Ultraviolet Radiation
UVR cannot be seen or felt – it’s not related to visible light or to temperature.
What is UVR?
How does it reach me?
what’s the UV Index?
Ultraviolet Radiation
What is UVR?
Ultraviolet Radiation, or UVR, is electromagnetic radiation emitted by the sun and artificial sources, like tanning beds.
UVR cannot be seen or felt – it’s not related to visible light or to temperature.
The UV spectrum can be subdivided into three types: UVA, UVB, and UVC.
Only UVA and UVB radiation reach the earth’s surface. UVB radiation is generally associated with sunburns though both types of UVR can cause skin damage, skin aging and skin cancer.
How does it reach me?
Direct and Indirect Sources of UVR
Directly, from the sun
Maximum UVR levels occur when the sun is at its highest point in the sky (solar noon) during the summer months. Most of the daily total UVR is received within 2 hours before and after of solar noon. This is why most sun safety communications encourage people to take extra precautions or to avoid outdoor activities between 11:00 am and 3:00 pm (the Critical Protection Period) from April to September.
Indirectly, scattered by clouds or other particles in the atmosphere
UVR levels are highest under cloudless skies, but UVR levels can remain high especially during thin or scattered cloud cover. Some clouds can actually increase the UVR intensity on the ground by reflecting the sun’s rays back towards earth.
Indirectly, reflected from surfaces
UVR is reflected or scattered to varying extents by different surfaces. For example, snow can reflect as much as 80 % of UVR, dry beach sand about 15%, and sea foam about 25%.
Think UV when you check the weather
What is the UV Index?
The UV Index is a rating system adopted from the World Health Organization, as a way of describing the amount of UVR at the earth’s surface.
- The higher the number, the stronger the UV levels and the less time it takes for the sun to damage the skin.
- The UV index can help to determine the level of precaution you should take before heading outside.
- Sun protection measures should be taken anytime the UV index is 3 or higher.
- UV Index can reach up to 10 in Canada and higher in other parts of the world.
- Ensure to check the daily forecast for the UV Index and protect your skin accordingly.
View sources
The Surgeon General’s Call to Action to Prevent Skin Cancer. Washington, DC: U.S. Dept of Health and Human Services, Office of the Surgeon General; 2014. View
The Recommended Core Content for Sun Safety Messages in Canada. Briefing on the Results of the 2014/15 National Consensus Process.
Figure adapted with permission from Guidelines to Shade, Cancer Council NSW, Sydney, 2013.