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Ultraviolet Radiation (UV)

Electromagnetic radiation of wavelengths of 10–400 nanometers.

The lower limit is conventionally 400 nm, though isn't a sharp cutoff. It has violet in the name because it has the highest frequencies of visible light.

It generally isn't visible to humans

  • Shorter than that of visible light
  • Longer than X-rays
  • ~10% of the total electromagnetic radiation output from the Sun
  • The photons of ultraviolet have greater energy than those of visible light
    • from about 3.1 to 12 electron volts
    • around the minimum energy required to ionize atoms

Wavelength Differences

  • longer wavelength radiation
    • excite vibrational or rotational states of these molecules
    • increasing their temperature.
  • Short-wave ultraviolet light
    • ionizing radiation
    • Consequently, short-wave UV damages DNA
    • sterilizes surfaces with which it comes into contact
    • "extreme" UV below 121 nm - ionizes air so is absorbed before it reaches the ground

Eyes

  • lens of the human eye blocks most radiation in the wavelength range of 300–400 nm
  • shorter wavelengths are blocked by the cornea

Skin Cancer

Suntan and sunburn are familiar effects of exposure of the skin to UV,

  • increased risk of skin cancer.

Types of UV

Name Wavelength (nm)
 Photon Energy Photon Energy Notes/alternative names
Ultraviolet A (UVA) 315–400 3.10–3.94
0.497–0.631 Long-wave UV, blacklight, not absorbed by the ozone-layer: soft UV.
Ultraviolet B (UVB) 280–315

 3.94–4.43
0.631–0.710 Medium-wave UV, mostly absorbed by the ozone layer: intermediate UV; Dorno radiation.
Ultraviolet C (UVC) 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 (NUV) 300–400

 3.10–4.13
0.497–0.662 Visible to birds, insects, and fish.
Middle ultraviolet (MUV) 200–300

 4.13–6.20
0.662–0.993
Far ultraviolet (FUV) 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.
Extreme Ultraviolet (EUV) 10–121

 10.25–124
1.642–19.867 Entirely ionizing radation by some definitions; completely absorbed by the atmosphere.
Far UVC 200–235

 5.28–6.20
0.846–0.993 Germicidal but strongly absorbed by outer skin layers, so does not reach living tissue.
Vacuum ultraviolet 10-200

 6.20–124
0.993–19.867 Strongly absorbed by atmospheric oxygen, though 150–200 nm wavelengths can propagate through nitrogen.

UVB

Responsible for the formation of vitamin D

Citations

  • https://en.wikipedia.org/wiki/UV-B_lamps
  • https://en.wikipedia.org/wiki/Ultraviolet
  • https://en.wikipedia.org/wiki/Light_therapy