Sunlight and Ultraviolet Exposure

The sun is a star roughly 150 million kilometres away from the earth. Without the sun, life on Earth would not exist - our planet would be frozen and dark.

A nuclear reaction at the sun's core transforms hydrogen into helium and generates massive amounts of radiation, or energy. These forms of energy (known collectively as the electromagnetic spectrum) include radiowaves, microwaves, infrared radiation, visible light, ultraviolet radiation, X-rays, and gamma rays.

Depending on its wavelength, different types of solar radiation do different things. For instance, infrared radiation makes us feel the warmth of the sun, visible light allows us to see the world around us, and ultraviolet radiation affects our health.

Electomagnetic Radiation Spectrum

What is ultraviolet radiation?

Ultraviolet radiation (UVR) is invisible sun energy in the wavelength range from 100 to 400 nanometers (nm). It is shorter and more energetic than visible light, and depending on its wavelength, it is able to penetrate the ozone layer and trigger different biological effects.

UVR is divided into three wavelength ranges:

• UVA is long-range ultraviolet radiation between 320 and 400nm. Although not as energetic as UVB, UVA has the ability to penetrate deep into the skin, causing immediate tanning, premature skin ageing and playing a role in the development of certain skin cancers. UVA is not readily absorbed by the ozone layer - about 95% gets through.
• UVB is short-wave ultraviolet radiation between 280 and 320nm. It can penetrate the epidermis and is responsible for delayed tanning, sunburns and most skin cancers. A large portion of UVB is absorbed by the ozone layer - only 5% reaches the planet's surface.
• UVC, with wavelengths between 100 and 280nm, is very energetic, and therefore very dangerous to all forms of life (even with short exposures). However, UVC radiation is filtered out by the ozone layer, and therefore never reaches the earth.

Ultraviolet radiation can also be generated by artificial sources, including tanning equipment and lasers. But remember: UVR can be dangerous, no matter where it comes from.

For more information, consult Health Canada's Ultraviolet Radiation webpage or  Environment Canada's Stratospheric Ozone website.