The UV index is an international standard measurement of how strong
the ultraviolet (UV) radiation is from the sun
UV Index
|
Description
|
Recommended Protection
|
|
1-2
|
No danger to the average person
|
Wear sunglasses on bright days; use sunscreen if there is snow
on the ground, which reflects UV radiation, or if you have particularly
fair skin.
|
|
3-5
|
Little risk of harm from unprotected sun exposure
|
Wear sunglasses and use sunscreen, cover the body with clothing
and a hat, and seek shade around midday when the sun is most intense.
|
|
6-7
|
High risk of harm from unprotected sun exposure
|
Wear sunglasses and use sunscreen having SPF 15 or higher, cover
the body with sun protective clothing and a wide-brim hat, and reduce time
in the sun from two hours before to three hours after solar noon (roughly
10:00 AM to 4:00 PM during summer in zones that observe daylight saving
time).
|
|
8-10
|
Very high risk of harm from unprotected sun exposure
|
Wear sunscreen, a shirt, sunglasses, and a hat. Do not stay out
in the sun for too long.
|
|
11+
|
Extreme risk of harm from unprotected sun exposure
|
Take all precautions, including: wear sunglasses and use sunscreen,
cover the body with a long-sleeve shirt and trousers, wear a very broad
hat, and avoid the sun from two hours before to three hours after solar
noon.
|
|
A solar radiation sensor measures solar energy from the sun.
Solar radiation is radiant energy emitted by the sun from a nuclear
fusion reaction that creates electromagnetic energy
The units of measure are Watts per square meter.
Outside the earth's atmosphere, solar radiation has an intensity of
approximately 1370 watts/meter². This is the value at mean earth-sun
distance at the top of the atmosphere and is referred to as the Solar Constant.
On the surface of the earth on a clear day, at noon, the direct beam radiation
will be approximately 1000 watts/meter² for many locations.
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