ABSTRACT
All life on earth is ultimately dependent on the sun as a source of energy so what - ever we say about its damaging effects it must be borne in mind that we can’t do without it! This flaming incandescent mass some 93 million miles away emits a continuous spectrum of electromagnetic energy which ‘bathes’ all in its path. Near our planet the solar radiation has to penetrate the atmosphere before it reaches the earth’s surface and the skin of individ - uals who tread its surface. During its journey through the atmosphere segments of the spectrum are absorbed and attenu - ated dependent on the wavelength and energy of the radiation. The visible light part of the spectrum has very little effect on the biology of the skin. It is the ultraviolet (UV) segments that have the most relevance to us, although the infrared wavelengths at the other end can also
affect the skin. The UV radiation (UVR) has wavelengths that span 200-400 nm approximately. It is conventionally divided into short-wave UVR of 200-290 nm (UVC), medium-wave UVR of 290-320 nm (UVB) and long-wave UVR of 320-400 nm (UVA) (Figure 7.1). The atmosphere and in par - ticular the ozone layer (which is equivalent to a layer of 1-2 mm thick) absorbs most of the UVC and a significant proportion of the UVB.
