Humans see light that includes a range of colors from red to violet, or purple, with each color equivalent to a wavelength or frequency of light. There are wavelengths that human eyes cannot see, including long wavelengths below red called infrared (IR), and short wavelengths above violet called ultraviolet (UV). Cameras have been developed to detect these different frequencies, and create viewable images. Infrared light can be viewed with an IR thermal camera, which detects infrared heat from objects.
Warm objects create heat that radiates, or sends out, infrared frequencies in all directions. An IR thermal camera can collect these frequencies and convert them to images that show a black-and-white or what is called a false-color image. False-color uses software to show different colors for levels of heat radiated from objects. Thermal cameras are widely used for energy surveys of buildings, where an IR camera shows the heat image of a building exterior that can detect leaking doors and windows, or areas of poor insulation.
People and animals also radiate infrared heat, which can be used for motion detecting equipment. Security systems can use infrared cameras that sense IR and send an alarm when movement is detected. Motion security systems can use IR thermal camera technology that can show video images of buildings or property at night. Some of these systems are passive, and only detect the IR energy sent out by objects. Many systems are active and use IR light-emitting diodes (LEDs) to send IR energy out that is reflected from objects and picked up by the cameras.
IR thermal camera technology is often used in space satellites to detect weather systems. The satellites, orbiting hundreds of miles or kilometers above the earth, detect light and heat radiation from weather patterns and storms and transmit the images to antennas on the ground. Weather companies can process false-color images of the weather using both visible and invisible light. IR systems are very good at showing differences in cloud heights from their temperatures, which can show the intensity of storms even at night.
Digital camera technology can detect IR energy directly, but camera film can also be used to take infrared pictures. The film contains an emulsion, or chemical layer, that is sensitive to the infrared frequencies. Infrared photography can be used for very low light conditions, or for special effects using light not normally visible to humans.
In the late 20th century, automotive designers began to include active IR thermal camera technology in cars and trucks for improved night vision. The systems send an IR frequency out from the front of the vehicle, and an IR camera collects any reflected energy in addition to any IR from people, animals or other vehicles. A heads-up display can show the image on a screen directly in the driver's field of view, which is a technology adapted from military aircraft displays.
IR thermal imaging is also used by the military and law enforcement for night vision. Cameras can be installed on aircraft in rotating pods and pointed in different directions by a pilot or crew member. Hand-held infrared cameras can help personnel on the ground by detecting IR heat sources for search and rescue or military missions.