All bodies radiate infra red radiation, also called thermal radiation because warm or hot bodies radiate the most. Infra – red can be used to detect warm objects because in the infra -red part of the spectrum, they appear much brighter than their surroundings. They can be used by the rescue services to detect people – possibly unconscious - trapped in smoke filled buildings or by a collapsed building after an earthquake, or by the police to detect suspected criminals hiding at night.
Infra – red images called thermographs can also be used by doctors to detect disease. If a patient has circulation problems, blood circulation will be poor in certain parts of the body, and these parts will show up poorly in the infra red. The left leg of the patient below may have circulation problems.
If a patient has cancer or arthritis, the affected area will show up brightly in the infra – red. The thermograph below shows a woman in the early stages of breast cancer.
Astronomers take infra red images of stars to find their temperature, and burglar alarms are sensitive in the infra red part of the spectrum to detect intruders.
Of course, people do not look at a raw infra – red image – infra red is invisible to the human eye. The radiation is processed so that warmer parts appear red and cooler parts appear blue.