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The UV Index

UV INDEX MAPS

  • Europe Alpine Profile 
  • Mediterranean Region 
  • Africa 
  • Asia 
  • South America

 

The UV Index is a device that is used to measure the amount of the Sun’s ultraviolet (UV) radiation that will reach the Earth’s surface during the peak hour of sunlight (1:00 PM local daylight savings time). It is intended to give people a good idea of the risk of being exposed to the Sun and to aid in planning one’s day so that one is not over-exposed to the Sun’s UV rays.  


The UV Index was recently introduced following the concerns of the effects of UV Radiation. Too much exposure to UV Radiation can cause immediate problems such as sunburn blistering, but also more concerning long term problems such as skin cancer, cataracts and premature ageing (see Health section for more information). 


In the past few years, there has been much greater public awareness of the effects of UV Radiation and educational campaigns have been launched by international bodies such as the World Health Organisation, who first introduced the Index in the United States of America. The UV Index is now used in many other countries around the world, where UV Radiation is considered to be a risk. 

What is the UV Index?

The Index is a number rating from 0 to 10+ which gives a measure of the amount of UV Radiation that will reach the Earth’s surface during the peak hour of sunlight, when there is the greatest amount of UV rays entering the Earth’s atmosphere. The table below summarises the rating: 

 

Index Value    Exposure   
0 to 2 Minimal
3 to 4 Low
5 to 6 Moderate
7 to 9 High
10 or above Very High

 

 

 

 

 

or an Index Value of 1 to 2, most people should be able to stay in the sun during the peak hour of sunlight. Although there is a low risk for a value of 3 to 4, people with fair skin can burn in 20 minutes. A Sun Protection Factor (SPF) cream of at least 15 should be used. (please add link to SPF) 
A value of 5 to 6 means moderate risk of harm from unprotected Sun exposure. Fair skinned people may burn in 15 minutes. Again, an SPF of 15 or more should be used. A value of 7 to 9 indicates a high risk of harm from unprotected Sun exposure. Fair skinned people may burn in as little as 5 minutes and caution should be taken, avoiding long periods in the sun, especially between 10am and 4pm. 

A value of 10 or above means a very high risk. Extreme caution should be taken, especially for those with fair skin that burns easily. A sunscreen should be applied every 2 hours or sun protective clothing and hats should be worn both when exposed to the Sun and when in shaded areas. 

There are various factors which affect the amount of UV Radiation entering the atmosphere as well as the UV Index rating, these are: 

 

  • air pollution (which reduces UV radiation) 
  • altitude 
  • latitude (positioning of the sun in the sky) 
  • distance from the equator 

(for more information on these factors, see UV Radiation section). 

However, another important factor affecting the amount of UV radiation one is exposed to, is skin colour. The table below summarises the risk for different skin colours:
Skin Colour 

Index Fair (burns)    Fair (tans)    Brown Black
1 to 2 Low Low Low Low
2 to 4    Medium Low Low Low
5 High Medium Low Low
6 Very High Medium Medium    Low
7 Very High High Medium Medium   
8 Very High High Medium
Medium
9 Very High High Medium Medium
10 Very High High High Medium

 

 

 

 

 

 

 

 

In most countries, the UV Index is only published in the summer season when there is a substantial level of UV Radiation. The usual time of publication is with TV weather reports. 

 

Where can I get a UV Index rating for where I live?
Daily updates of UV levels can be found on a number of web sites on the Internet, but it is also now more common for a daily update to be presented via other media such as television and radio along with weather and environmental information. Portable pocket-sized UV Radiation meters also give ratings. [link to online shop or link to site selling these meters - to be advised]. 

 

Check the current UV Index ratings for USA, United Kingdom. 

For more information on this subject: 

Climate Prediction Center - a comprehensive site with links to many international uv index sites.
The Environment Protection Agency
The Weather Channel