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UV Index

UV Index

The UV Index describes the level of solar radiation on the earth's surface and is an indicator of the potential for damage to the skin and eyes.

The UV Index is important because the higher the index value, the greater the potential for damage to the skin and eye, and the less time it takes for harm to occur.

The UVI was developed through international effort by the World Health Organization ( WHO) in collaboration with the United Nations Environment Programme (UNEP), the World Meteorological Organization ( WMO), the International Commission on NonIonizing Radiation Protection (ICNIRP) and the German Federal Office for Radiation Protection (Bundesamt für Strahlenschutz, BfS).

What is ultraviolet radiation?

Ultraviolet radiation is a band of the electromagnetic spectrum that falls between visible radiation light and X-rays; towards the higher end of the spectrum it covers the wavelength range 100-400 nm and is divided into three bands:

UVA (315-400 nm)
UVB (280-315 nm)
UVC (100-280 nm)

As sunlight passes through the atmosphere, all UVC and approximately 90% of UVB radiation is absorbed by ozone, water vapour, oxygen and carbon dioxide.
UVA radiation is less affected by the atmosphere. Therefore, the UV radiation reaching the earth's surface is largely composed by UVA with a small UVB component; small amounts of this UV radiation are beneficial for people and essential in the production of vitamin D.

UVA radiation is less harmful than UVB radiation: the best known acute effect of excessive UVA radiation exposure is erythema, the familiar skin reddening termed sunburn while the effects of UVB radiation are inflammatory eye reactions such as photocongjunctivitis, cataract development, skin aging or melanomas, in the worst cases.

It is important to underline that while the risks for eye damage is dependent on the level of exposure, the risk for skin damage depends on the skin phototype.

What is a phototype?

Skin phototypes measure the reaction of the skin to ultraviolet radiation exposure and the consequent degree of tanning.
The skin phototype is determined by the amount of melanin in the skin. It is possible to discern four phototypes; those who have skin phototypes of I, II, or III values should make use of higher protection factors.