Ultraviolet radiation

What is ultraviolet radiation?

The sun gives out ultraviolet (UV) radiation, as well as visible light and heat. UV radiation and heat from the sun are not the same things. Many people mistake temperature as an indicator of the level of UV radiation. Even when the temperature is not hot, the UV radiation levels can be high enough to cause sunburn - so temperature is not a good indicator of when you need to protect yourself from the sun’s UV radiation.

There are both risks and benefits of exposure to UV radiation, so a balance is required to avoid the risk of skin cancer and at the same time to maintain adequate vitamin D levels.

So when is it safe to be outside?

During daylight saving months (September to April), the most suitable times to be outside without the need for sun protection is early morning (before 11 am) or later in the afternoon (after 4 pm), as these are the times when the UV radiation levels are low.

Winter UV levels

During winter the UV levels are usually low and so it is safe to be outside without sun protection most times. But UV radiation can be very high around snow or at high altitudes, so sun protection is necessary.

Sunbeds or Solariums

Tanning devices such as sun beds, booths and lamps (also known as Solarium) produce much higher concentrations of UV radiation than the sun, up to five times as strong as the midday summer sun. As UV radiation plays an important role in the development of skin cancer, it is important to be aware of the risks around exposure to these devices. More information about the risks of using sun beds can be found in the section sun beds and tanning. The Cancer Society website has an information sheet which outlines the risks associated with sun beds.

What influences the level of UV radiation?

UV radiation levels vary around the globe and over different seasons and times of the day. The level or amount of UV radiation in our environment is influenced by:

  • The sun’s elevation – the higher the sun in the sky, the higher the UV radiation levels.
  • Latitude – the closer to the equator you are, the higher the UV radiation levels.
  • Cloud cover – UV radiation levels can still be high with light cloud cover.
  • Altitude – the higher the altitude you are, the higher the UV radiation levels.
  • Ozone – the lower the ozone levels, the higher the UV radiation levels. Ozone absorbs some of the UV radiation. Ozone levels vary over the year and even across the day.
  • Ground reflection – some surfaces are more reflective eg, snow, sand and water, and reflect UV radiation into.

New Zealand’s UV radiation

Peak UV radiation levels in New Zealand are around 40% higher than those in North America. New Zealand’s exposure to high levels of UV radiation is mainly because of the position of the sun, the closeness of the sun during summer months, and our unpolluted skies. The depletion of the ozone layer has further increased our exposure to UV radiation. The Antarctic ozone layer hole usually breaks up in early summer. This means that, at times, New Zealand is affected by ozone-depleted air travelling over the country. For more information on ozone visit NIWA and the Ministry for the Environment.

What is the UV Index?

The ultraviolet radiation index (UVI) is a measure of the intensity of UV radiation in our environment, and is represented by numerical value. A higher UVI number means there is more UV radiation in the environment. When the UVI is at 3 or higher, we all need to protect ourselves and Slip, Slop, Slap and Wrap. This happens almost daily from September to April. During this period, throughout the day, UV radiation behaves in a predictable way. It is very high at about 1.00pm between September and April.

The UVI can also be high in winter, especially at high altitudes and in snow – so remember to protect yourself when you go skiing or snowboarding.

Find out the UVI in your area and get your own personal recommendations for UVR protection – this is the icon on the front page. These pages have to be retained as they are onto a separate link page.


Slip, slop, slap and wrap to be safe in the sun