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Different types of electromagnetic radiation

Non-ionizing radiation or non-ionising radiation refers to any type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules — that is, to completely remove an electron from an atom or molecule.[1] Instead of producing charged ions when passing through matter, the electromagnetic radiation has sufficient energy only for excitation, the movement of an electron to a higher energy state. Nevertheless, different biological effects are observed for different types of non-ionizing radiation.[2][3]

Near ultraviolet, visible light, infrared, microwave, radio waves, and low-frequency RF (longwave) are all examples of non-ionizing radiation. Visible and near ultraviolet may induce photochemical reactions, ionize some molecules or accelerate radical reactions, such as photochemical aging of varnishes[4] or the breakdown of flavoring compounds in beer to produce the "lightstruck flavor".[5] The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, with the notable exception of some ultraviolet rays. However, most ionizing radiation is filtered out by the atmosphere (see Earth's atmosphere). Static fields do not radiate.[3]

Health risks

Non-ionizing radiation hazard sign

Non-ionizing radiation is less mutagenic than ionizing radiation. Non-ionizing radiation mostly causes the formation of pyrimidine dimers, while ionizing radiation can cause altered DNA bases, single strand breaks, and double strand breaks (see DNA repair). The pyrimidine dimers are much easier to repair and, thus, pose much lower health risk. Non-ionizing radiation can still be absorbed by the tissue and will produce a heating effect.

In terms of potential biological effects, the non-ionizing portion of the spectrum can be subdivided into:

  1. The optical radiation portion, where electron excitation can occur (visible light, infrared light)
  2. The portion where the wavelength is smaller than the body, and heating via induced currents can occur (MW and higher-frequency RF)
  3. The portion where the wavelength is much larger than the body, and heating via induced currents seldom occurs (lower-frequency RF, power frequencies, static fields)[3]
[2] Source Wavelength Frequency Biological effects
UVA Black light, sunlight 318 nm - 400 nm 750 THz - 950 THz Eye – photochemical cataract; skin – erythema, inc. pigmentation
Visible light Lasers, sunlight, fire, LEDs, light bulbs 400 nm - 780 nm 385 THz - 750 THz Skin photoaging; eye – photochemical & thermal retinal injury
IR-A Lasers, remote controls 780 nm - 1.4 µm 215 THz - 385 THz Eye – thermal retinal injury, thermal cataract; skin burn
IR-B Lasers, long-distance telecommunications 1.4 µm - 3 µm 100 THz - 215 THz Eye – corneal burn, cataract; skin burn
IR-C Far-infrared laser 3 µm - 1 mm 300 GHz - 100 THz Eye – corneal burn, cataract; heating of body surface
Microwave PCS phones, some mobile/cell phones, microwave ovens, cordless phones, motion detectors, radar, Wi-Fi 1 mm - 33 cm 1 GHz - 300 GHz Heating of body tissue
Radio-frequency radiation Mobile/cell phones, television, FM, AM, shortwave, CB, cordless phones 33 cm - 3 km 100 kHz - 1 GHz Heating of body tissue, raised body temperature
Low-frequency RF Power lines > 3 km < 100 kHz Cumulation of charge on body surface; disturbance of nerve & muscle responses
Static field[3] Strong magnets, MRI Infinite 0 Hz Magnetic – vertigo/nausea; electric – charge on body surface
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Ultraviolet radiation

Ultraviolet light can cause burns to skin[6] and cataracts to the eyes.[6] Ultraviolet is classified into near, medium and far UV according to energy, where near ultraviolet is non-ionizing. Ultraviolet light produces free radicals that induce cellular damage, which can be carcinogenic. Ultraviolet light also induces melanin production from melanocyte cells to cause sun tanning of skin. Vitamin D is produced on the skin by a radical reaction initiated by UV radiation.

Plastic (polycarbonate) sunglasses generally absorb UV radiation. UV overexposure to the eyes causes snow blindness, which is a risk particularly on the sea or when there is snow on the ground.

Visible and infrared, lasers

Visible light causes few effects to the human body. Bright visible light irritates the eyes. Visible-light lasers have much more powerful effects and may damage the eyes even at small powers. Very strong visible light is used for cauterizing hair follicles.

Visible light can also ionize DNA.[7]

Microwave and radio-frequency radiation

  • Biological effects
    • Effects on the skin
    • Effects on the eyes
    • Other hazards
  • Occupational exposure standards

Low-frequency ELF

  • Biological effects
    • Effects on the skin
    • Effects on the eyes
    • Other hazards
  • Occupational exposure standards

Static fields

  • Biological effects
  • Occupational exposure standards

See also

External links

References

  1. ^ "Ionizing & Non-Ionizing Radiation". http://www.epa.gov/radiation/understand/ionize_nonionize.html.  
  2. ^ a b Kwan-Hoong Ng (20th – 22nd October 2003). [http://www.who.int/peh-emf/meetings/archive/en/keynote3ng.pdf "Non-Ionizing Radiations – Sources, Biological Effects, Emissions and Exposures"] (PDF). Proceedings of the International Conference on Non-Ionizing Radiation at UNITEN ICNIR2003 Electromagnetic Fields and Our Health. http://www.who.int/peh-emf/meetings/archive/en/keynote3ng.pdf.  
  3. ^ a b c d John E. Moulder. "Static Electric and Magnetic Fields and Human Health". http://www.mcw.edu/gcrc/cop/static-fields-cancer-FAQ/toc.html.  
  4. ^ Helv. Chim. Acta vol. 83 (2000), pp. 1766. [1]
  5. ^ Photochem. Photobiol. Sci., 2004, 3, 337 - 340, DOI: 10.1039/b316210a [2]
  6. ^ a b "UW EH&S Hazards of Ultraviolet Light". http://www.ehs.washington.edu/rsononion/uvlight.shtm.  
  7. ^ [3]

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