Understanding UV Radiation

The sun sends out different types of radiation – visible light that we see as sunlight, infrared radiation which we feel as heat and UV radiation that we can't see or feel. 

People often confuse infrared radiation and UV radiation. When the temperature is cool it means less infrared radiation but not necessarily less UV radiation.

Types of UV radiation

There are three types of UV radiation, categorised by wavelength: UVA (the longest wavelength of the three), UVB  and UVC. 

  • UVA (aging) can can damage our skin's cells, and cause skin cancer.
  • UVB (burning) can cause sunburn, skin damage and skin cancer. The ozone in the atmosphere absorbs most UVB from reaching the earth's surface. Exposure to low wavelengths in the UVB range are required for vitamin D production.
  • UVC is the most dangerous type of UV radiation. Ozone absorbs all UVC so none reaches the earth's surface.  However there are artificial sources of UVC such as in arc welding which workers need to protect themselves from.

Factors affecting levels of UV radiation

Levels of UV radiation from the sun are always changing.  In general, in New Zealand, UV radiation is damaging to skin and eyes over the daylight saving months - September to April, when UV radiation levels increase.  From September to April, the Sun Protection Alert tells you the time each day when you need to protect your skin and eyes from the hazard of UV radiation. 

The total amount of UV radiation present at a given location is affected by many factors including: 

  • closeness to the equator
  • time of day
  • time of year
  • cloud cover
  • altitude
  • scattering
  • reflection.

Remember to always protect skin and eyes when you're in the mountains, around snow,  ice and water, when UV levels are damaging.

Read more about UV radiation at NIWAs website.  Their UV index forecast is here.  You can access a free android or i-phone UV index app, called uv2Day which uses data from NIWA.