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How Much UV Reaches Me?


Wednesday, July 31, 2013, 1:54 PM - You get more UV, and sunburn faster, when the sun's rays are stronger.

The amount of UV you receive depends on these factors:

• The time of day. UV is greatest at midday (when the sun is highest in the sky), and less in early morning or late afternoon.
• The season. UV is greatest in the spring and summer (April to August), less in fall, and least in the winter.
• How long you're out in the sun. The longer you are out in the sun, the more UV you receive.
• Cloud Cover. A thick, heavy layer of cloud blocks UV. However, puffy, fair-weather clouds or layers of thin, light cloud let most of it through. So, the darker the clouds, the less the UV. Be careful under thin clouds - the sun's rays may not feel hot, but they can still burn. And watch out for haze, because it does not block UV.
• The type of surface you are on. You get much more UV on snow, sand or concrete, since these surfaces reflect the sun's rays back onto your skin, just like a mirror. The brighter the surface, the more UV is reflected - fresh snow and dry sand reflect the most.
• Your elevation. You get more UV on a mountain than at lower elevations, as the air is clearer and thinner.
• Where you are on the earth's surface. UV is strongest at the equator, and gets weaker as you go towards the poles. The poles receive the least UV. If you live in southern Canada, you will receive more UV than if you live in the Arctic.
• What you're wearing. Summer clothes generally expose more skin to UV.

The sun delivers the most UV when it is high overhead at midday in the spring or summer. A good rule of thumb is: "if your shadow is shorter than you are, you must protect yourself from the sun.

Don't confuse temperature and UV. Light cloud or a breeze can make you feel cooler - but they don't reduce the UV. UV rays can burn even if it's cold!

Information Courtesy of Environment Canada

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