Editing Radiation (section)

== Non-ionizing radiation ==
{{Main|Non-ionizing radiation|Electromagnetic radiation}}
[[File:Electromagnetic-Spectrum.png|thumb|The [[electromagnetic spectrum]]]]

The kinetic energy of particles of non-ionizing radiation is too small to produce charged ions when passing through matter. For non-ionizing electromagnetic radiation (see types below), the associated particles (photons) have only sufficient energy to change the rotational, vibrational or electronic valence configurations of molecules and atoms. The effect of non-ionizing forms of radiation on living tissue has only recently been studied. Nevertheless, different biological effects are observed for different types of non-ionizing radiation.<ref name="ICNIR2003"/><ref name="Moulder">{{cite web|url=http://www.mcw.edu/gcrc/cop/static-fields-cancer-faq/toc.html |title=Static Electric and Magnetic Fields and Human Health |author=Moulder, John E. |url-status=dead |archive-url=https://web.archive.org/web/20070714054650/http://www.mcw.edu/gcrc/cop/static-fields-cancer-faq/toc.html |archive-date=14 July 2007 }}</ref>

Even "non-ionizing" radiation is capable of causing thermal-ionization if it deposits enough heat to raise temperatures to ionization energies. These reactions occur at far higher total energies than with ionization radiation, which requires only single particles to cause ionization. A familiar example of thermal ionization is the flame-ionization of a common fire, and the [[browning (food process)|browning]] reactions in common food items induced by infrared radiation, during broiling-type cooking.

The [[electromagnetic spectrum]] is the range of all possible electromagnetic radiation frequencies.<ref name="ICNIR2003"/> The electromagnetic spectrum (usually just spectrum) of an object is the characteristic distribution of electromagnetic radiation emitted by, or absorbed by, that particular object.

The non-ionizing portion of electromagnetic radiation consists of electromagnetic waves that (as individual quanta or particles, see [[photon]]) are not energetic enough to detach electrons from atoms or molecules and hence cause their ionization. These include radio waves, microwaves, infrared, and (sometimes) visible light. The lower frequencies of ultraviolet light may cause chemical changes and molecular damage similar to ionization, but is technically not ionizing. The highest frequencies of ultraviolet light, as well as all X-rays and gamma-rays are ionizing.

The occurrence of ionization depends on the energy of the individual particles or waves, and not on their number. An intense flood of particles or waves will not cause ionization if these particles or waves do not carry enough energy to be ionizing, unless they raise the temperature of a body to a point high enough to ionize small fractions of atoms or molecules by the process of thermal-ionization (this, however, requires relatively extreme radiation intensities).

=== Ultraviolet light ===
{{Main|Ultraviolet}}
As noted above, the lower part of the spectrum of ultraviolet, called soft UV, from 3&nbsp;eV to about 10&nbsp;eV, is non-ionizing. However, the effects of non-ionizing ultraviolet on chemistry and the damage to biological systems exposed to it (including oxidation, mutation, and cancer) are such that even this part of ultraviolet is often compared with ionizing radiation.

=== Visible light ===
{{Main|Light}}

Light, or visible light, is a very narrow range of electromagnetic radiation of a wavelength that is visible to the human eye, or 380–750&nbsp;nm which equates to a frequency range of 790 to 400&nbsp;THz respectively.<ref name="ICNIR2003"/> More broadly, physicists use the term "light" to mean electromagnetic radiation of all wavelengths, whether visible or not.

=== Infrared ===
{{Main|Infrared}}
Infrared (IR) light is electromagnetic radiation with a wavelength between 0.7 and 300&nbsp;μm, which corresponds to a frequency range between 430 and 1&nbsp;THz respectively. IR wavelengths are longer than that of visible light, but shorter than that of microwaves. Infrared may be detected at a distance from the radiating objects by "feel". [[Infrared sensing in snakes|Infrared sensing snakes]] can detect and focus infrared by use of a pinhole lens in their heads, called "pits". Bright sunlight provides an irradiance of just over 1&nbsp;kW/m<sup>2</sup> at sea level. Of this energy, 53% is infrared radiation, 44% is visible light, and 3% is ultraviolet radiation.<ref name="ICNIR2003" />

=== Microwave ===
{{Main|Microwave}}
[[Image:FarNearFields-USP-4998112-1.svg|thumb|upright=1.5|In electromagnetic radiation (such as microwaves from an antenna, shown here) the term "radiation" applies only to the parts of the [[electromagnetic field]] that radiate into infinite space and decrease in intensity by an [[inverse-square law]] of power so that the total radiation energy that crosses through an imaginary spherical surface is the same, no matter how far away from the antenna the spherical surface is drawn. [[Electromagnetic radiation]] includes the [[near and far field|far field]] part of the electromagnetic field around a transmitter. A part of the "near-field" close to the transmitter, is part of the changing electromagnetic field, but does not count as electromagnetic radiation.]]
Microwaves are electromagnetic waves with wavelengths ranging from as short as 1&nbsp;mm to as long as 1&nbsp;m, which equates to a frequency range of 300&nbsp;MHz to 300&nbsp;GHz. This broad definition includes both UHF and EHF (millimetre waves), but various sources use different other limits.<ref name="ICNIR2003" /> In all cases, microwaves include the entire super high frequency band (3 to 30&nbsp;GHz, or 10 to 1&nbsp;cm) at minimum, with RF engineering often putting the lower boundary at 1&nbsp;GHz (30&nbsp;cm), and the upper around 100&nbsp;GHz (3&nbsp;mm).

=== Radio waves ===
{{Main|Radio waves}}
[[File:Radio waves hazard symbol.svg|thumb|Symbol for radio waves ]]
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Like all other electromagnetic waves, they travel at the speed of light. Naturally occurring radio waves are made by lightning, or by certain astronomical objects. Artificially generated radio waves are used for fixed and mobile radio communication, broadcasting, radar and other navigation systems, satellite communication, computer networks and innumerable other applications. In addition, almost any wire carrying alternating current will radiate some of the energy away as radio waves; these are mostly termed interference. Different frequencies of radio waves have different propagation characteristics in the Earth's atmosphere; long waves may <!--surely even with long wavelengths, some will bend more than others-->bend at the rate of the curvature of the Earth and may cover a part of the Earth very consistently, shorter waves travel around the world by multiple reflections off the ionosphere and the Earth. Much shorter wavelengths bend or reflect very little and travel along the line of sight.

=== Very low frequency ===
Very low frequency (VLF) refers to a frequency range of 30&nbsp;Hz to 3&nbsp;kHz which corresponds to wavelengths of {{val|100,000|to|10,000|u=m}} respectively. Since there is not much bandwidth in this range of the radio spectrum, only the very simplest signals can be transmitted, such as for radio navigation. Also known as the [[myriametre]] band or myriametre wave as the wavelengths range from 100&nbsp;km to 10&nbsp;km (an obsolete metric unit equal to 10&nbsp;km).

=== Extremely low frequency ===
{{Main|Extremely low frequency}}
Extremely low frequency (ELF) is radiation frequencies from 3 to 30&nbsp;Hz (10<sup>8</sup> to 10<sup>7</sup>&nbsp;m respectively). In atmosphere science, an alternative definition is usually given, from 3&nbsp;Hz to 3&nbsp;kHz.<ref name="ICNIR2003" /> In the related magnetosphere science, the lower frequency electromagnetic oscillations (pulsations occurring below ~3&nbsp;Hz) are considered to lie in the ULF range, which is thus also defined differently from the ITU Radio Bands. A massive military ELF antenna in Michigan radiates very slow messages to otherwise unreachable receivers, such as submerged submarines.

=== Thermal radiation (heat) ===
{{Main|Thermal radiation}}

Thermal radiation is a common synonym for infrared radiation emitted by objects at temperatures often encountered on Earth. Thermal radiation refers not only to the radiation itself, but also the process by which the surface of an object radiates its [[thermal energy]] in the form of black-body radiation. Infrared or red radiation from a common household radiator or electric heater is an example of thermal radiation, as is the heat emitted by an operating incandescent light bulb. Thermal radiation is generated when energy from the movement of charged particles within atoms is converted to electromagnetic radiation.

As noted above, even low-frequency thermal radiation may cause temperature-ionization whenever it deposits sufficient thermal energy to raise temperatures to a high enough level. Common examples of this are the ionization (plasma) seen in common flames, and the molecular changes caused by the "[[browning (chemical process)|browning]]" during food-cooking, which is a chemical process that begins with a large component of ionization.

=== Black-body radiation ===
{{Main|Black-body radiation}}
''[[Black-body]] radiation'' is an idealized spectrum of radiation emitted by a body that is at a uniform temperature. The shape of the spectrum and the total amount of energy emitted by the body is a function of the absolute temperature of that body. The radiation emitted covers the entire electromagnetic spectrum and the intensity of the radiation (power/unit-area) at a given frequency is described by [[Planck's law]] of radiation. For a given temperature of a black-body there is a particular frequency at which the radiation emitted is at its maximum intensity. That maximum radiation frequency moves toward higher frequencies as the temperature of the body increases. The frequency at which the black-body radiation is at maximum is given by [[Wien's displacement law]] and is a function of the body's absolute temperature. A black-body is one that emits at any temperature the maximum possible amount of radiation at any given wavelength. A black-body will also absorb the maximum possible incident radiation at any given wavelength. A black-body with a temperature at or below room temperature would thus appear absolutely black, as it would not reflect any incident light nor would it emit enough radiation at visible wavelengths for our eyes to detect. Theoretically, a black-body emits electromagnetic radiation over the entire spectrum from very low frequency radio waves to x-rays, creating a continuum of radiation.

The color of a radiating black-body tells the temperature of its radiating surface. It is responsible for the color of [[stars]], which vary from infrared through red ({{val|2,500|u=K}}), to yellow ({{val|5,800|u=K}}), to white and to blue-white ({{val|15,000|u=K}}) as the peak radiance passes through those points in the visible spectrum. When the peak is below the visible spectrum the body is black, while when it is above the body is blue-white, since all the visible colors are represented from blue decreasing to red.