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Ultraviolet Radiation

visible spectrum lightThe sun emits radiation in a broad spectrum called the electromagnetic spectrum, a small portion of which is visible. The visible spectrum can be seen when cloud droplets separate light in a rainbow. The visible spectrum is red, orange, yellow, green, blue, indigo and violet. Ultraviolet (UV) Radiation is outside of the visible range near violet, hence the name.

There are several levels of UV Radiation. UV-A helps plants grow and helps our bodies make Vitamin D, but also causes sunburn and cataracts. UV-B causes damage to the DNA within skin. More information on UV Radiation and its affects can be found at: http://earthobservatory.nasa.gov/Library/UVB/.

The ozone layer in the stratosphere helps to reduce the amount of UV Radiation that reaches the surface. On the ground ozone is a pollutant the causes lung damage. One thing to remember about ozone is "good up high, bad nearby". More information about ozone as a ground level pollutant can be found at: http://www.maine.gov/dep/air/ozone/ozone_health.html.

It is important to protect yourself against over exposure to the sun. Too much sun (UV rays) can lead to skin cancer, pre-mature aging of the skin, other skin problems, cataracts, other damage to the eyes, and can suppress the immune system. The prudent use of sunscreen, keeping skin covered, and seeking shady areas will greatly reduce your chances of suffering damage from UV radiation.

EPA has launched a UV Index to classify the level of risk. This index indicates the level of risk you are likely to encounter on a given day and is displayed in the chart below.

Category
Index Number

Sun Protection Messages

Low
1-2

Wear sunglasses on bright days. In winter, reflection can nearly double UV strength.

If you burn easily, cover up and use sunscreen.

Moderate
3-5

Take precautions, such as covering up and using sunscreen.

Remain in the shade near midday.

High
6-7

Protection against sunburn is needed.

Reduce time in the sun between 11AM and 4PM, cover up, wear a hat & sunglasses and use sunscreen.

Very High
8-10

Take extra precautions, sunburn will occur quickly.

Avoid the sun between 11AM and 4PM. Seek shade, cover up, wear a hat & sunglasses and use sunscreen.

Extreme
11+

Take all precautions, skin will burn in minutes!

Avoid the sun between 11AM and 4PM. Seek shade, cover up, wear a hat & sunglasses and use sunscreen.

 

The level of risk varies from place to place, season to season, and hour to hour. There are a number of factors that affect the level of risk:

  • In the northern hemisphere the sun's rays are stronger in the spring and summer;
  • Heavy cloud cover can block most UV radiation;
  • UV radiation peaks when the sun reaches its highest point in the sky so the best time to be out of the sun is from 11AM to 4PM;
  • UV radiation increases with altitude due to thinner air;
  • UV radiation is strongest near the equator and declines toward the poles due to the curvature of the earth; and
  • UV radiation can be scattered by ground surfaces (as much as 80% can be reflected by snow, sand can reflect 15%, and 10% can be reflected by water).

FORECAST UV INDEX: To help figure out the level of risk you will face tomorrow EPA has created an online calculator which can be accessed at: http://www.epa.gov/sunwise/uvindex.html. Just type in your zip code and tomorrow's UV Index is given along with a description of what you can do to protect yourself at that level. At this same web site visitors can register for free e-mail UV Alerts. EPA and the National Oceanic and Atmospheric Administration's National Weather Service (NWS) developed and launched the UV Alert System that notifies subscribers when solar UV radiation and the risk of overexposure is predicted to be unusually high.

For more information you can use your favorite search engine and type in words like: ultraviolet radiation, ozone, electromagnetic spectrum, skin cancer, etc. The links below will also provide more information.

http://www.epa.gov/sunwise/

http://www.weather.com/activities/health/skin/?from=healfl

Visible Spectrum graphic created by Kevin Ostrowski, MEDEP-BAQ