Non-ionizing radiation

Different types of electromagnetic radiation

Non-ionizing (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. 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.

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, or accelerate radical reactions, such as photochemical aging of varnishes or the breakdown of flavoring compounds in beer to produce the "lightstruck flavor". Near ultraviolet radiation, although technically non-ionizing, may still excite and cause photochemical reactions in some molecules. This happens because at ultraviolet photon energies, molecules may become electronically-excited and/or promoted to free-radical form, even without ionization taking place.

The light from the Sun that reaches the earth is largely composed of non-ionizing radiation, since the ionizing far-ultraviolet rays have filtered out by the gases in the atmosphere, particular oxygen. The remaining ultraviolet radiation from the Sun is in the non-ionizing band, and causes molecular damage by photochemical and free-radical-producing means that do not ionize.

Health risks

Non-ionizing radiation hazard sign

Non-ionizing radiation can produce non-mutagenic^{[citation needed]} effects such as inciting thermal energy in biological tissue that can lead to burns.

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).

	Source	Wavelength	Frequency	Biological effects
UVA	Black light, sunlight	318–400 nm	750–950 THz	Eye – photochemical cataract; skin – erythema, inc. pigmentation
Visible light	Lasers, sunlight, fire, LEDs, light bulbs	400–780 nm	385–750 THz	Skin photoaging; eye – photochemical & thermal retinal injury
IR-A	Lasers, remote controls	780 nm – 1.4 µm	215–385 THz	Eye – thermal retinal injury, thermal cataract; skin burn
IR-B	Lasers	1.4–3 µm	100–215 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, long-distance telecommunications, radar, Wi-Fi	1 mm – 33 cm	1–300 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	Strong magnets, MRI	Infinite	0 Hz	Magnetic – vertigo/nausea; electric – charge on body surface

Ultraviolet radiation

Ultraviolet light can cause burns to skin and cataracts to the eyes. Ultraviolet is classified into near, medium and far UV according to energy, where near and medium ultraviolet are technically non-ionizing, but where all UV wavelengths can cause photochemical reactions that to some extent mimic ionization (including DNA damage and carcinogenesis). UV radiation above 10 eV (wavelength shorter than 125 nm) is considered ionizing. However, the rest of the UV spectrum from 3.1 eV (400 nm) to 10 eV can produce photochemical reactions that are damaging to molecules by means other than simple heat.

Ultraviolet light even in the non-ionizing range can produce free radicals that induce cellular damage, and can be carcinogenic. Photochemistry such as pyrimidine dimer formation in DNA can happen through most of the UV band, including much of the band that is technically non-ionizing. Ultraviolet light 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.

See also

• Ionizing radiation
• Electromagnetic hypersensitivity
• Mobile phone radiation and health
• Electromagnetic radiation and health
• Wireless electronic devices and health
• Electronic harassment

External links

• Health Physics Society Public Education website