Infrared imaging is a technique used to detect radiation or heat patterns in the long-infrared range of the EM spectrum (roughly 9,000–14,000 nanometers) and produce images of that radiation, called thermograms. Since infrared radiation is emitted by all objects with a temperature above absolute zero (- 273.15 °C), thermography makes it possible to see with or without visible light. The amount of radiation emitted by an object increases with temperature. When viewed through a thermal imaging camera, warm objects stand out well against cooler backgrounds; humans and other warm-blooded animals become easily distinguishable from their environments, day or night. As a result, thermography is particularly useful to the military and for surveillance purposes.
Many things besides people and animals emit infrared light - the Earth, the Sun, far away stars, and galaxies do also! As solar radiation hits the Earth, some of this energy is absorbed by the atmosphere and the surface, thereby warming the planet. This heat is emitted from Earth in the form of infrared radiation.
VISIBLE LIGHT WAVES
Humans are blind to many wavelengths of light. Visible light waves are the only electromagnetic waves that we can see. We see these waves as the colours of the rainbow (red, orange, yellow, green, cyan, blue, violet). Each colour
has a different wavelength, ranging from 700 (red) to 400 (violet) nanometers. Our eyes contain specialized cells, called cones, that allow us to differentiate this narrow range of wavelengths.