Night vision device

A night vision device, abbreviated as NVD, is an optical instrument that allows images to be produced in levels of light approaching total darkness. They are most often used by the military and law enforcement agencies, but are available to civilian users.

Operation
Night vision can work in two very different ways, depending on the technology used.
 * Image enhancement: This works by collecting the tiny amounts of light, including the lower portion of the infra-red light spectrum, that are present but may be imperceptible to our eyes, and amplifying it to the point that we can easily observe the image.
 * Thermal imaging: This technology operates by capturing the upper portion of the infra-red light spectrum, which is emitted as heat by objects instead of simply reflected as light. Hotter objects, such as warm bodies, emit more of this light than cooler objects like trees or buildings.

In the Halo universe
The SRS99 series are equipped with night vision scopes. These features are only accessible to players in Halo: Combat Evolved and Halo: Reach.

All versions of the MJOLNIR Powered Assault Armor possess night vision and infrared enhancements. However, they are unavailable in the course of most of the games, with the exception of Halo: Reach.

Sangheili armor also has built-in night vision, albeit with a purple color rather than the usual green found in UNSC versions.