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Thermal Properties of Infrared Radiation

Infrared radiation can be absorbed and converted into thermal energy by most materials. The emission wavelength controls the amount of energy absorbed. Every organic material has specific wavelength bands at which it absorbs - and emits - best. When infrared radiation is absorbed by an object, changes occur in the object's molecules that affect the frequency and amplitude of their oscillation.

During the absorption process, the oscillation rate of the object's molecules rises to a higher energy level before returning to normal. During the returning stage, thermal energy is released in the form of heat. It is this thermal energy that warms objects during space and spot heating and has proved useful in a wide variety of industrial applications. This method of radiant heat transfer transmits energy to the receiver without heating the ambient air, in much the same manner that a microwave oven cooks food.

Each substance has an infrared absorption spectrum that is characteristic to it alone. Depending on the object, some wavelengths will be readily absorbed, others less so, and some wavelengths very little or not at all. The amount of infrared radiation striking an object that is actually absorbed depends on the absorptance of the surface. Surfaces that are good emitters are also good absorbers (the opposite also holds true). The incident energy that is not absorbed will either be transmitted or reflected.

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