Tuesday, June 3, 2008

UV Index Chart

What is UV Index?
The UV Index is a next day forecast of the amount of skin damaging UV radiation expected to reach the earth's surface at the time when the sun is highest in the sky (solar Noon). The amount of UV radiation reaching the surface is primarily related to the elevation of the sun in the sky, the amount of ozone in the stratosphere, and the amount of clouds present. The UV Index can range from 0 (when it is nighttime) to 15 or 16 (in the tropics at high elevations under clear skies). UV radiation is greatest when the sun is highest in the sky and rapidly decreases as the sun approaches the horizon. The higher the UV Index, the greater the dose rate of skin damaging (and eye damaging) UV radiation. Consequently, the higher the UV Index, the shorter the time before skin damage occurs.
There are two prices to pay for overexposure to UV radiation: a severe sunburn following an intense short term overexposure, and the more serious skin cancers developing after long term overexposure. Melanoma, the more deadly of the two types of skin cancer, occurs when the person has been subjected to several intense short term overexposures.
Non-melanoma skin cancers, which are almost 100% curable, occur in people who are overexposed for very long periods of time, such as construction workers, farmers, or fishermen.
Long term overexposure to UV radiation has been linked to the formation of cataracts in the eyes as well.
The UV Index is a forecast of the probable intensity of skin damaging ultraviolet radiation reaching the surface during the solar noon hour (11:30-12:30 local standard time or 12:30-13:30 local daylight time). The greater the UV Index is the greater the amount of skin damaging UV radiation. How much UV radiation is needed to actually damage one's skin is dependent on several factors. But in general the darker one's skin is, (that is the more melanin one has in his/her skin) the longer (or the more UV radiation) it takes to cause erythema (skin reddening). The EPA has devised general guidelines as far as what to do to protect oneself from overexposure to UV radiation. These are shown in the table below:
For today's UV Index, click here .
Exposure Category UV Index Protective Actions
Minimal 0, 1, 2 Apply skin protection factor (SPF) 15 sun screen
Low 3, 4 SPF 15 & protective clothing (hat)
Moderate 5, 6 SPF 15, protective clothing and UV-A&B sun glasses
High 7,8,9 SPF 15, protective clothing, UV-A&B sun glasses, and attempt to avoided the sun between 10am and 4pm
Very High 10+ SPF 15, protective clothing, UV-A&B sun glasses and attempt to avoid the sun
What does an SPF rating mean on my suntan lotion bottle?
The letters SPF stand for Sun Protection Factor, but dermatologists wish people didn't think the numbers offered a license to tan. A factor is a number used to multiply another number. In this case, your time in the sun before burning. An SPF of 2 means that if you usually start to burn in 20 minutes, using the product would, in a perfect world, let you bask in the sun twice as long before you burn, assuming that the product is fresh and full strength, that you apply enough, and that you don't swim or sweat it off.
The almost universal medical advice is to talk about sunscreen or sun block, not suntan and certainly not sunburn. And almost universally, dermatologists say that an SPF of 15 is what you routinely need to help you protect your skin just before burns. And a burn is the tip of the iceberg. The SPF estimates only the amount of protection provided against ultra-violet B rays, the so-called burning rays, which attack the skins surface while insidious damage is done by the deeply penetrating UVA rays, which destroy the skins support structure. Some products will cut down on both kinds.

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