Ultraviolet Light (UV)

A segment of the electromagnetic spectrum in the range of wavelengths 10-400 nanometers (nm).  The frequencies of UV light are not visible to the human eye, and exposure to this radiation requires protective measures.  The effect of UV light on public health usually refers to the 100-400nm wavelength range, which is divided into 3 sub-segments:

UVA (315-400nm)

UVB (280-315nm)

UVC (100-280nm)

Ultraviolet radiation emanating from the sun and reaching the earth is mainly of the UVA type (95%), with a small amount of UVB (5%).  The remaining range is completely absorbed by the atmosphere, mainly by oxygen.  This radiation is also emitted by artificial sources, such as halogen or fluorescent bulbs.