<physics> Continuous spectrum beyond the violet end of the visible spectrum (wavelength less than 400nm) and above the X-ray wavelengths (greater than 5 nm).

Glass absorbs UV, so optical systems at these wavelengths have to be of quartz. Nucleic acids absorb UV most strongly at around 260nm and this is the wavelength most likely to cause mutational damage (by the formation of thymine dimers).

It is the UV component of sunlight that causes actinic keratoses to form in skin, but that is also required for Vitamin D synthesis.

This entry appears with permission from the Dictionary of Cell and Molecular Biology

(11 Mar 2008)