Electromagnetic energy, invisible to the human eye, thats found at the red end of the spectrum. Hence the name - infra (below) red.
Certain types of film are sensitive to certain wavelengths of infrared energy. Infrared energy is also used by many common control systems in cameras. For example, point and shoot cameras sometimes send out invisible beams of infrared energy for their active focus systems. Remote controllers for cameras (and stereos and TV sets) often use coded pulses of infrared energy.
Infrared energy is often referred to as infrared light. Many people argue that this term is incorrect since IR cannot be seen by human eyes and light can be. However, its a useful concept. Photographically-detectable infrared energy - though not visible to humans - can still be affected by optical systems, unlike other forms of electromagnetic radiation such as gamma rays or radio waves. So from a photographic point of view, infrared light is a handy reminder of the optical qualities of this type of energy.
cf. electromagnetic radiation, infrared film, light, ultraviolet, wavelength.
Entry last updated 2002-04-10. Term 644 of 1487.
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