Ultraviolet solar radiation is involved in many biochemical processes, in the case of human beings in the production of vitamin D and melanin, but overexposure may result in highly harmful effects, such as erythema, sunburn and even skin cancer. This way, it comes to be of great importance to know the intensity of the radiation in a determined instant in order to choose the right protection and avoid the exposure in those moments when it may result more harmful. Skin cancer is caused primarily by exposure to ultraviolet (UV) radiation.

The UV radiation is not uniform in a medium size territory. It varies depending on:

  • Sun elevation: the higher the sun in the sky, the higher the UV radiation level.
  • Latitude: the closer to the equator, the higher the UV radiation levels.
  • Cloud cover: UV radiation levels are highest under cloudless skies but even with cloud cover, they can be high.
  • Altitude: UV levels increase by about 5% with every 1000 metres altitude.
  • Ozone Layer: ozone absorbs some of the UV radiation from the sun. As the ozone layer is depleted, more UV radiation reaches the Earth’s surface.
  • Ground reflection: many surfaces reflect the sun’s rays and add to the overall UV exposure (e.g. grass, soil and water reflect less than 10% of UV radiation; fresh snow reflects up to 80%; dry beach sand reflects 15%, and sea foam reflects 25%).

UV radiation is composed of three different types, depending on its wavelength: C-ultraviolet radiation (CUV), in the range between 100nm and 280nm, B-ultraviolet radiation (BUV), between 280nm and 315nm, and A-ultraviolet radiation (AUV), between 315nm and 400nm. The shorter the wavelength, the more harmful it is, but also the atmospheric attenuation is higher. Thus, CUV is the most noxious of the three, but it hardly arrives at the Earth’s surface, while AUV, which reaches the soil with more intensity, has a much lower effect. In practice, BUV is the most dangerous.

Ultraviolet Solar Radiation Levels IndexThe Ultraviolet Index (UVI) is the international standard for UV measurement, developed by WHO, the United Nations Environment Program and the World Meteorological Organization. It is designed to indicate the potential for adverse health effects and to encourage people to protect themselves. The higher the UVI value, the greater the potential for damage to the skin and eye, and the less time it takes for harm to occur. Sun protection should be used when the UV index reaches 3 or above.