The sun sends out different types of radiation:
- sunlight (that you can see and feel as heat)
- infrared radiation (that you can feel as heat)
- UV radiation (that you cannot see or feel).
You need to be careful when it’s cool (and/or cloudy) outside from September to April. When it’s cool it means there’s less infrared radiation but not necessarily less UV radiation. You can still get sunburnt on cool and cloudy days.
Types of UV radiation
There are three types of UV radiation from the sun - UVA, UVB and UVC. All can cause skin and eye damage.
- UVA radiation goes deep into the skin. It can cause long-term damage like wrinkles, blotchiness, sagging and skin cancer
- UVB radiation gets into the top layer of skin and can cause sunburn, skin damage and skin cancer.
- The ozone in the atmosphere absorbs most UVB from reaching the earth's surface.
- UVC is the most dangerous type of UV radiation.
- Ozone and oxygen in the Earth’s atmosphere absorb all UVC so none reaches the earth's surface. However, there are other sources of UVC, such as in arc welding, which workers need to protect themselves from.
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 from September to April (the daylight saving months), when UV radiation levels are higher.
UV radiation is affected by:
- time of day
- time of year
- cloud cover
- reflection (for example, off snow and ice)
- closeness to the equator.
In New Zealand, always protect skin and eyes from September to April, when you're in the mountains, out on the water, or around snow and ice - Slip, Slop, Slap and Wrap.
NIWA provides UV index (UVI) forecasts throughout the year.
You can check UV data for your location using the free uv2Day app. This app provides UVI forecasts for locations in New Zealand, Australia and the South Pacific. It uses NIWA data.
For further information about UV (ultraviolet) radiation, and how it can affect health, take a look at the UV exposure indicators on the Massey University website.