The temperature of the object is directly related to the frequency of the light that it emits. At room temperature bodies emit infrared light, but as the temperature increases past a few hundred degrees Celsius, bodies start to emit at visible frequency, from red, through orange, yellow, and white before ending up at blue, beyond which the emission includes increasing amounts of ultraviolet.
Also the amount of radiation emitted by an object increases with temperature difference between the object and its surroundings .
Infrared radiation emitted by an object can be therefore be used to determine the temperature of objects from a distance away. This is called thermography.
Thermography (thermal imaging) is mainly used in military and industrial applications but the technology is reaching the general public nowadays in the form of infrared cameras due to the massively reduced production costs.
Infrared radiation is emitted by all objects based on their temperatures and thermography makes it possible to "see" one's environment with or without visible illumination. A 'false-colour' images is made up by filling in a contour map of temperature boundaries with visible colour.
Hot water in a cold water cup - shows convection...
Infrared (thermal) images of homes that were inspected using infrared cameras - this can be used to spot 'heat leaks'.
Thermal Imaging Demonstration - New York Firefighters - safety device
Welcome to night vision... this is NOT infra-red thermal imaging. It is achieved by image intensifiers which convert low level visible light into images of high enough intensity for us to see. This can involve using Infrared in night vision equipment when there is insufficient visible light to see. Night vision devices operate through a process involving the conversion of ambient light photons into electrons which are then amplified by a chemical and electrical process and then converted back into visible light. Infrared light sources can be used to increase the available ambient visible light for night vision devices, increasing in-the-dark visibility without actually using a visible light source.These are often incorporated in goggles or binoculars and are often used by the military and police services. Note that the people's faces look 'normal' but green - whereas IR cameras show the temperature differences in the face by making a contour picture in different colours.
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