NILU measures UV at three locations in Norway: Blindern, Andøya and Ny-Ålesund. We also measure ozone at these stations. The purpose of the dual measurements is to look at the variations in UV along with ozone changes, but there are also other factors that are important in determining levels of UV levels on the ground.

A thin cloud cover has a negligible effect on UV radiation, while a thick cloud cover can reduce UV radiation by up to 50%. In partly cloudy weather, the reflection from clouds can result in UV levels that are higher than if the sky is clear. Particles in the atmosphere are important in determining the amount of radiation reaching the ground. UV levels can be lowered by as much as 20% if particulates and pollution levels are high.

NILU’s UV research and monitoring are particularly focused on the health effects of UV, but also on the effects of particles on UV levels.

Everyone in Norway can check the uv.nilu.no webpage to get their local UV forecast and the best advice about sun exposure. Remember that clean new snow reflects up to 90% of UV radiation, while older snow reflects less. This means that in Norway at Easter time, if skies are clear, if there is new snow, or if Easter comes later in the spring, the sun can be as strong as the midsummer sun at sea level.


UV stands for ultraviolet radiation. The sun radiates several different types of radiation, including visible light, which is what we see, and UV radiation, which we do not. UV radiation is divided into three main types according to its wavelength:
  • UV-A has a wavelength of 315-400 nm (1 nanometre, nm, is a millionth of a millimetre), is not blocked by the ozone layer, and is considered less harmful than UV-B.
  • UV-B, with a wavelength of 280-315 nm, is generally largely taken up (absorbed) by the ozone layer. However, with the gradual thinning of the ozone layer, more and more of the UV radiation that reaches the Earth’s surface comes in the form of UV-B. A thinner ozone layer will lead to increased UV damage to plants and animals. The degree of UV-B damage depends on how much atmospheric ozone remains to act as a filter, the sun’s angle in the sky, and clouds, which also protect the Earth from a portion of ultraviolet radiation.
  • UV-C, with a wavelength of 200-280 nm, is lethal. Fortunately, UV-C is completely absorbed by stratospheric ozone and oxygen. Even if the ozone layer has been strongly depleted, UV-C cannot not penetrate the atmosphere.