How Night Vision Works

Night vision technology has been used for decades in military operations, and more recently in law enforcement and wildlife observation operations. This article describes the basics of how night vision works.

Infrared Light

Light is a form of electromagnetic radiation. Visible light is only a small part of the electromagnetic spectrum. The electromagnetic spectrum describes the various wavelengths of electromagnetic radiation, from gamma rays (the highest energy) to radio waves (the lowest energy). The wavelength of visible light is between 0.39 and 0.71 micrometers.

Of all the wavelengths in the spectrum, only a small portion is visible to humans. This portion is called visible light. The rest is invisible to humans, but not to all animals. Some animals are sensitive to infrared light, while others are sensitive to ultraviolet light.

Many insects can see into the ultraviolet portion of the spectrum, which is useful for finding nectar sources in flowers. Some insects are also sensitive to infrared light; this allows them to see in the dark better than humans by detecting differences in temperature that are invisible in the visible portion of the spectrum.

Infrared light has wavelengths longer than visible light. It is sometimes referred to as near-infrared, but it is still infrared in the sense that it is outside the visible light portion of the spectrum. It can be seen by some animals and humans with night vision equipment.

Thermal Imaging

A thermal imaging camera records the thermal radiation emitted by objects in its field of view. In contrast, an optical camera records images based on reflected visible light.

A thermal camera can detect objects that do not reflect visible light well, such as people hiding in shadows or under trees or bushes at night or even during the day if they are wearing dark clothes. It can also detect objects that do not emit visible light at all, such as animals at night and certain types of chemical leaks from tanks and pipes that do not have any flames around them but still give off heat.

Types of Thermal Imaging Devices

Un-cooled –

An un-cooled thermal imaging device is one that does not need a cooling system of any kind in order to operate at its full sensitivity. The disadvantage of this type of system is that it has a low resolution because it uses a small sensor array with low pixel count, so it cannot see fine details very well.

It also has a narrow field of view (about 4 degrees wide) and has poor image quality at long ranges because it suffers from temperature gradients that distort the image by making it look blurry and distorted.

Cryogenically cooled –

A cryogenically cooled thermal imaging device uses liquid nitrogen or liquid helium to keep its sensor array at a temperature just above absolute zero (-460 degrees F). It uses a small lens that focuses an image onto a larger sensor array with a higher pixel count than an un-cooled thermal device, so it can see more detail and has a wider field of view (about 18 degrees wide).

It also has better image quality at long ranges because it does not suffer from temperature gradients that distort its images like un-cooled devices do. The disadvantage is that it uses much more power, and its cooling system makes it heavier and larger than an un-cooled system, so it cannot be mounted on smaller vehicles or handheld devices as easily as an un-cooled system can be.

Another disadvantage is that because it uses liquid helium or nitrogen, it takes longer to cool down when first turned on than an un-cooled system does, which means that it takes longer to begin seeing images after it first turns on than an un-cooled system does.

Image Enhancement

Image enhancement is a process used to improve the quality of thermal images. It can be used to improve the resolution, eliminate thermal noise, or reduce the effects of temperature gradients, which are distortions in the image caused by different temperatures on the sensor array from one part of the image to another.

Generations

Generation 1 –

The earliest thermal imaging devices had no image enhancement capabilities and produced very low-resolution images, even with a cryogenically cooled sensor array. They could see people at a distance of about 600 meters at night and about 100 meters during the day.

Generation 2 –

Generation 2 thermal imaging devices have some image enhancement capabilities and produce slightly better-quality images than generation 1 devices, but they still have low resolution and a narrow field of view. They can see people at a distance of about 650 meters at night and about 150 meters during the day.

Generation 3 –

Generation 3 thermal imaging devices have advanced image enhancement capabilities and produce higher-resolution images than generation 1 or 2 devices. They can see people at a distance of about 700 meters at night and about 200 meters during the day.

(Note: Some generation 3 devices are mechanically cooled instead of cryogenically cooled. These are sometimes called generation 2.5 devices.)

Generation 4 –

Generation 4 thermal imaging devices have the highest level of image enhancement and produce the highest-resolution images available on the market today. They can see people at a distance of about 800 meters at night and about 250 meters during the day.

(Note: The distances given in this article are approximate and are based on an average human body temperature of 93 degrees Fahrenheit. The distances will vary from person to person depending on their body temperature.)

Night Vision Equipment

Night vision equipment (Scopes, Monocular, Goggles, Cameras) is used for surveillance, navigation, target acquisition, and hunting at night or in low-light conditions. Different types of equipment are used for different applications.

Applications for night vision equipment:

Surveillance –

Surveillance is used when a person needs to watch a place, area, or group of people without being seen. In law enforcement, it is usually used to observe suspects without being noticed. In wildlife observation, it is usually used to watch animals without disturbing them or being noticed by them. In military operations, it is used to observe enemy forces without being detected by them.

Navigation –

Navigation is used when a person needs to travel in a place or area without getting lost or running into anything while walking, driving, or flying an aircraft or other vehicle.

Target acquisition –

Target acquisition is used when a person needs to identify a target such as someone or something that needs to be attacked or destroyed, such as an enemy vehicle or tank during wartime or a wild animal that needs to be hunted for food.

Hunting –

Hunting is used when a person needs to find animals for food or sport. It can also be used when someone needs to find sick animals that are infected with diseases such as foot-and-mouth disease so that they can be tracked down and killed before they spread the disease further.

Conclusion

Night vision technology has been around for decades and has been used extensively in military operations around the world ever since it was first developed. It is also used in law enforcement and wildlife observation for surveillance, navigation, target acquisition, and hunting purposes.

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