What is UV Radiation?
All radiation is a form of energy, most of which is invisible to the human eye. UV radiation is only one form of radiation and it is measured on a scientific scale called the electromagnetic (EM) spectrum1.
UV radiation is only one type of EM energy you may be familiar with. Radio waves that transmit sound from a radio station’s tower to your stereo, or between cell phones; microwaves, like those that heat your food in a microwave oven; visible light that is emitted from the lights in your home; and X-rays like those used in hospital X-ray machines to capture images of the bones inside your body, are all forms of EM energy.
UV radiation is the portion of the EM spectrum between X-rays and visible light.
More Information on UV Radiation2
Electromagnetic radiation is all around us, though we can only see some of it. All EM radiation (also called EM energy) is made up of minute packets of energy or 'particles,' called photons, which travel in a wave-like pattern and move at the speed of light. The EM spectrum is divided into categories defined by a range of numbers. These ranges describe the activity level, or how energetic the photons are, and the size of the wavelength in each category.
For example, at the bottom of the spectrum radio waves have photons with low energies, so their wavelengths are long with peaks that are far apart. The photons of microwaves have higher energies, followed by infrared waves, UV rays, and X-rays. At the top of the spectrum, gamma rays have photons with very high energies and short wavelengths with peaks that are close together.
More Information on the Electromagnetic Spectrum3
Even more Information on the Electromagnetic Spectrum4
What are the different types of UV radiation?
The most common form of UV radiation is sunlight, which produces three main types of UV rays:
UVA rays have the longest wavelengths, followed by UVB, and UVC rays which have the shortest wavelengths. While UVA and UVB rays are transmitted through the atmosphere, all UVC and some UVB rays are absorbed by the Earth’s ozone layer. So, most of the UV rays you come in contact with are UVA with a small amount of UVB.
Like all forms of light on the EM spectrum, UV radiation is classified by wavelength. Wavelength describes the distance between the peaks in a series of waves.
More Information on the Types of UV Radiation5
Both UVA and UVB rays can cause damage to your skin. Sunburn is a sign of short-term overexposure, while premature aging and skin cancer are side effects of prolonged UV exposure.
Certain oral and topical medicines, such as antibiotics, birth control pills, and benzoyl peroxide products, as well as some cosmetics, may increase skin and eye sensitivity to UV in all skin types. Check the label and ask your doctor for more information.
Sunlight is not the only source of UV radiation you may encounter. Other sources include:
More information on the Risks of Tanning6
More Information on the Known Health Effects of UV7
More Information on Health Effects of Overexposure to the Sun8
According to the World Health Organization9, brief exposure to UV radiation, about 5-15 minutes twice a week, is beneficial in helping the body produce vitamin D. However, the amount of exposure needed depends on several factors, including where you live, the time of day, and the time of year.
UV radiation, in the form of lasers, lamps, or a combination of these devices and topical medications that increase UV sensitivity, are sometimes used to treat patients with certain diseases who have not responded to other methods of therapy. Also known as phototherapy, this method of UV exposure is performed by a trained healthcare professional under the supervision of a dermatologist. Studies suggest that phototherapy can help treat unresponsive and severe cases of several diseases, including:
Phototherapy involves exposing a patient to a carefully monitored dose of UV radiation on a regular schedule. In some cases, effective therapy requires that a patient’s skin is first treated with a prescription drug, ointment, or bath that increases its UV sensitivity. While this type of therapy does not eliminate the negative side-effects of UV exposure, treatment is carefully supervised by a doctor to ensure that the benefits outweigh the risks.
More Information on the Benefits of UV Radiation15
Many factors determine how much UV you are exposed to, including:
UV rays are strongest in areas close to the equator. Because the sun is directly over the equator, UV rays only travel a short distance through the atmosphere to reach these areas. UV radiation is also the strongest near the equator because ozone16 in these areas is naturally thinner, so there is less to absorb the UV radiation.
UV exposure is lower in areas further from the equator because the sun is farther away. Exposure is also decreased because UV rays must travel a greater distance through ozone-rich portions of the atmosphere to reach the earth’s surface.
UV exposure is also greater in areas of snow, sand, pavement, and water due to the reflective properties of these surfaces.
Altitude is another contributing factor to the amount of UV. Higher altitudes have greater UV exposure because there is less atmosphere to absorb UV rays.
Time of Year
The sun’s angle in relation to the Earth varies according to season. During the summer months the sun is in a more direct angle, resulting in a greater amount of UV radiation.
Time of Day
UV is most intense at noon when the sun is at its highest point in the sky, and UV rays have the least distance to travel through the atmosphere. Especially in the hot summer months, it is a good idea to remain indoors during the peak sun hours of 10am and 4pm.
Many people believe that you cannot get sunburned on a cloudy day; this is simply not the case. Even under cloud cover it is possible to damage your skin and eyes, and cause long-term damage. It is important that you protect yourself with sunscreen, even in cloudy weather.
Some surfaces, such as snow, sand, grass, or water can reflect much of the UV radiation that reaches them. Sunglasses rated for 100% UV protection, a wide-brim hat, and broad-spectrum sunscreen can help protect your eyes and skin from reflected UV rays.
More Information on Environmental Factors of UV Exposure17
The Ultraviolet Index (UVI) is a rating scale, with numbers from 1 to 11, which indicate the amount of skin-damaging UV rays reaching the Earth’s surface during the day.
The daily UVI forecasts the amount of UV reaching your area at noon when the sun typically reaches its highest point in the sky. The higher the UVI number, the more intense the UV rays you will be exposed to.
The Environmental Protection Agency (EPA) offers UVI forecasts by ZIP code on their UV Index page18.
Many illustrations of the UVI use a system of colors to designate levels of UV exposure for a particular area on the map. The World Health Organization (WHO) has developed an internationally recognized system of colors corresponding to levels of the UVI.