Night Vision Googles
Human vision is confined to a small portion of the electromagnetic spectrum called visible light. Enhanced spectral range allows the viewer to take advantage of non-visible source of electromagnetic radiation (such as infrared radiation or near-UV).
It is simply the ability to see with very small quantities of light. Although the human visual system can, in theory, detect single photons under ideal conditions, the neurological noise filters limit sensitivity to a few tens of photons, even in ideal conditions.
Some animals have developed better vision with the use of a larger optical aperture, the improved composition of the retina that can detect a faint light over a larger spectral range, more fotoeficiente optics in the eye, and improved neurological filtering that is more tolerant of noise.
Enhanced intensity range is achieved via technological means using an image intensifier, the gain multiplier or CCD array or other very low noise and high sensitivity photodetectors. Night vision biological rhodopsin molecules eye rods undergo a change in shape while the light is absorbed by them. The maximum time accumulation rhodopsin for optimal viewing of the night in humans is of 30 minutes.
Rhodopsin in the human rods is insensitive to red wavelengths of light longer, so many people use red light to preserve night vision and will not drain the eye rhodopsin stores in the rods and instead is viewed by the cones.
Some animals, such as cats, dogs, and deer, have a structure called the tapetum lucidum in the back of the eye that reflects light for even better night vision than humans, in whom only 10% of the Light entering the eye falls photosensitive parts of the retina.
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