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UV Index
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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.
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