Night vision

Night Vision

Night vision (/naɪt ˈvɪʒən/) is the ability to see in low-light conditions. Whether by biological or technological means, night vision is made possible by a combination of two approaches: sufficient spectral range, and sufficient intensity range.

Etymology

The term "night vision" comes from the ability to see during the nighttime, when light is scarce. The term is derived from the Old English 'niht' (night) and the Latin 'visio' (sight).

Biological Night Vision

Many animals have the ability to see in the dark, thanks to some special adaptations. These adaptations include larger eyes, a larger number of rod cells in the retina, a tapetum lucidum which reflects light back through the retina, and an increased use of the rod cells over the cone cells.

Rod cells are photoreceptor cells in the retina of the eye that can function in less intense light than the other type of visual photoreceptor, cone cells. Rods are usually found concentrated at the outer edges of the retina and are used in peripheral vision.

Cone cells, or cones, are one of the two types of photoreceptor cells that are in the retina of the eye which are responsible for color vision as well as eye color sensitivity; they function best in relatively bright light.

Tapetum lucidum is a layer of tissue in the eye of many vertebrates. Lying immediately behind the retina, it reflects visible light back through the retina, increasing the light available to the photoreceptors.

Technological Night Vision

Technological night vision is achieved through the use of devices that amplify the available light, such as night vision devices or thermal imaging.

Night vision devices (NVDs) are optoelectronic devices that allow 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.

Thermal imaging is a method of improving visibility of objects in a dark environment by detecting the objects' infrared radiation and creating an image based on that information.

Related Terms

• Infrared
• Photoreceptor cell
• Retina
• Low-light level television

External links

• Medical encyclopedia article on Night vision
• Wikipedia's article - Night vision

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