Solar Data

Solar Energy is the amount of accumulated solar radiation energy over a period of time is measured in Langleys. 1 Langley= 11.622 Watt-hours per square meter, or 3.687 BTUs per square foot, or 41.84 kilojoules per square meter

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 per square meter (W/m2). This value is the average solar radiation measured over the time interval.

Hi Solar Radiation is the peak solar radiation measured during the time interval.

Solar Ultraviolet (UV) Data

UV Index & UV Dose

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 system. The Vantage Pro or Vantage Pro2 console can help analyze the changing levels of UV radiation and can advise of situations where exposure is particularly unacceptable. Caution: The UV 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 does the Vantage Pro take into account the dangers of pro longed exposure to UV radiation. The readings do not suggest that any amount of exposure is safe or healthful. Do not use the Vantage Pro 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. The console displays UV readings in two scales: UV Index and UV MEDs.

UV Index

The UV Index measures the intensity of UV. It was first defined by Environment Canada and since has been adopted by the World Meteorological Organization. UV Index uses a scale of 0 to 16 to rate the current intensity of UV. The UV value logged by WeatherLink is the average UV measured during the archive interval. The US EPA categorizes the UV Index values as shown below in Table 1.

Table 1 – UV Index and Exposure Category

Index Values & Exposure Category

• 0-2 Minimal
• 3-4 Low
• 5-6 Moderate
• 7-9 High
• 10+ Very High

Hi UV Index

This is the peak UV measured during the archive interval.

UV 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 Canada have developed skin type categories correlating characteristics of skin with rates of sunburn. Tables 2 and 3 below list these skin types.

Table 2 – EPA Skin Phototypes

Skin Photo type, 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
• 4 – Always tans; rarely burns Brown, dark brown, or black Rarely burns; shows very rapid tanning response

Table 3 – Environment Canada Skin Types and Reaction to the Sun Skin Type

Skin Color History of Tanning & Sun burning

• I. White - Always burns easily, never tans.
• II. White - Always burns easily, tans minimally.
• III. Light Brown - Burns moderately, tans gradually
• IV. Moderate Brown - Burns minimally, tans well.
• V. Dark Brown - Burns rarely, tans profusely.
• VI. Black - Rarely burns; shows very rapid tanning response.

UV Dose and Sunburn

Use this plot to estimate the MED dose leading to sunburn. A person with Type II (Environment Canada) skin type might choose 0.75 MED as the maximum for the day; in contrast, a person with Type V (Environment Canada) skin type might consider 2.5 MEDs a reasonable dose for the day. Note: The Vantage Pro/Vantage Pro2 consoles assume a Fitzpatrick (Environment Canada) Skin Type II. WeatherLink uses the skin factor selected in the Set Skin Type Scale Factor command in the Setup menu.