UV RADIATION & YOU

The sun gives off many different types of radiation. As well as visible light or sunlight, there is invisible radiation. One type of invisible radiation is infra-red radiation, which generates heat. The other variety is ultraviolet (UV) radiation. UV radiation is not warm—we can neither see nor feel it—but it causes both sunburn and skin cancer. It also causes the skin to age prematurely and to become leathery, roughened and blotchy. Exposure to UV radiation over long periods can also damage the eyes. It can cause cataracts which, if untreated, leads to blindness.

The A B C of UV Radiation

UV radiation is made up of three components: UV-A, UV-B and UV-C. The harmful effects of UV-B and UV-C have been known for some time (no UV-C from the sun reaches the earth’s surface; it is all absorbed by the ozone layer). UV-A was, until recently, thought to be relatively harmless, but evidence is emerging that UV-A not only contributes to skin damage but also increases the risk of developing skin cancer. Remember, UV radiation is present in the sun’s rays throughout the year in varying amounts.

Factors affecting UV radiation levels

Factors that affect UV radiation include the following:

• Sun elevation: The higher the sun in the sky, the more intense the UV radiation. Therefore the UV radiation levels are highest around solar noon and in summer

• Time of the year: In Canada, UV radiation levels are usually many times higher in summer than in winter. In SW Ontario, for example, sunburn can occur in as little as 15 minutes on a fine July day. The highest risk months are usually from May through to September.

• Time of the day: The danger period for UV radiation is from 11am to 4pm. At least 60% of the day’s UV radiation is between these times; these are the hours when you’ll burn fastest.

• Latitude: The closer to equatorial regions, the higher the UV radiation levels.

• Cloud cover: Solar UV radiation can penetrate through light cloud cover, and on lightly overcast days the UV radiation intensity can be similar to that of a cloud-free day. Heavy cloud can reduce the intensity of UV radiation.  Random clouds have a variable effect on UV radiation levels, which rise and fall as clouds pass in front of the sun.

• Temperature: Temperature does not affect UV radiation levels. Temperature is due to the sun’s infra-red rays heating up the Earth and is not related to the amount of UV radiation present. Maximum daily temperatures are usually in the late afternoon; UV radiation, however, peaks when the sun is overhead—about midday (1pm during daylight saving time). Typically, more people get sunburnt when the temperature is between 18-27 degrees than when it is in the 30’s, usually because they don’t think about sun protection during the cooler temperatures.

• Altitude: The risks are much greater high up on a mountain slope than at sea level, because the thinner atmosphere at high altitude filters out much less of the UV radiation. At an altitude of around 2,000 metres the amount of UV radiation can be as much as 30% higher than at sea level.

• Ozone: Ozone absorbs some of the UV radiation (UV-C) that would otherwise reach the Earth's surface. It’s important to note that the decrease in ozone levels and the seasonal ‘hole’ in the Ozone layer haven’t yet been linked to high rates of skin cancer.

• Ground reflection: Grass, soil and water reflect less than 10% of UV radiation; fresh snow reflects as much as 80%; dry beach sand about 15% and sea foam about 25%.

Scattered UV radiation

Some UV radiation reaches you directly from the sun; but much of it is scattered about the sky and reaches you indirectly. In general you receive as much scattered UV radiation from the sky as you receive directly from the sun.

You’ll get more UV radiation if you’re out in the open, where there are few buildings or other objects to block out parts of the sky—on the beach or boating, for example. Here you’re exposed to scattered UV radiation from the whole sky, as well as to the UV radiation reflected from sand or water. And because of the scattered and reflected UV radiation, a beach umbrella (for example) can only offer partial protection and therefore you still need clothing and sunscreen.             

UV radiation from other sources

Tanning salons advertise ‘safe tanning’ encouraging you to tan indoors and avoid sunburn and skin cancer. However, recent research suggests that UV radiation from tanning lights is a contributing cause of skin cancer. The Canadian Cancer Society and the Canadian Dermatology Association as well as Health Canada strongly recommend that people do not add to their UV radiation exposure by using tanning lights.

If your occupation involves you being exposed to UV radiation either from the sun or from artificial sources, you might talk to your Occupational Health and Safety Officer about safety measures. The Grey Bruce Health Unit has literature directly related to workplace UV radiation exposure.

Possible sources of artificial UV radiation include: electric and plasma arc welding and cutting tools; gas or vapour pressure discharge lamps used in lighting, curing paint, inks and other materials; bacterial and fungicidal cabinets and lamps; molten metal presses (only those that operate at 2500°K or more). Fluorescent lights and halogen lamps also emit UV radiation, but research suggests that they do not pose a risk, particularly if they are fitted with diffusers.