| A night vision is an optical equipment designed to see,
by biological or technological means, an object in a dark environment
Generations
When discussing night vision technology, you need to know about its
technology generations.
- The earliest products (1950's) The earliest night
vision scopes were based on image coversion, rather than intensification.
They required a source of invisible infrared (IR) light mounted on
or near the device to illuminate the target area.
- Generation 1 - The "starlight scopes"
of the 1960's (Vietnam Era) have three image intensifier tubes connected
in a series. These systems are larger and heavier than Gen 2 and Gen
3. The Gen 1 image is clear at the center but may be distorted around
the edges. (Low-cost Gen 1 imports are often mislabeled as a higher
generation.
- Generation 2 - The microchannel plate (MCP) electron
multiplier prompted Gen 2 development in the 1970s. The "gain"
provided by the MCP eliminated the need for back-to-back tubes - thereby
improving size and image quality. The MCP enabled development of hand
held and helmet mounted goggles.
- Generation 3 - Two major advancements characterized
development of Gen 3 in the late 1970s and early 1980s: the gallium
arsenide (GaAs) photocathode and the ion-barrier film on the MCP.
The GaAs photocathode enabled detection of objects at greater distances
under much darker conditions. The ion-barrier film increased the operational
life of the tube from 2000 hours (Gen 2) to 10,000 (Gen 3), as demonstrated
by actual testing and not extrapolation.
- Generation 4 - See the Night Vision Equipment Expert
Blog for a good explanation of this commonly misunderstood advancement
in night vision technology.
Spectral Range and Intensity Range
Night vision is made possible by a combination of two approaches:
sufficient spectral range, and sufficient intensity range.
- The spectral range techniques make the viewer sensitive to types of
light that would be invisible to humans. 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
sources of electromagnetic radiation (such as near-infrared or ultraviolet
radiation).
- The intensity range 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 evolved better night vision through the use of a larger
optical aperture, improved retina composition that can detect weaker
light over a larger spectral range, more photoefficient optics in the
eye, and improved neurological filtering. Enhanced intensity range is
achieved via technological means through the use of an image intensifier,
gain multiplication CCD, or other very low-noise and high-sensitivity
array of photodetectors.
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