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Night vision is making possible to see at night. This can be possible by two ways, they are: technically and biologically.
Biologically: Rhodopsins are the rods of the eye that expands as light enters into the eye. The peak rhodopsin build up time for optimal night vision in humans is 30 minutes. Rhodopsin in the human rods isn't sensitive to the longer red wavelengths of light, so many people use red light to preserve night vision as it will not deplete the eye's rhodopsin stores in the rods and instead is viewed by the cones. In cases of animals like dogs and cats, tapetum (special structure) presents at the back of the eye. If reflects light for even better night vision than humans.
In case of some snakes, biological night vision is that of detecting thermal emissions from a heat source. In fact, it is not the night vision, but rather a system of thermo sensitive pits in their face that can detect the amount of heat and the distance to the heat source.
Making night vision possible technological is different. It works on one of two principles. The first is by detecting infrared radiation, which is a form of energy emitted by all objects regardless of the ambient light conditions. A device based on this principle is called an infrared camera. The second is by intensifying the small amount of light present even at night, from the stars and the moon. A device based on this principle is called an image intensifier or starlight scope (SLS).
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