21-03-2012, 02:04 PM
NIGHT VISION
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INTRODUCTION
Ability to see in a dark environment
Night vision is made possible by the combination of two approaches :
Sufficient spectral range
Sufficient intensity range
NIGHT VISION
Spectral Range - Human vision is confined to visible light portion of spectrum.
Enhanced spectral range allows the viewer to take advantage of non-visible portion of spectrum.
Intensity Range - Sufficient intensity range is the ability to see with very small quantity of light.
Enhanced intensity range can be achieved by the use of an image intensifier and an array of photodetectors.
BIOLOGICAL NIGHT VISION
Rhodopsin – the chemical that allows night vision and extremely sensitive to light.
Rhodopsin in human rods are less sensitive to red light.
Many animals have a tissue layer called the tapetum lucidum.
Nocturnal mammals have Inverted rods, consists of heterochromatin and euchromatin.
Large size of eye and large size of pupil relative to eye contribute to night vision.
ACTIVE INFRARED
Active infrared night vision combines infrared illumination of spectral range 700-1000nm.
The resulting scene appears as a monochrome image on a normal display device.
Because these systems can incorporate illuminators that produce high levels of infrared light.
The resulting images are typically higher resolution than other night vision technologies.
It is now commonly found in security applications because of effective night time imaging under low light conditions.