Every object above absolute zero emits infrared radiation, enabling infrared sensors to 'see in the dark' by capturing heat signatures where visible light is scarce or absent.
Infrared imaging also excels at detecting heat sources even in well-lit conditions. From infrared thermometers measuring body or object temperatures to essential tools for police, security, and military operations—like weapon sights, vehicles, missiles, and satellites—all rely on proven infrared sensing technology.
Infrared sensors detect radiation in the infrared spectrum, spanning wavelengths from 700 nm to 1 millimeter (frequencies from a few hundred GHz to over 400 THz), bridging visible light and microwaves.
The signal chain processes this analog data in two primary ways: shifting it to visible wavelengths for human viewing (as in astronomy, where we perceive infrared as color-shifted images) or directly driving actuators (such as missile guidance systems).
Near-infrared (700 nm to 2.5 μm) sits just beyond human vision, while mid- and far-infrared extend to 1 mm. Far-infrared detection needs no external light, as all objects above absolute zero naturally glow in this range. Near-infrared observation often requires dedicated sources like LEDs or filtered bulbs.
Near-infrared sensors are far more affordable than passive far-infrared ones, some of which—like those in astronomy—are cooled with liquid nitrogen to suppress self-generated noise.
Classic TV remotes emit near-infrared pulses around 950 nm via inexpensive LEDs, encoding brand-specific commands. Receivers decode them, though fluorescent or neon lights can interfere, limiting range.
Infrared-sensing automatic trash cans place transmitter and receiver side-by-side. The constant modulated emission reflects off approaching objects, triggering the lid while conserving battery life.
Non-contact thermometers gauge infrared emissions from bodies or objects, applying Planck's law adjusted for emissivity to estimate temperature from blackbody ideals to real-world graybody measurements. Practical models use proportional approximations and sensor calibration for reliable results in everyday ranges.
Heat-seeking missiles have targeted infrared emissions from jet engines since the 1950s. Military infrared imaging satellites have monitored Earth for rocket and missile launches since the early 1960s.
Infrared thermography helps detect landmines buried just centimeters underground by revealing subtle thermal patterns under ideal conditions.
Night vision systems for vehicles or fixed surveillance combine near-infrared sensors with powerful illuminators to monitor areas in total darkness.
However, helmet- or weapon-mounted night vision prioritizes stealth, passively amplifying ambient visible light rather than emitting detectable infrared.
