What is the UV Index?
UV Index & Sun Protection
Origins of the UV Index
What Determines UV Strength?
Latitude & Time of Year
Time of Day
Reflection off Water
Reflection off Snow
Clear Skies & Clouds
UV Exposure & Your Health
Immune System Suppression
What is UV?
UV is short for 'Ultraviolet Radiation' and is part of the electromagnetic radiation, or simply energy, we receive from the Sun. No matter where we are in the World as long as there is sunshine we are being exposed to some level of UV radiation. However, UV strength and your risk of exposure varies greatly depending on a number of things such as your location, the time of year and time of day, altitude, cloud cover, ozone levels, and more (see what determines UV Strength). The level of UV and your risk of exposure is represented by the UV Index, and you can find what the UV Index is for your location using our hourly UV forecast.
Over exposure to UV can have serious health consequences such as skin cancer (both non-malignant and malignant melanoma), premature aging of the skin, cataracts, eye cancer, snow blindness, and immune system suppression. Whilst much attention is given to melanoma, one should be aware of the other risks involved.
Ultraviolet radiation is a form of light that is not visible to humans. It is called ultra (beyond) violet because it is beyond the frequency which humans identify as the colour violet. Although we cannot see this type of light, other life on Earth such as bees and butterflies can, and use it for guidance and identification. UV is divided into three categories UVA, UVB, and UVC, depending on it's wavelength. Each type can be damaging to health in different ways.
At the surface of the Earth roughly 95% of solar UV radiation is comprised of UVA, which has a wavelength of 315-400 nm. UVA penetrates deeper into the skin than UVB, and exposure to high doses of UVA can cause indirect DNA damage, age your skin, cause skin cancer and damages your eyes. UVA does not cause sunburn, and since SPF only indicates a level of protection against sunburn, it is important to use broad spectrum sun lotions, which will offer protection against both UVA and UVB.
Sunbeds give off mainly UVA radiation, and have been classified as carcinogenic in some countries, with minors being banned from using them.
UVB radiation does not enter as deeply into the skin as UVA, and is mostly absorbed by the outermost layer of the skin (the epidermis). UVB is more likely to cause sunburns and is primarily responsible for causing skin cancer. UVB is associated with the development of malignant melanoma, which can be fatal if left undiagnosed and untreated.
Approximately 90% of UVB radiation is absorbed by ozone, water vapor, oxygen and carbon dioxide. However, as ozone is the main absorber of UVB radiation, the UVB intensity at the Earths surface depends strongly on the total amount of ozone in the atmosphere, and thus on the thickness of the ozone layer. UVB has a wavelength between 280-315 nm.
UVC is the most damaging of all three types of UV radiation but is removed by the ozone layer, so it does not reach the Earth's surface. However, continued damage to the ozone layer by CFCs (chlorofluorocarbons) and halon gases may allow UVC radiation to reach the Earths surface.
This is a a potential problem in Australia as the Ozone layer there can be relatively thin. UVC has a wavelength between 100-280 nm.