If you pay attention to the news during the summer, you’ve read about the UV index. So, what does it mean in simple terms?
The UV index is a calculation derived by the National Weather Service (NWS) and the Environmental Protection Agency (EPA) to tell us how much damaging ultraviolet (UV) light from the sun to expect on any given day. The UV index ranges from a low of 1 to a high even over 11. The EPA has a website that forecasts the UV index for every zip code every day at www.epa.gov/sunwise/uvindex.html.
The UV index is calculated on the amount of cloud cover, the amount of ozone in the atmosphere, and the altitude of the zip code you are interested in. When there are no clouds, all of the UV rays from the sun are coming through. But, even with cloud cover, over 31 percent of UV rays still penetrate.
The UV index also takes into consideration the amount of ozone in the atmosphere. When there is more ozone in the atmosphere, fewer UV rays come through. When there is less ozone in the atmosphere, more UV rays come through. The ozone neutralizes and absorbs harmful UV light. Now you can see one reason why a hole in the ozone layer can be problematic.
For mountain climbers and skiers, for every three thousand feet above sea level you are, the strength of UV rays increases 6 percent.
When you see a report that the UV index is in the low ranges of 1 to 4, do not be lulled into a false sense of security. Even with a UV index of 1 or 2, you still need to use sunscreen every time you are out in the sunlight. The minimum SPF you should be using is 15. Damage to the skin from UV exposure is from an accumulation of the harmful effects of UV rays. You need to be protected as often as possible.
Following the UV index on the EPA’s website or from other news outlets is an excellent daily reminder to apply sunscreen.