1. Night vision
From Wikipedia, the free encyclopedia
For other uses, see Night vision (disambiguation).
Two American soldiers pictured during the2003 Iraq War seen through an image intensifier
Night vision 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. Humans have poor night vision compared to many animals, in part because
the human eye lacks atapetum lucidum.[1]
Contents
[hide]
1 Types of ranges
o 1.1 Spectral range
o 1.2 Intensity range
2 Biological night vision
3 Night vision technologies
4 Night vision goggles
5 Active infrared
6 Laser range gated imaging
7 Thermal vision
8 Image intensifier
9 Night vision devices
10 Automotive night vision
11 See also
12 Patents

2. 13 References
14 External links
[edit]Types of ranges
[edit]Spectral range
Night-useful spectral range techniques can sense radiation that is invisible to a human observer.
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). Some animals can see using
much more of the infrared and/or ultraviolet spectrum than humans.
[edit]Intensity range
Sufficient intensity range is simply the ability to see with very small quantities of light. [2]
Many animals have better night vision than humans do, the result of one or more differences in the
morphology and anatomy of their eyes. These include having a larger eyeball, a larger lens, a larger
optical aperture (the pupils may expand to the physical limit of the eyelids), more rods than cones (or
rods exclusively) in the retina, and a tapetum lucidum.
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.
[edit]Biological night vision
For more details on this topic, see Adaptation (eye).
In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in shape as
they absorb light. Rhodopsin is the chemical that allows night-vision, and is extremely sensitive to light.
Exposed to a spectrum of light, the pigment immediately bleaches, and it takes about 30 minutes to
regenerate fully, but most of the adaptation occurs within the first five or ten minutes in the dark.
Rhodopsin in the human rods is less sensitive to the longer red wavelengths of light, so traditionally
many people use red light to help preserve night vision as it only slowly depletes the eye's rhodopsin
stores in the rods and instead is viewed by the cones. However the US submarine force ceased using
red lighting for night adaptation after studies found little significant advantage of using low level red
over low level white lighting.[3]
Many animals have a tissue layer called the tapetum lucidum in the back of the eye that reflects light

3. back through the retina, increasing the amount of light available for it to capture. This is found in
many nocturnal animals and some deep sea animals, and is the cause of eyeshine. Humans lack a
tapetum lucidum.
Nocturnal mammals have rods with unique properties that make enhanced night vision possible. The
nuclear pattern of their rods changes shortly after birth to become inverted. In contrast to
contemporary rods, inverted rods have heterochromatin in the center of their nuclei
and euchromatin and other transcription factors along the border. In addition, the outer nuclear
layer (ONL) in nocturnal mammals is thick due to the millions of rods present to process the lower light
intensities of a few photons. Rather than being scattered, the light is passed to each nucleus
individually.[4] In fact, an animal's ability to see in low light levels may be similar to what humans see
when using first- or perhaps second-generation image intensifiers.[citation needed]
A larger size of pupil relative to the rest of the eye, also aids night vision. [citation needed]
[edit]Night vision technologies
Film about the development of military night vision technology
Night vision technologies can be broadly divided into three main categories:
Image intensification
Image intensification technologies work on the principle of magnifying the amount of received
photons from various natural sources such as starlight or moonlight. Examples of such
technologies include night glasses and low light cameras.
Active illumination
Active illumination technologies work on the principle of coupling imaging intensification
technology with an active source of illumination in the near infrared (NIR) or shortwave
infrared (SWIR) band. Examples of such technologies include low light cameras.
Thermal imaging

4. Thermal imaging technologies work by detecting the temperature difference between the
background and the foreground objects. Some organisms are able to sense a crude thermal
image by means of special organs that function as bolometers. This allows thermal infrared
sensing in snakes, which functions by detection of thermal radiation.
[edit]Night vision goggles
This section does
not cite anyreferences or
sources. (May 2012)
Binoculars (night vision goggles on flight helmet) Note: the green color of the objective lenses
is the reflection of the Light Interference Filters, not a glow.
Night glasses are telescopes or binoculars with a large diameter objective. Large lenses
can gather and concentrate light, thus intensifying light with purely optical means and
enabling the user to see better in the dark than with the naked eye alone. Often night
glasses also have a fairly large exit pupil of 7 mm or more to let all gathered light into the
user's eye. However, many people can't take advantage of this because of the limited
dilation of the human pupil. To overcome this, soldiers were sometimes
issued atropine eye drops to dilate pupils.[when?] Before the introduction of image
intensifiers, night glasses were the only method of night vision, and thus were widely
utilized, especially at sea. Second World War era night glasses usually had a lens
diameter of 56 mm or more with magnification of seven or eight. Major drawbacks of
night glasses are their large size and weight.
[edit]Active infrared

5. Imaging results with (top) and without (bottom) active-infrared.
Active infrared night vision combines infrared illumination of spectral range 700–
1,000 nm (just below the visible spectrum of the human eye) with CCD cameras
sensitive to this light. The resulting scene, which is apparently dark to a human observer,
appears as a monochrome image on a normal display device.[5]
Because active infrared night vision systems can incorporate illuminators that produce
high levels of infrared light, the resulting images are typically higher resolution than other
night vision technologies.[6][7] Active infrared night vision is now commonly found in
commercial, residential and government security applications, where it enables effective
night time imaging under low light conditions. However, since active infrared light can be
detected by night vision goggles, there can be a risk of giving away position in tactical
military operations.
[edit]Laser range gated imaging
Laser range gated imaging is another form of active night vision which utilizes a high
powered pulsed light source for illumination and imaging. Range gating is a technique
which controls the laser pulses in conjunction with the shutter speed of the camera's
detectors.[8] Gated imaging technology can be divided into single shot, where the
detector captures the image from a single light pulse to multi-shot, where the detector
integrates the light pulses from multiple shots to form an image.

6. One of the key advantages of this technique is the ability to perform target recognition as
opposed to detection with thermal imaging.
[edit]Thermal vision
See also: thermographic camera and Forward_looking_infrared
Thermal imaging cameras are excellent tools for night vision. They detect thermal
radiation and do not need a source of illumination. They produce an image in the darkest
of nights and can see through light fog, rain and smoke. Thermal imaging cameras make
small temperature differences visible. Thermal imaging cameras are widely used to
complement new or existing security networks, and for night vision on aircraft, where
they are commonly referred to as "FLIR" (for "forward-looking infrared".)
[edit]Image intensifier
Main article: Image intensifier
The image intensifier is a vacuum-tube based device that converts invisible light from an
image to visible light so that a dimly lit scene can be viewed by a camera or the naked
eye. While many believe the light is "amplified," it is not. When light strikes a
chargedphotocathode plate, electrons are emitted through a vacuum tube that strike the
microchannel plate that cause the image screen to illuminate with a picture in the same
pattern as the light that strikes the photocathode, and is on a frequency that the human
eye can see. This is much like a CRT television, but instead of color guns the
photocathode does the emitting.
The image is said to become "intensified" because the output visible light is brighter than
the incoming IR light, and this effect directly relates to the difference in passive and
active night vision goggles. Currently, the most popular image intensifier is the drop-in
ANVIS module, though many other models and sizes are available at the market.
[edit]Night vision devices
Main article: Night vision device
A night vision device (NVD) is a device comprising an image intensifier tube in a rigid
casing, commonly used by military forces. Lately, night vision technology has become
more widely available for civilian use. For example, enhanced vision systems (EVS) have
become available for aircraft to help pilots with situational awareness and avoid
accidents. These systems are included in the latest avionics packages from
manufacturers such as Cirrus and Cessna.

7. A specific type of NVD, the night vision goggle (NVG) is a night vision device with dual
eyepieces. The device can utilize either one intensifier tube with the same image sent to
both eyes, or a separate image intensifier tube for each eye. Night vision goggle
combined with magnification lenses constitutes night vision binoculars. Other types
include monocular night vision devices with only one eyepiece which may be mounted to
firearms as night sights. NVG and EVS technologies are becoming more popular
products for helicopter operations to improve safety. The NTSB is considering EVS as
recommended equipment for safety features.