Night vision technology allows people to see in the dark. Modern systems work surprisingly well, and some can operate in complete darkness. Most night vision systems rely on one of two basic technologies: thermal imaging and image intensifiers.
Thermal-based night vision systems, rely on the upper portion of the infrared light spectrum which is not visible to the human eye. In general, hot objects emit more infrared light than colder ones. Infrared sensors scan the environment and detect the objects that are emitting more infrared radiation. This data is then converted into images that are presented to the viewer. Since thermal-based systems do not rely on light, they can generate visible images in complete darkness.
Image intensifiers operate by intensifying visible light. They require a minimal amount light to work and are useless in complete darkness; this usually isn't a problem because the light provided by stars alone is sufficient. These systems simply amplify the light presented to a viewer and thereby make dark environments visible.
Night vision systems can complement all sorts of devices from telescopes to binoculars to still and video cameras. Perhaps the most popular applications of this technology is night vision goggles. Night vision goggles provide people with real-time images and therefore allow them to operate in dark environments.