What is The UV Index? (Ultraviolet Index Explained)

The UV index was standardized in 1994 by the National Weather Service (NWS) and the U.S. Environmental Protection Agency (EPA).

What is the UV index?

The UV index is an open-ended linear scale which assists people in making informed decisions with regards to planning outdoor activities based on the intensity of the UV radiation on that specific day. The scale ranges from 1 (safe) to 11 (dangerous).

In this article we are going to explain the importance of the UV index and how you can use it to plan your outdoor activities safely, in accordance to the strength of the sun.

What is the UV index?

What is the uV index

The UV index was developed by Canadian scientists in 1992 and was later adopted and standardized in 1994 by the NWS and EPA.

  • Essentially, the UV index is an international measurement, that measures the potential sunburn causing Ultraviolet (UV) radiation at a specific location and time.

The UV index is usually intergrated into weather and temperature forecasts and is increasingly being made available as an hourly forecast as well.

Ultimately the point of the UV index is to help people protect themselves and their loved ones from high levels of UV radiation that can damage skin, eyes and cause other health related issues if exposed to in excess.

Read also: Solar Panels For Home Use (The Ultimate Guide)

What is a safe UV index?

0 – 2 or green on the UV index scale is regarded as safe levels ultraviolet radiation. On this level you can safely suntan or expose your skin directly to the sun with low probabilities of serious damage.

However, it is still recommended to cover up and protect your skin using broad spectrum SPF 30+ sunscreen, we usually recommend using reef safe suncreen like this one. Also, keep in mind that bright surfaces, like sand, water, and snow, exacerbate the UV exposure.

UV Index Scale Chart

UV indexGraphic colorRisk of harm for the average adultRecommended protection
0 to 2Green“Low”A reading of 0 to 2 symbolizes low danger from the sun’s UV rays. It recommended to wear polarized sunglasses on especially bright days. If you have very sensitive skin, make sure you cover up and use a broad spectrum SPF 30+ sunscreen.
3 to 5Yellow“Moderate”3 to 5 equates to a moderate risk of harm if you are exposed to the sun and unprotected. During midday the sun is at its strongest, stick to shade of possible. If you plan your activities outdoors on a 3-5 UV index day, always make sure to wear sun protective clothing such as UV blocking (polarized) sunglasses and a wide brimmed hat like this one. Even on cloudy days it is recommended you once again use reef safe sunscreen lotion at least SPF 30+.
6 to 7Orange“High”A reading of 6 to 7 means high risk of getting sun damage from unprotected exposure to the suns UV rays. Eye and skin protection is definitely needed. It is recommended that you avoid sun exposure between 10am and 4pm. If you must be outside always wear the necessary protective clothing already mentioned.
8 to 10Red“Very high”A UV index with a reading of 8 to 10 means you are at very high risk of being harmed from unprotected sun exposure. It is paramount that you avoid the sun between 10am and 4pm. If you must be outside make sure to use SPF 50+ reef safe sunscreen and various other sun-protective clothing
11+Violet“Extreme”A UV index reading of 11 is extreme and you should avoid sun exposure at all costs. If you must be exposed to the sun, make sure you take all the precautions possible as skin and eyes can burn within minutes of unprotected exposure.

Which country has the highest UV index?

Peak UV radiations occurs within the tropics (high sun, low ozone), at a high altitude site, most notably, in the Southern Hemisphere.

The country with the highest recorded UV index to date has been Cuzco, in southern Peru.

Additionally, further studies done by scientist Richard McKenzie, also found that many high Andes in Bolivia, Chile and Argentina regularly hit extreme UV index levels higher than 25.

Best apps and websites for monotoring the UV index

  1. EPA’s Sunwise
  2. Tantastic
  3. Wolfram Sun Exposure
  4. Ultraviolet UV index
  5. UV Lens
  6. EPA UV index website


Protecting yourself from harmful UV radiation is paramount to a healthy lifestyle. One can reduce risk of developing skin related diseases by informing themslves on what the UV index is and how they can use it to protect themselves. We hope this article served as resource to help you in your quest to understanding ultraviolet radiation a little better.


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