infrared radiation

Electromagnetic radiation of wavelength between about 700 nanometres and 1 millimetre – that is, between the limit of the red end of the visible spectrum and the shortest microwaves. All bodies above the absolute zero of temperature absorb and radiate infrared radiation. Infrared radiation is used in medical photography and treatment, and in industry, astronomy, and criminology.

The human eye cannot detect infrared radiation, but its effects can be demonstrated. For example, an electric hob at a high temperature glows and is hot. As it cools down, it no longer gives out visible light. However, the heat (infrared radiation) that continues to be given out can be felt. Infrared absorption spectra are used in chemical analysis, particularly for organic compounds. Objects that radiate infrared radiation can be photographed on specially sensitized emulsions or made visible in the dark by infrared-sensitive electronic detectors. This is important for military purposes and in detecting people buried under rubble.