November 23, 2021

UV Index Meaning: What Does UV Index Mean?

The UV Index measureshow much UV exposure is expected throughout a day. It is forecasted by the Environmental Protection Agency (EPA) and the National Weather Service (NWS) to give the public an idea of how damaging the sun will be during the day. The forecasted UV Index is usually reported  for the amount of UV radiation at solar noon, however, some organizations report it hourly. 

The UV Index was created to help reduce sun exposure for the public. Skin cancer is the most common type of cancer. It isoftencaused by overexposure to UV radiation whichresults in genetic defects in the skin.Educating someone about how much UV radiation they are going to get in a day,will give them a better idea of how to protect themselves. Thus the UV Index was born. 

How is the UV Index Calculated?

The UV index is calculated using NWS forecast models. To calculate the UV Index for any time of day, the NWS uses the total ozone amount, the sun's angle, the amount of clouds, the elevations, and the aerosol count. With all of these inputs, they get a refined UV Index number, where one UV Index unit is equivalent to 25 milliWatts per square meter. To make this easier for people to understand, the EPA and the NWS use the UV Index Scale.

What is the UV Index Scale?

The UV Index scale starts at 1 and goes to 11+. Each number is categorized into one of 5 levels: low, moderate, high, very high, and extreme. Formatting the scale this way, is much simpler than saying, "There is going to be 175 milliWatts per square meter in UV radiation today at solar noon, 125 milliWatts per square meter tomorrow, and 50 milliWatts per square meter Thursday!" The UV Index Scale is an easy to understand chart that allows people to know how much sun exposure they will get during the day, without all the fancy terminology.  

How To Read The UV Index?

In order to read the UV Index, you first need to know what the index value is for your location. Go to the EPA's website here or google "What's the UV Index for [your location]."  Both of these methods will give you a number on the UV Index Scale. To know what protection you need, find your value below and use the methods outlined in the paragraph beneath it:

UV Index 1 or 2

A UV Index of 1-2 is considered a low exposure category. If you burn easily, it is best you cover up and use sunscreen. On sunny days, it is best to wear sunglasses, especially if there is snow around. Snow has the ability to nearly double your UV exposure because of its reflective properties. So, even if the UV Index is low, you are still exposed to damaging UV radiation. Wear your Sunscreen!

UV Index 3 to 5

With a UV Index of 3, 4 or 5, you are going to want to take actions to protect your skin. These numbers are in the moderate exposure category. You should cover your skin and use sunscreen when going outside. During the midday hours, when the UV is the highest, you should stay in the shade. 

UV Index 6 to 7

At a UV Index of 6 or 7, you need to be taking serious sun protection precautions. Index values of 6 and 7 are classified as High exposure. Cover up, use sunscreen, and wear sunglasses. Limit your time in the sun between 11 a.m. and 4 p.m. when the sun is the strongest.

UV Index 8 to 10

A UV Index of 8 to 10represents ahighly dangerous amount of UV radiation. In this range, exposureis categorized asVery High. At these high levels of exposure, you can burn quickly under the sun. Avoid exposure to the sun during 11 a.m. and 4 p.m. If you can't, wear sunscreen, a hat, tightly knit clothing, sunglasses, and try to stay in the shade as much as possible.

UV Index of 11+

When you see a UV Index of 11+, you need to do all you can to protect yourself from the sun. If you don't protect your skin it could burn in minutes. At levels this high, you need to stay in the shade, cover your skin with clothes, wear sunglasses, and use sunscreen. Again, avoid sun exposure between 11 a.m. and 4 p.m. 

When is the UV Index the Highest?

The UV Index is generally highest during midday, when the sun is the highest in the sky. However, as we learned earlier UV index is calculated through a number of different factors including cloud coverage. So a UV Index could be higher in the morning if the weather changed throughout the day! For example, if the skies were clear during the morning hours and heavily overcast later in the day the UV Index could be higher in the morning versus midday.

Since the UV Index depends on the Sun's angle, UV Indices fluctuate with seasons. UV radiation is generally higher in the spring and summer and lower in the fall and winter. Regardless you should wear sunscreen year round! Why? UVA rays, which contribute to skin aging, are more consistent year round versus higher energy UVB rays. For more information on why you should wear sunscreen year round Read:Why You Still Need Sunscreen in the Fall and Winter.

How high does the UV Index go

How High Does the UV Index Go?

The highest rating on the UV Index is 11+,when sun exposure israted as extreme. Use a sunscreen labeled SPF 50, wear tightly knit clothing, a hat, sunglasses, and stay out of the sun as much as possible. If you want to learn more about SPF, check out our article What Does SPF Stand For: What is SPF?.

What UV Index Requires Sunscreen?

All UV Index values require sunscreen. No matter how low the rating, you are still exposing your skin to UV radiation that can cause premature aging, skin damage, and skin cancer. To get optimal protection from these damaging UV rays, you want a sunscreen with an SPF of at least 30 that is also labeled "Broad Spectrum". 

All of our sunscreens at TropicSport are Broad Spectrum, protecting your from both UVA and UVB radiation. They are chemical free and made with the only two ingredients labeled GRASE (Generally Recognized as Safe and Effective), Zinc Oxide and Titanium Dioxide. Unlike chemicals whichabsorb into your skin and bloodstream, our mineral sunscreen sits on top deflecting the UV radiation. With our products you can feel safe from the sun, without putting yourself and your environment in danger of chemical sunscreen. Check them out for yourself:

 

What is Broad Spectrum Sunscreen?

A Broad Spectrum sunscreen protects your skin from both UVB and UVA rays. If a sunscreen is not labeled "Broad Spectrum", then it only protects you from UVB rays. UVB rays have more energy than UVA rays and are the main reason you get sunburnt. UVA rays have less energy than UVB rays, butmake up 95% of the UV radiation that reaches earth. Exposure to UVA rays primarily causes skin cell aging and can indirectly damage the cell's DNA. When shopping for sunscreens be sure to look for that "Broad Spectrum" label!

 

Do Clouds Block UV Rays?

Another commonly asked question when discussing UV rays is, "Do Clouds Block UV Rays?" The answer is clouds do not block UV rays completely. In fact, in some cases clouds can enhance UV radiation because of scattering and reflection. For example, on average partly cloudy days have lower UV radiation, but under certain circumstances there can be more UV radiation than on a cloudless day! During fully overcast days, there is a reduction of UV radiation hitting the Earth's surface. However, UV rays still make it through.  That is why regardless of cloud coverage it is important to wear your sunscreen and protective clothing. You can get burned through clouds, no matter how thick. 

Luckily for you, the UV Index takes into account cloud coverage. If you are uncertain about how much sun protection you need for the day, check the UV Index for your location and use the guidelines above!

 

Jack Herrmann
Jack Herrmann


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