Ultraviolet light (UV light) is nothing but packet of energy which has a wavelength lower than the visible spectrum, but because of very high frequency has intense energy. Ultraviolet (UV) radiation forms part of the electromagnetic spectrum with wavelengths between 200 nm and 400 nm and is divided into three further components, UVA (320–400 nm), UVB (280–320 nm) and UVC (200–280 nm) (WHO-INCHEM, 1994).
The ozone layer normally absorbs UVC, but now with ozone depletion, even UVC is gaining importance particularly with respect to skin cancers.
The energy carried by each portion of the spectrum is inversely related to its wavelength. UVA has the greatest wavelength, thus the least energy. However, the depth of penetration of UV light into the skin increases with increasing wavelength.
Thus UVA has the maximum penetration, and the greatest role in aging changes. It has been harnessed for medical benefits, but can have severe adverse effects in unprotected situations. The peak of UV-induced carcinogenicity has been shown to lie within the UVB portion of the UV (Clynesdale, 2001)