Infrared (IR) light is a form of electromagnetic radiation with a wavelength longer than that of red light, just beyond the visible spectrum. Despite the fact that it cannot be perceived by the human eye, there are many different uses of infrared in a wide variety of fields. Uses include night vision technology, visualization of temperature difference, heating, infrared astronomy, and remote control. This wide array of uses means that infrared is used for military applications and in fields as diverse as medicine and astronomy. Infrared emitters and receivers are, because of their wide prevalence and usefulness, quite common and generally inexpensive.
One of the most common uses of infrared radiation is night vision, a technology that aims to maintain and clarify vision in the absence of visible light. Infrared light can be used in a variety of different ways to allow one to see in the absence of visible light. For instance, objects that release heat also release infrared radiation, so some forms of night vision are based on visualizing and navigating based on temperature differences in the environment. Other forms actively project infrared light into the environment. The environment can be visualized with devices that pick up the infrared light and project an image in the visible spectrum on a screen or other viewing device.
Remote determination of temperature differences is another of the common uses of infrared light. All objects emit some amount of infrared radiation that varies based on temperature, so comparison of the emitted radiation can be used to visualize and compare temperature. This can be used in medicine to examine locations of high and low temperatures in an individual's body. It can also be used for night vision purposes, though this can be difficult in environments with only limited temperature variance. It is often used in industry as well, particularly to search for defective sections of pipes or to remotely examine areas that are inaccessible because of various health concerns.
Many of the most common uses of infrared radiation are in the area of electronics, as infrared light can be used to transmit signals and data over small spaces. Remote controls, for instance, commonly use infrared light to transmit signals for controlling devices such as televisions and other household electronics. It is particularly useful for this purpose because the signal is generally unable to penetrate walls. Infrared signals used in one room or building are, therefore, generally unable to interfere with devices in other rooms or buildings.