Infrared (IR) radiation is electromagnetic energy that has the same form as visible light but has wavelength greater than about 700 nm and is not detected to any appreciable degree by photoreceptors. Natural objects radiate such energy approximately in proportion to the fourth power of their absolute temperature in accordance with the Stephan Boltzman law of black body radiation. Animals that are warmer or colder than their surroundings can be thought of as infrared (3–20 μm wavelength) luminous sources that are respectively brighter or darker than the background against which they are observed. Reptiles (and perhaps bats and insects) have evolved sense organs that are responsive to infrared radiation of the intensities radiated by objects and animals in the natural world, and thus may mediate a specialized infrared sense. Mammals, including primates, have skin sensory receptors that respond to warmth and thus to infrared radiation; however, their sensitivity is such that only objects that are very warm (such as fire or the sun) or nearby are detected via their IR radiation. Such receptors are discussed under Thermoreceptors.
KeywordsInfrared Radiation Black Body Radiation Optic Tectum Primary Afferents Infrared Sense
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