UV

Ultraviolet index l ultraviolet radiation

Ultraviolet index (UVI)

The Ultraviolet Index (UVI) is an international, scientific measure of the level of ultraviolet radiation (UVR) reaching the Earth's surface. It measures the intensity of UVR in our environment.  The higher the number the more intense the UVR and the greater the need for sun protection.

 UV Index

The UVI is promoted by the World Health Organization.  It is scientifically based, and is used internationally. “A Practical Guide' can be downloaded from http://www.who.int/uv/publications/globalindex/en/.

pdfUVI Index Board

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Ultraviolet radiation(UVR) 

What does UVR do?

Ultraviolet radiation (UVR) causes damage to our skin and can lead to skin cancer, which kills almost 300 New Zealanders a year. 

The major cause of skin cancer is over exposure to UVR from the sun, particularly during childhood and adolescence. Even if exposure does not cause obvious sunburn, damage still occurs and accumulates of the years.

Skin cancer can be prevented in most cases.  When the UVI is at 3 or more we need to protect ourselves. This happens almost daily between October and March, and can happen in winter, especially at high altitudes and in snow. Even when the temperature is not hot the UVR levels can be dangerous so temperature is not a good indicator of the need to protect yourself. UVR can penetrate light cloud cover, so even on cloudy days, and days that may have intermittent showers, you may still be at risk.

  • UVR cannot be seen or felt and the intensity of such radiation is not related to air temperature. 
  • People often get sunburnt on a cooler day because they tend to stay outside longer rather than seeking shade or covering up as on a hot day.

UVR levels

In New Zealand UVR levels vary throughout the day.  The UVR peaks at around solar noon (1.00 pm to 1.30 pm during the daylight saving months).

  • NZ has high UVR levels primarily because of the cleanliness of New Zealand’s air
  • The 'ozone hole' that occurs over the Antarctic continent during the spring of each year never extends over New Zealand.
  • The 'ozone hole' breaks up over the Antarctic each year in late summer. This is when 'pockets' of ozone-depleted air 'drift' over NZ. Approximately 50% of depleted ozone over NZ is from Antarctica
  • Example of UVR levels on a summer's day.  
  • UVR levels in New Zealand 

  • Find the UV level for your area:

    • NIWA website - click on your town/city and find out the time during the day you need to protect yourself from the sun.  The diagrams show UV levels at specific times of the day and give a maximum UV level for sunny and cloudy skies. 
    • SunSmart website - provides a map of New Zealand.  Click on your town/city for the forecast of maximum UVI and then your personal behaviour recommendations.

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