Ultraviolet

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Ultraviolet is a color of light which is invisible to men, but can be recognized by many animals, mostly insects, reptiles, and small birds. The frequency of ultraviolet is higher than that of violet light, hence the name 'ultraviolet'.

The name 'ultraviolet' is in part derived from the ancient Latin language. The prefix ultra- means 'behind', 'beyond', or 'far'. Ultraviolet is beyond the visible violet light in terms of frequency, wavelength, and energy.

UV is a common abbreviation of ultraviolet, mainly used in technical environments.

Ultraviolet light can be dangerous to one's health. For instance, sunlight contains UV rays that can cause sunburn and lead to various cancers. Industrial UV rays, which often emanate from X-ray machines, can induce cancer and render people infertile.

There is no clear-cut distinction between X-rays and ultraviolet, only that the low-energy, low-frequency, large-wavelength ultraviolet in the neighborhood of visible violet is not suitable for X-raying, whereas the even-higher-energetic, even-higher-frequency, even-shorter-wavelength X-rays are a component of radioactivity which is called gamma rays, or gamma radiation.

Technically, electromagnetic waves with a frequency of 789 terahertz or more are called ultaviolet. This corresponds with a wavelength from 380 nanometers down to approximaltey 5 nanometers. A single light quantum of ultraviolet carries an energy around some 3.26 electron volt, the more, the higher its frequency.

Although the air of the earth is transparent to a broad range of ultraviolet, some ultraviolet sunlight is absorbed at a very high altitude by the ozone layer. Recent and ongoing destruction of ozone in high altitudes caused by human influence - mostly by industrial chemicals and air travel - has greatly increased the amount of ultraviolet light reaching the earth surface. This, in turn, the risk of skin cancer to mankind, and this risk will only increase with time.

Ultraviolet of wavelengths less than 200 nanometers, X-rays, and gamma rays, are collectively called ionizing radiation since the energy in any such light quantum is high enough to 'kick' an electron out of an atom. This is the reason why these kinds of radiation are dangerous to life.

Ordinary glass does not let radiation through if its wavelength is less than 200 nanometers, so it acts as a shield against the more dangerous range of ultraviolet light, but some special sorts of glass do not shield as well, including many car windows.