1. Introduction

The word ‘Night vision’ itself means the ability to see in low light conditions. Humans have poor

night vision compared to many other animals.So we all might have a question in our mind that is

this really possible to see in the dark night? The answer is most definitely yes. With the proper

night-vision equipment, you can see a person standing over 200 yards (183 m) away on a

moonless, cloudy night!. Originallydeveloped for military use, it has provided the United States

with a strategic militaryadvantage, the value of which can be measured in lives. Federal and state

agencies nowroutinely utilize the technology for site security, surveillance as well as search

andrescue. Night vision equipment has evolved from bulky optical instruments inlightweight

goggles through the advancement of image intensification technology.

The night has always had a mysterious and eerie aura to it, due to the darkness that it

accompanies. Through time, the dark has always been something that a lot of people fear. As

they say, you never know what lurks in the dark. However, as technology developed, the night

has become less of a scary monster and even became a sought after period of the day, all thanks

to the invention of the night vision. If you're wondering how this innovation started in the first

place, read on and learn the history of night vision.It has always been a point that man had to

dominate his enemies but at the same time making little damage as he can.

In the beginning, men fought at daytime since night raids were considered to be very dangerous.

They were and virtually impossible back then. With some time, men realized that surprising their

enemies with attacks were much effective and could be very devastating on their enemies' side.

This was the situation when torches became a hit, especially in the middle Ages. If a torch can

last longer, the better. However, brilliant may torches seem, it gave one big problem- it revealed

the position of the attacker.This problem was answered during the 1940's on the midst of World

War II, by the innovation of night vision. At first, it was only sniper riffles that had this

technology, so that they would have the ability to foresee enemies even from a distance. The use

of this gave a dramatic effect on the whole war's course. Ever since the Germans have found its

usefulness, they have begun developing innovative technology so that they can successfully

dominate even the night.it was during the 1960's Vietnam Era, when military troops began

developing night vision technology. It was this time when the night vision goggles first came out

and promoted. There was a remarkable advantage seen on those military divisions that has night

vision goggles compared to those that did not have them. This became the reason why the

government along with the military pushed on with further research about the said technology. In

terms of war, the technology was also used in the war against Iraq. It has proved to be an

extremely excellent tool, especially for defensive purposes and guarding against the militia. The

advantage is also present for thermal vision. Nonetheless, they can get the best of both worlds by

combining both thermal and night vision. Doing this gives overwhelming power over the night.

Nowadays, night vision technology is widely available even to the public. Most likely,

equipments with this feature are used by hunters since it is undeniably a reliable way for them to

detect animals even during night time.

Two technologies are used for night vision:-

(1)Thermal Imaging

This work by collection the tiny amounts of light including the lower portion of infrared light

spectrum that are present but may be imperceptible to your eyes, and amplifying it to the point

that we can easily observe the image.

(2)Image Enhancement

This technology operates by capturing the upper portion of the infrared light spectrum, which is

emitted as heat by the objects instead of simply reflected as light. Hotter object, such as warm

bodies, emit more of this light than cooler objects likes trees or buildings.

2. Types of Night Vision

There are two type night vision such as

2.1. Biological Night Vision

 In biological night vision, molecules of rhodopsin in the rods of the eye undergo a change in

shape as light is absorbed by them. The peak rhodopsin build-up time for optimal night vision in

humans is 30 minutes, but most of the adaptation occurs within the first five or ten minutes in the

dark. Rhodopsin in the human rods is insensitive 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.

.Some animals, such as cats, dogs, and deer, have a structure called tapetumlucidum in the back

of the eye that reflects light back towards the retina, increasing the amount of light it captures. In

humans, only 10% of the light that enters the eye falls on photosensitive parts of the retina. Their

ability to see in low light levels may be similar to what humans see when using first or perhaps

second generation image intensifiers

2.2. Technical Night Vision

A night vision device (NVD) is an optical instrument that allows images to be produced in levels

of light approaching total darkness. They are most often used by military and law enforce

agencies but are available to civilian users. In this technology various types of instruments are

used.Details descriptions of this technology is described in next page.

3. Working of Technical Night Vision

Night vision can works in two very different ways depending on the technology used. Before

discussing about the types of night vision technology first known basic things of light.

3.1. Light Basics

In order to understand thermal imaging, it is important to understand something about light. The

amount of energy in a light wave is related to its wavelength: Shorter wavelengths have higher

energy. Of visible light, violet has the most energy, and red has the least. Just next to the visible

light spectrum is the infrared spectrum.

Fig1:-Spectrum of light

Infrared light can be split into three categories:-

3.1.1. Near-infrared (near-IR)

Closest to visible light, near-IR has wavelengths that range from 0.7 to 1.3 microns, or 700

billionths to 1,300 billionths of a meter.

3.1.2. Mid-infrared (mid-IR)

Mid-IR has wavelengths ranging from 1.3 to 3 microns. Both near-IR and mid-IR are used by a

variety of electronic devices, including remote controls.

3.1.3. Thermal-infrared (thermal-IR)

Occupying the largest part of the infrared spectrum, thermal-IR has wavelengths ranging from 3

microns to over 30 microns.The key difference between thermal-IR and the other two is that

thermal-IR is emitted by an object instead of reflected off it. Infrared light is emitted by an object

because of what is happening at the atomic level.

Night vision can work in two very different ways, depending on the technology used.

3.2. Thermal Imaging

A special lens focuses the infrared light emitted by all of the objects in view. The focused light is

scanned by a phased array of infrared-detector elements. The detector elements create a very

detailed temperature pattern called a thermogram..

Fig2:-The basic of thermal imaging system

It only takes about one-thirtieth of a second for the detector array to obtain the temperature

information to make the thermogram. This information is obtained from several thousand points

in the field of view of the detector array. The thermogram created by the detector elements is

translated into electric impulses. The impulses are sent to a signal-processing unit, a circuit board

with a dedicated chip that translates the information from the elements into data for the display.

The signal-processing unit sends the information to the display, where it appears as various

colors depending on the intensity of the infrared emission. The combination of all the impulses

from all of the elements creates the image.

It is quite easy to see at day time But at night you can see very little

Thermal imaging lets you see again

Fig3:-Different view

There are two type of thermal imaging detector

3.2.1. Uncooled Detector

This the most common type of thermal imaging detector. The infrared elements are contained in

a unit that operates a room temperature. This type of system is completely quit and activate

immediately and the battery built right in.

3.2.2. Cooled Infrared Detector

More expensive and susceptible to damage from rugged used, these system has cooled inside a

container that cool them below zero c. These the of system can see more than 1000 ft(300m).

3.3. Image Intensifier

This method of night vision amplifies the available light to achieve better vision.Digram is given

below. A conventional lens capture the ambient light. This lens focuses available light (photons)

on the photocathode of an image intensifier tube.

Fig4:-Image intensifier process

The light energy causes electrons to be released from the cathode which are accelerated by an

electric field to increase their speed (energy level). These electrons enter holes in a micro

channel plate and bounce off the internal specially-coated walls which generate more electrons

as the electrons bounce through. This creates a denser “cloud” of electrons representing an

intensified version of the original image.Achannel using a process called cascaded secondary

emissions electrons pass through the micro- channels, they cause thousands of other electrons

to be released in each. Basically, the original electrons collide with the side of the channel,

exciting atoms and causing other electrons to be released. These new electrons also collide with

other atoms, creating a chain reaction that results in thousands of electrons. The final stage of the

image intensifier involves electrons hitting a phosphor screen. The energy of the electrons makes

the phosphor glow. The visual light shows the desired view to the user or to an attached

photographic camera or video device. A green phosphor is used in these applications.

4. Night Vision Device

Night-vision equipment can be split into three broad categories

4.1. Scopes

Normally handheld or mounted on a weapon, scopes are monocular (one eye-piece). Since

scopes are handheld, not worn like goggles, they are good for when you want to get a better look

at a specific object and then return to normal viewing conditions.

Fig5:- scope (monocular)

Depending on the model you can obtain higher power lens sets to economically increase the

observation range of your scope while others can be upgraded with camera adapters to permit

capture of night vision photographs and video. Some scopes can be converted to hands-free

mono-goggles or adapted to weapon mounts to serve as night vision rifle scopes, while others are

best suited to marine applications thanks to their waterproof construction.

4.2. Goggles

While goggles can be handheld, they are most often worn on the head. Goggles are binocular (two eye-pieces) and may have a single lens or stereo lens, depending on the model. Goggles are excellent for constant viewing, such as moving around in a dark building.

Fig6:-goggles worn on the head

Many can be converted to long-range scopes and binoculars and some are even weapon

mountable. While all include integrated short-range infrared illuminators that permit map reading

and room-to-room searches in complete darkness, long-range illumination requires the addition

of one of our infrared sports lights.

4.3. Cameras

Cameras with night-vision technology can send the image to a monitor for display or to a VCR

for recording. When night-vision capability is desired in a permanent location, such as on a

building or as part of the equipment in a helicopter, cameras are used. Many of the newer

camcorders have night vision built right in.

5. Generations

These are the generations of night vision technology

5.1. Generations 0

The earliest (1950) night vision products were based on image conversion, rather than

intensification. They required a source of invisible infrared light mounted on or near the device

to illuminate the target area.

5.2. Generations 1

In generation 1 three image intensifier tubes connected in series. These system are larger and

havier than gen2 and gen3. The gen1 clear at the center but may be distorted around the edges.

Figure illustrate that first generation night vision. Incoming light is collimated by fiber optics

plates before impacting the a photocathode which release electron, which is turn impact a

phosphor screen. The excited screen emits green light in to a second fiber plate, and the process

is repeated. The complete process is repeated three times providing an overall gain of 10,000.

Fig7:-Generations1

5.3. Generations 2

The micro channel plate (MCP) electron multiplier prompted Gen 2development in the 1970s.

The "gain" provided by the MCP eliminated the need forback-to-back tubes - thereby improving

size and image quality. The MCP enableddevelopment of hand held and helmet mounted

goggles.Second-generation image intensification significantly increased gain and resolution

byemploying a microchannel plate.

Figure depicts the basic configuration. These two sentences could have been combined:

"Figure2 depicts how second-generation image ... plate." The microchannel plate is composed of

several million microscopic hollow glass channels fused into a disk. Each channel,

approximately 0.0125 mm in diameter, is coated with a special semiconductor which easily

liberates electrons. A single electron entering a channel initiates an avalanche process of

secondary emission, under influence of an applied voltage, freeing hundreds of electrons. These

electrons, effectively collimated by the channel, increase the resolution of the device.With

additional electron optics, details as fine as 0.025 mm can be realized.Current image intensifiers

incorporate their predecessor's resolution with additional light amplification. The multialkali

photocathode is replaced with a gallium arsenide photocathode; this extends the wavelength

sensitivity of the detector into the nearinfrared. The moon and stars provide light in these

wavelengths, which boosts theeffectively available light by approximately 30%, bringing the

total gain of the systemto around 30,000.

Fig8:-Generations2

5.4. Generation 3

Two major advancements characterized development of Gen 3 in thelate 1970s and early 1980s:

the gallium arsenide photocathode and the ionbarrier 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),

asdemonstrated by actual testing and not extrapolation.

5.5.Generation 4

Generation 4 is used to describe the most advanced night vision technology.  Referred to as

'Filmless & Gated' image intensifiers by the US Military, Generation 4 image tubes provide a

notable improvement over Gen 3 night vision.  They not only offer increased detection range in

pitch-black conditions, but with a dramatically reduced 'halo' they also responsed better to bright

sources.  Whether you are looking for a night vision scope, a hands-free Generation 4 night vison

goggles system, or a night vision weapons sight, we can offer a good selection to choose from. 

We also have Generation 4 night vision binoculars.

Percentage of improving from generation to generation

6. Applications

These are the common applications of night vision technology

1. Military

2. Hunting

3. Security

4. Navigation

5. Wildlife observations

6. Hidden object detection

The original purpose of night vision was to locate enemy target at night. It is extensively by the

military for that purpose, as well as for navigation and targeting. Police and security often use

both thermal imaging and image enhancement technology, particularly for surveillance. Hunter

are use this to detect the animals and any other birds. Detectives and private investigator use

night vision to watch assigned to track.

Many business have permanently-mounted cameras equipped with night vision to monitor

surroundings. A real amazing ability of thermal imaging, is that it reveals whether an has been

distributed , it can show that the ground has been dug up to bury something, even if there is no

obvious sing to the naked eye. Law enforcement has used this to discover items that has been

hidden by the criminal, including money, drugs and bodies. Also recent changes to area such as

walls can be seen using thermal imaging, which have provided important clues in several cases.

Many people are beginning to discover the unique world that can be found after darkness falls.

7. Conclusions

Through night vision device we can see the object in dark environment.We have seen four

generation of this devices and seen different ranges.Initially this device was used by military but

now it also available for civilians.Today in the 21st century we have come a long way in the

development of night vision technology, from the early 1940’s. Night vision devices are

basically designed for utmost defensive purposesbut the application within the scientific or the

civilian range is often prohibited by law.In present scenario the applications of night vision

technology is very essential to combat terrorism which is a major problem being faced by

mankind.

Finally we have seen that use of night vision devices. we find that night vision device is used in

the presence of ambient light or in case of cloudy whether. There are many types of night vision

devices available in the market but in all these devices one things is common: they produced

green light. so in overcast and cloudy whether the performance of night vision devices decreased

means the detection range is decreased compared to ambient light such as moonlight or starlight.

8. References

http://www.photonis.com/nightvision/products/supergen/supergen_specifica

http://www.irinfo.org/articles/03_01_2007_grossman.html

Www.Wikipedia.Org

En.Wikipedia.Org/Wiki/Night_vision_device

Www.Morovision.Com/How_thermal_imaging_works.Htm

En.Wikipedia.Org/Wiki/Night_vision