Infrared is a form of light, light that we can't see with our eyes, but that we can sometimes feel on our skin as heat. Infrared light is the same as the light that we can see except that the wavelength is longer and outside the range that our eyes can sense.
Infrared energy is emitted or absorbed by molecules when they change their rotational-vibrational movements. Infrared energy excites vibrational modes in a molecule through a change in the dipole moment, making it a useful frequency range for study of these energy states for molecules of the proper symmetry. Infrared spectroscopy examines absorption and transmission of photons in the infrared energy range.
Infrared is used in a variety of wireless communications, monitoring, and control applications. A few of the applications include home-entertainment remote-control boxes, HVAC (heating, ventilating, air conditioning), wireless local area networks, links between notebook computers and desktop computers, cordless modems, intrusion detectors, motion detectors, fire sensors, spectroscopy and weather forecasting.