Infrared

Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than visible light, but shorter than microwave radiation. The name means "below red" (from the Latin infra, "below"), red being the color of visible light of longest wavelength. Infrared radiation spans three orders of magnitude and has wavelengths between 700 nm and 1 mm.

Applications

Night Vision

Infrared is used in night-vision equipment, when there is insufficient visible light to see an object. The radiation is detected and turned into an image on a screen, hotter objects showing up brighter, enabling the police and military to acquire thermally significant targets, such as human beings and automobiles. Also see Forward looking infrared.

Related Topics:
Night-vision - Visible light - Human being - Automobile - Forward looking infrared

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Smoke is more transparent to infrared than to visible light, so fire fighters use infrared imaging equipment when working in smoke-filled areas.

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Other Imaging

In infrared photography, infrared filters are used to capture only the infrared spectrum. Digital cameras often use infrared blockers. Cheaper digital cameras and some camera phones which do not have appropriate filters can "see" infrared, appearing as a bright white colour (try pointing a TV remote at your digital camera). This is especially pronounced when taking pictures of subjects near bright areas (such as near a lamp), where the resulting infrared interference can wash out the image.

Related Topics:
Infrared photography - Infrared filters - Digital camera - Blockers - Camera phones

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Thermography

Infrared radiation can be used to remotely determine the temperature of objects (if the emissivity is known). This is termed thermography, or in the case of very hot objects in the NIR or visible it is termed pyrometry. Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the public market in the form of infrared cameras on cars due to the massively reduced production costs.

Related Topics:
Emissivity - Thermography - Pyrometry

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Heating

Infrared radiation is used in Infrared saunas to heat the sauna's occupants and to remove ice from the wings of aircraft (de-icing).

Related Topics:
Infrared sauna - Aircraft

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Communications

IR data transmission is also employed in short-range communication among computer peripherals and personal digital assistants. These devices usually conform to standards published by IrDA, the Infrared Data Association. Remote controls and IrDA devices use infrared light-emitting diodes (LEDs) to emit infrared radiation which is focused by a plastic lens into a narrow beam. The beam is modulated, i.e. switched on and off, to encode the data. The receiver uses a silicon photodiode to convert the infrared radiation to an electric current. It responds only to the rapidly pulsing signal created by the transmitter, and filters out slowly changing infrared radiation from ambient light. Infrared communications are useful for indoor use in areas of high population density. IR does not penetrate walls and so does not interfere with other devices in adjoining rooms.

Related Topics:
Personal digital assistant - IrDA - Light-emitting diode - Lens - Modulated - Data - Silicon - Photodiode - Current

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Free space optical communication using infrared lasers can be a relatively inexpensive way to install a Gigabit/s communications link in urban areas, compared to the cost of burying fibre optic cable.

Related Topics:
Free space optical - Infrared laser - Fibre optic

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Infrared lasers are used to provide the light for optical fibre communications systems. Infrared light with a wavelength around 1330 nm (best transmission) or 1550 nm (least dispersion) are the best choices for standard silica fibres.

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Spectroscopy

Infrared radiation spectroscopy is the study of the composition of (usually) organic compounds, finding out a compound's structure and composition based on the percentage transmittance of IR radiation through a sample. Different frequencies are absorbed by different stretches and bends in the molecular bonds occurring inside the sample. Carbon dioxide, for example, has an absorption band at 4.2µm.

Related Topics:
Spectroscopy - Organic compound - Carbon dioxide

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