What is Ultraviolet Radiation?
UV Radiation is defined as "that portion of the electromagnetic spectrum between x rays and visible light." (Health Physics Society, 2009). UV Radiation, like all other electromagnetic radiation, is composed of energy particles called photons. The below image of the EM spectrum demonstrates the size and frequency of each energy.
As you can see, Ultraviolet rays are small in length (measured in nanometers) in comparison to radio and infrared rays, and also have a relatively high frequency with only x-rays and gamma rays producing more energy. (FDA, 2007).
Ultraviolet Radiation can be broken down into three bands, based on their unique characteristics: UVA, UVB, and UVC. UVA have the longest wavelengths of the three, and UVC have the shortest. Stratospheric ozone absorbs UV radiation, but at different levels. UVC is completely absorbed, whereas only some of UVB is absorbed. UVA is not absorbed in this process.
(Courtesy of Google images)
Therefore UV radiation and its effects on the human body are related to UVA and UVB rays. UV levels themselves depend on numerous factors. The time of day, time of year, latitude, altitude, weather conditions, and reflective surfaces all affect the level of UV radiation on the earth's surface. (EPA, 1999).