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11. UV Index
a) Effect of UV Radiation
In addition to visible light, the sun also emits other forms of light radiation which are not visible to the human eye. While
visible light has a wavelength of around 400-760nm, UV light lies below that at 100-380 nm. The following is applicable:
The shorter the wavelength, the stronger the damaging effect of UV radiation on the skin.
UV radiation is divided into three different categories:
• UV-A (315-380nm)
This form of UV (about 95%of total UV radiation that reaches the earth's surface) leads to immediate tanning which only
last a short period of time. No sunburn actually occurs, no protective layer is produced in the skin. As UV-A radiation
penetrates very deeply into the skin tissue, it leads to skin aging and the appearance of wrinkles. Sensitive skin can
exhibit rashes or similar: in the longer term the risk of skin cancer is increased.
• UV-B (280-315nm)
The remainder of the UV radiation which reaches the surface of the earth (approx. 5%) causes slow but long lasting
tanning of the skin. The skin produces a protective layer. UV-B radiation causes sunburn quickly, and sunburn can have
longer term effects such as skin cancer.
• UV-C (100-280nm)
Shortwave radiation does not reach the surface of the earth, as it is absorbed by the atmosphere.
The effects of UV radiation on the skin depends on many different factors. These include not only the period
of exposure and the skin type, but also factors like the cloud cover, the position of the sun (e.g. midday), the
season, the elevation, the surroundings (reflections and/or diffusion on water, sand or snow increase the
effect), the clothing used and any sunscreen which may have been used.
