U

The sun is the major source of ultraviolet radiation. Absorption by the

ozone layer allows only wavelengths greater than 290 nm to reach the

earth’s surface. Biological effects of UV include erythema (reddening

of the skin) and skin cancer. The UV spectrum has been subdivided

into three segments. UVA (320-400 nm), UVB (280-320 nm) and

UVC (200-280 nm). UV is increasingly active with decreasing wave

length. UVA is the least active while UVC is used for its bactericidal

properties.