risk for overexposure.
  7. Stratospheric ozone: Ozone is our friend. The layer of ozone high up in the atmosphere absorbs shorter wavelengths of UV radiation from the sun. The more stratospheric ozone present, the less radiation makes it to the surface, helping to reduce the UV Index.
Monthly UV Index

Note, none of the above factors is temperature dependent. Your sun safety practices on a cool, sunny April day should be the same as a hot, steamy August day.

Play it safe over the next few months by using a hat, sunglasses, protective clothing, sunscreen at SPF 30+, seeking shade, and limiting outdoor time during midday.

These proactive steps will help your skin and eye health.

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