Philippe Martin, Coordinator of the UV program at Environment Canada, says the UV index scale was developed in Canada and is now an international program used everywhere in the world.
He says UV rays become stronger as you move south in tropical regions and are much higher than in Canada, adding that it’s an open-ended scale. The UV index is 3 or higher then protect your skin by wearing clothing that covers as much skin as possible, seek shade, use sunscreen, wear sunglasses, and a wide-brimmed hat. Martin says these same measures are obviously applied even more strictly if the index continues to rise up to 6 or 7. “More particularly if you have pale, white skin that always burns and never tans.”
Martin says scientists estimate the UV Index based on three variables/conditions. The thickness of the ozone layer in the upper atmosphere, as a thick ozone absorbs more UV. The 2nd variable is the angle of the sun, which is called the solar constant. The third element is the amount of cloud cover.
The UV index is grouped into five levels of risk; (Low 0-2) (Moderate 3-5) (High 6-7) (Very High 8-10) (11 or more Extreme) (Main source: Thunder Bay District Health Unit, Pembina Valley Online News)