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Ultra-Violet (UV) Radiation

Ultra violet radiation is part of the electromagnetic spectrum.

It has a wavelength range from 10 - 400 nm, too short to be detected by most human eyes. The lower wavelength limit of human vision is conventionally taken as 400 nm, so ultraviolet rays are invisible to humans, although some people can perceive light at slightly shorter wavelengths than this. Insects, birds, and some mammals can see near-UV (i.e., slightly shorter wavelengths than what humans can see).

 

Production of UV

UV radiation is present in sunlight, making up about 10% of the total electromagnetic radiation output from the Sun. It is also produced by electric arcs and specialized lights, such as mercury-vapor lamps, tanning lamps, and black lights.

The UV spectrum has effects both beneficial and harmful to life

Long-wavelength ultraviolet is not an ionising radiation - its photons are of too low energy to ionize atoms, but it can cause chemical reactions and causes many substances to glow or fluoresce. The chemical and biological effects important, and many practical applications of UV radiation derive from its interactions with organic molecules.

Short-wave ultraviolet is ionising - it damages DNA and kills bacteria. It is therefore used to sterilise surfaces.

The UV light produced by the Sun would kill the life on Earth's dry land if most of the UV were not filtered out by the atmosphere. The more energetic, shorter-wavelength "extreme" UV below 121 nm ionises air so strongly that it is absorbed before it reaches the ground. The ozone layer plays an important part in this - mankind's damage to this was a serious problem.

For humans, suntan and sunburn are familiar effects of exposure of the skin to UV light, along with an increased risk of skin cancer. Ultraviolet light (specifically, UVB) is also responsible for the formation of vitamin D in most land vertebrates, including humans.

Name
Abbreviation
Photon energy
(eV, aJ)
Notes/alternative names
Ultraviolet A
UV-A
315–400
3.10–3.94,
0.497–0.631
Long-wave UV, black light, not absorbed by the ozone layer: soft UV.
Ultraviolet B
UV-B
280–315
3.94–4.43,
0.631–0.710
Medium-wave UV, mostly absorbed by the ozone layer: intermediate UV; Dorno [de] radiation.
Ultraviolet C
UV-C
100–280
4.43–12.4,
0.710–1.987
Short-wave UV, germicidal UV, ionizing radiation at shorter wavelengths, completely absorbed by the ozone layer and atmosphere: hard UV.
Near ultraviolet
N-UV
300–400
3.10–4.13,
0.497–0.662
Visible to birds, insects, and fish.
Middle ultraviolet
M-UV
200–300
4.13–6.20,
0.662–0.993
Far ultraviolet
F‑UV
122–200
6.20–10.16,
0.993–1.628
Ionizing radiation at shorter wavelengths.
Hydrogen
Lyman-alpha
H Lyman-α
121–122
10.16–10.25,
1.628–1.642
Spectral line at 121.6 nm, 10.20 eV.
E-UV
10–121
10.25–124,
1.642–19.867
Entirely ionizing radiation by some definitions; completely absorbed by the atmosphere.
Vacuum ultraviolet
V-UV
10–200
6.20–124,
0.993–19.867
Strongly absorbed by atmospheric oxygen, though 150–200 nm wavelengths can propagate through nitrogen.

'aJ' is 'atto joules' - atto is an S.I. Prefix for (x 10-18) so 1 aJ = 1 x x 10-18J

Click here to see uses of UV

See the section on the depletion of the ozone layer and skin cancers in the news section