Weather Data Measured & Calculated
21
UV (Ultra Violet) Radiation
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 sun-
burn, skin cancer, skin aging, and cataracts, and can suppress the immune sys-
tem. 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 accu-
mulated 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
reddening 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 Can-
ada have developed skin type categories correlating characteristics of skin
with rates of sunburn. Tables 3a and 3b below list these skin types.
Table A1: EPA Skin Phototypes
Skin Phototype Skin color Tanning & Sunburn history
1 - Never tans,
always burns
Pale or milky white;
alabaster
Develops red sunburn; painful swelling,
skin peels
2 - Sometimes
tans, usually burns
Very light brown;
sometimes freckles
Usually burns, pinkish or red coloring
appears;
can gradually develop light brown tan
3 - Usually tans,
sometimes burns
Light tan; brown, or
olive;
distinctly pigmented
Rarely burns; shows moderately rapid
tanning response
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