W
E A T H E R
D
A T A
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E A S U R E D
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A L C U L A T E D
Solar Radiation
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S o l a r R a d i a t i o n
Note: Requires optional solar radiation sensor (#6450, included on Vantage Pro Plus
weather stations).
What we call “current solar radiation” is technically known as Global Solar
Radiation, a measure of the intensity of the sun’s radiation reaching a horizontal
surface. This irradiance includes both the direct component from the sun and the
reflected component from the rest of the sky. The solar radiation reading gives a
measure of the amount of solar radiation hitting the solar radiation sensor at any
given time, expressed in Watts /sq. m (W/m
2
).
Note:
The solar radiation sensor measures energy received in the spectral band between 400 and
1100 nm.
U V ( U l t r a Vi o l e t ) R a d i a t i o n
Note: Requires optional UV sensor (#6490), included on Vantage Pro Plus weather sta-
tions.
Energy from the sun reaches the earth as visible, infrared, and ultraviolet (UV)
rays. Exposure to UV rays can cause numerous health problems, such as sunburn,
skin cancer, skin aging, and cataracts, and can suppress the immune system. The
Weather Envoy can help analyze the changing levels of UV radiation and can
advise of situations where exposure is particularly unacceptable.
CAUTION: Be aware, however, that the UV sensor readings do not take into
account UV reflected off snow, sand, or water, which can significantly
increase the amount of UV to which you are exposed. Nor do the
readings take into account the dangers of prolonged exposure to UV
radiation. The readings do not suggest that any amount of exposure is
safe or healthful. Do not use the UV readings to determine the amount
of UV radiation to which you expose yourself. Scientific evidence
suggests that UV exposure should be avoided and that even low UV
doses can be harmful.
WeatherLink displays UV readings in two scales: UV, which is the amount of UV
radiation using the UV Index scale, and UV Dose, which displays an accumulated
UV in MEDs.
MED stands for Minimum Erythemal Dose, defined as the amount of sunlight
exposure necessary to induce a barely perceptible redness of the skin within 24
hours after sun exposure. In other words, exposure to 1 MED will result in a red-
dening of the skin. Because different skin types burn at different rates, 1 MED for
persons with very dark skin is different from 1 MED for persons with very light
skin.
Both the U.S. Environmental Protection Agency (EPA) and Environment Canada
have developed skin type categories correlating characteristics of skin with rates
of sunburn. Tables 3a and 3b below list these skin types.
