Night vision systems use infra-red image sensors to detect and produce image of objects that are difficult to see in the absence of sufficient visible light. There are two main categories of automotive night vision systems, active and passive. Active night vision systems use infrared light to illuminate the dark surroundings while the passive system relies on thermal radiation emitted by human beings, animals and any other objects at a temperature different from the ambient.
Active night vision systems operate at infrared wavelengths near the visible spectrum (0.7 - 3.0 μm). They have their own infrared light source that illuminates the objects at a significant distance ahead on the road where the headlights cannot reach. The reflected infrared light is captured by infrared cameras. Some systems use a constant light source, while others use pulsed infrared light. Active night vision systems provide clear monochromatic images of the road ahead and its surroundings.
Passive night vision systems operate at longer infrared wavelengths than active systems (8 - 12 μm). They detect the thermal radiation emitted by humans and animals using thermographic cameras. They are not capable of detecting obstacles at the ambient atmospheric temperature. Passive systems can generally detect objects at longer distances compared to active systems and are better at seeing through fog.
Automotive Night Vision Demonstration: Clemson AuE893 Class Project by Fan Zeng