ABSTRACT
Ultraviolet (UV) radiation is that portion of the electromagnetic spectrum that extends from the lower wavelength limit of human vision (usually defined as 380 to 400 nm) to wavelengths as short as about 10 nm, where it overlaps the x-ray region. In the natural environment, the shortest wavelength of sunlight that can be routinely measured at the earth’s surface is about 290 nm, largely due to the absorption properties of ozone and other atmospheric gases. So, the only environmentally relevant UV region is from 290 to 380 nm. However, artificial UV sources, such as certain fluorescent lamps, mercury and xenon arcs, and lasers, are readily available and extend the possibility of exposure of biological specimens to UV down to wavelengths of about 190 nm. Below 190 nm, air (oxygen) and water begin to absorb UV heavily, making it difficult to expose biological samples except under extreme conditions (e.g., in a vacuum). Hence, the focus of UV photobiology is mainly on the effects on biological processes due to exposure to photons in the wavelength range of 190 to 380 nm.
