The temperature-sensitive nerve endings in our skin can detect the difference between inside body temperature and outside skin temperature. Shorter, near infrared waves are not hot at all - in fact you cannot even feel them. These shorter wavelengths are the ones used by your TV's remote control.
Humans, at normal body temperature, radiate most strongly in the infrared at a wavelength of about 10 microns. A micron is the term commonly used in astronomy for a micrometer or one millionth of a meter. This image which is courtesy of the Infrared Processing and Analysis Center at CalTech , shows a man holding up a lighted match!
Which parts of this image do you think have the warmest temperature? How does the temperature of this man's glasses compare to the temperature of his hand?
To make infrared pictures like the one above, we can use special cameras and film that detect differences in temperature, and then assign different brightnesses or false colors to them. This provides a picture that our eyes can interpret. The orange areas are the warmest and the white-blue areas are the coldest. This image gives us a different view of a familiar animal as well as information that we could not get from a visible light picture.
Special sensors, like those aboard the Landsat 7 satellite, record data about the amount of infrared light reflected or emitted from the Earth's surface. This makes infrared light useful for electrical heaters and for cooking food. All objects emit infrared light. The human eye cannot see this light, but infrared cameras can detect it.
Visible light is the light we can see, so is used in photography and illumination. It is also used in fibre optic communications, where coded pulses of light travel through glass fibres from a source to a receiver. Radio waves, microwaves, infrared and visible light The behaviour of an electromagnetic EM wave in a substance depends on its frequency.
Radio waves Radio waves are used for communication such as broadcasting television and radio, communications and satellite transmissions. Microwaves Microwaves are used for cooking food, communications and for satellite communications. Microwaves - Higher High frequency microwaves have frequencies which are easily absorbed by molecules in food.
Infrared Infrared IR light is used by electrical heaters, cookers for cooking food, short-range communications like remote controls, optical fibres, security systems and thermal imaging cameras which detect people in the dark.
Infrared - Higher Infrared light has frequencies which are absorbed by some chemical bonds. Within the electromagnetic spectrum, infrared waves occur at frequencies above those of microwaves and just below those of red visible light, hence the name "infrared. Similar to the visible light spectrum, which ranges from violet the shortest visible-light wavelength to red longest wavelength , infrared radiation has its own range of wavelengths.
The shorter "near-infrared" waves, which are closer to visible light on the electromagnetic spectrum, don't emit any detectable heat and are what's discharged from a TV remote control to change the channels.
The longer "far-infrared" waves, which are closer to the microwave section on the electromagnetic spectrum, can be felt as intense heat, such as the heat from sunlight or fire, according to NASA. IR radiation is one of the three ways heat is transferred from one place to another, the other two being convection and conduction. Everything with a temperature above around 5 degrees Kelvin minus degrees Fahrenheit or minus degrees Celsius emits IR radiation. The sun gives off half of its total energy as IR, and much of the star's visible light is absorbed and re-emitted as IR, according to the University of Tennessee.
Household appliances such as heat lamps and toasters use IR radiation to transmit heat, as do industrial heaters such as those used for drying and curing materials. Incandescent bulbs convert only about 10 percent of their electrical energy input into visible light energy, while the other 90 percent is converted to infrared radiation, according to the Environmental Protection Agency.
Infrared lasers can be used for point-to-point communications over distances of a few hundred meters or yards. The receiver converts the light pulses to electrical signals that instruct a microprocessor to carry out the programmed command.
One of the most useful applications of the IR spectrum is in sensing and detection. All objects on Earth emit IR radiation in the form of heat. This can be detected by electronic sensors, such as those used in night vision goggles and infrared cameras.
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