Infrared (IR) light is a wavelength of energy that is invisible to the human eye. The most common source of this energy is heat; objects can have their relative temperatures measured by how much of this energy they give off. Lower wavelengths or "near infrared" — closest to the visible light color red — are not hot, and are often used to transmit data in electronics. A remote control, for example, may use a particular wavelength of near infrared to communicate with a receiver, sending pulses of light that transmit a signal to the device, telling it what to do.
Description and Measurement
A form of energy, IR is part of the electromagnetic spectrum. This spectrum is comprised of radio waves; microwaves; infrared, visible, and ultraviolet light; x-rays; and gamma rays. Each form of energy is ordered by wavelength; infrared falls between microwaves and visible light waves because its waves are shorter than microwaves but longer than those of visible light.
The prefix infra comes from the Latin word which means "below;" the term means "below red," indicating its position in the electromagnetic spectrum. Visible light has a range of wavelengths that are manifested in the seven colors of the rainbow; red has the longest wavelength and violet has the shortest. Infrared, with wavelengths longer than the color red, is invisible to the human eye.
Just like with visible light, there are a range of wavelengths of IR. The International Commission on Illumination has divided it into three general sections based on the length of the wave and density. These groups are commonly known as near, medium, and far infrared, with near infrared being nearest to the visible light side of the spectrum and far, or long-wave, being close to the microwave zone. There are uses for IR wavelengths in each group, from wireless communication to acting as heat source.
Nearly all objects emit heat or energy, and one of the most easily discernible forms of energy is infrared. When an object is not hot enough to give off visible light, it emits most of its energy in the IR spectrum. It is this heat that affords IR many applications in almost every sector of life, including health, science, industry, art, and entertainment.
Converting infrared energy, also known as radiant heat, into an image that the human eye can see and understand is done with a process called thermal imaging. An IR camera is used to accurately measure the temperature of an object, which is then translated into color. For example, infrared imaging typically shows the warmest areas in a human body as red, followed by yellow, green, blue, and violet as the temperature decreases. By studying how body heat is distributed, thermal imaging can health professionals to analyze body tissue and fluid to detect injury or disease.
Infrared light is used in night vision equipment, allowing the user to see in the dark. Two types of night vision both use IR: thermal and image-intensifying. Thermal night vision allows the user to recognize people and objects by the heat pattern they emit. Intensifiers amplify existing light — including infrared — to allow the user to see.
As a way to measure temperature, IR is used in many different types of applications. The military uses infrared sensors to locate and track targets or to detect hidden land mines or arms caches. Sensors on satellites are used for environmental monitoring, pinpointing areas of pollution, fire, or deforestation. Search and rescue operations use IR extensively to locate missing persons lost in the forest or jungle, as well as in collapsed buildings or at the site of other disasters.
Many remote control devices in homes use infrared. These remotes use this type of light to carry signals between a remote control transmitter and the device it's commanding. The transmitter sends out light in pulses, which are translated into binary codes that have corresponding commands. The receiver is positioned on the front of the device, where it receives these pulses of light and decodes them into binary data, which is understood by the microprocessor inside the apparatus.
Many different types of scientists use infrared in their work, from astronomers use it to learn more about galaxies light years away to archaeologists who use it when studying ancient settlements. Infrared is being used to preserve, restore, and conserve valuable historical and artistic works as well; the invisible details of ancient fragments and images painted under paintings are being brought to light through the use of IR technology. In industry, thermal imaging is invaluable in testing and monitoring mechanical systems.