How Does Night Vision Work?

Night vision is a biological adaptation that occurs in nature, predominantly in nocturnal animals or those that reside in dark environments. Although humans have not biologically adapted this trait, they have found a way to obtain the benefits of night vision through technology. But without light, how does night vision in technology work?

Older night vision technology uses optoelectronic image enhancement. The device lens senses infrared light reflected off of objects, which is electrically amplified and sent to a display screen. Modern night vision technology uses digital image enhancement, which captures light on a digital image sensor, and then the digitally enhanced image is displayed. 

Read on to learn more about how night vision works in both older and newer generations of these devices. We’ll also discuss how the generations have progressed, and the technology has changed over the years, as well as where night vision technology is headed in the future.

How Optoelectronic Image Enhancement Works In Night Vision Devices?

There are two ways that night vision can work. Devices will either utilize optoelectronic image enhancement or use a modernized version of this known as digital image enhancement. Optoelectronic image enhancement was the first technological design used for night vision devices, and so, it is typically seen in older devices dating back to night vision’s origins in 1929. 

In the simplest terms, this technology needs three key components to work:

• Light sources (infrared and some degree of natural or unnatural light)
• Lenses
• A tube 

Essentially, the night vision device will sense small amounts of infrared light when reflected off objects and then electrically amplify and convert that light, so it is visually apparent to the user. Now, of course, it isn’t actually that simple. There is much more technologically and scientifically that goes into how night vision devices using optoelectronic image enhancement really work. To start, these types of night vision devices are comprised of multiple lenses that are supported with a special electronic vacuum tube. Together, these components capture and amplify both visible and infrared light as it is reflected off of nearby objects. Of these multiple lenses, the first found within the system is the objective lens, which is responsible for capturing dim visible light, either natural or unnatural, as it is reflected off an object. In addition to this light source, it will also reflect a small degree of light from the low end of the infrared spectrum. The most crucial element of both these light sources is the photons they are comprised of. These small particles will pass through the objective lens and into the next device component, the image-intensifier tube.

As another key component of night vision devices, the image-intensified tube is a special electronic vacuum tube powered by small AA or N-cell batteries. There are two components to this tube, the photocathode and the microchannel plate (MCP). First, the photons from both light sources will pass through the photocathode, where they are converted into electrons. Once these electrons are created, they then travel to the MCP, a small disc that is pocketed with millions of minuscule holes. As the electrons pass through this disc, they are exponentially multiplied, amplifying the electric signal as bursts of voltage cause the motion to increase substantially. After this process is complete, the electrons will exit the image-intensifier tube and strike the final component, a phosphor-coated screen. This substance is used strictly for its luminance effect, which appears bright green when the dense cloud of electrons hits the screen. A glowing image is then created, which can be viewed through an ocular lens on the device.

How Digital Image Enhancement Works In Night Vision Devices

Digital image enhancement is used in much more modern night vision technology but still derives a great deal of its technological design from optoelectronic image enhancement. Many of the components of night vision devices are the same here. For instance, the process still begins with infrared and natural or unnatural light hitting the objective lens. However, rather than going into an image-intensified tube for conversion, the light is converted into a digital signal using a complementary metal-oxide-semiconductor (CMOS) sensor. Afterward, the digital signal is then electronically enhanced and amplified enough to be sent to the LCD screen, where it is visible to the user. 

This technology allows for more high-definition visuals from the night vision devices and allows them to be smaller and lighter than those created with optoelectronic image enhancement. The increased versatility is exceptionally beneficial since night vision devices are typically used by hunters or military personnel, both of which must efficiently manage the weight they carry. Another benefit of the rise of digital technology is that these night vision devices are compatible with other technologies for easy connection. Their footage can also be stored on SD cards and USB drives and can be sent to smartphones, computers, and other digital devices.  

How Night Vision Has Developed Over Time

Despite its exceptional benefits to technologies such as cameras, binoculars, and weaponry, night vision development isn’t even a century old yet. However, its technology has changed significantly from its inception up to the modern era. This progression is important to discuss to comprehensively understand how night vision devices work and what their future may hold.

Origins of Night Vision: Gen-0

The history of night vision technology is heavily rooted in the enhancement of military weaponry, particularly in gun sights, binoculars, and telescopic rangefinders. Less than a century ago, in 1929, a Hungarian physicist named Kalman Tihanyi discovered that it was possible to create infrared-sensitive lights. He then invented the infrared-sensitive electronic television camera for anti-aircraft defense in the UK. This revolutionary breakthrough was then adapted to create the first night vision device in 1930 by a German producer of electrical equipment known as Allgemeine Elektricitäts-Gesellschaft (AEG).   

The purpose of these technologies was to give German soldiers and military forces an edge in the field during World War II. However, it was long until the United States caught wind of the invention and was hot on Germany’s heals, utilizing and enhancing it to their benefit. These early night vision devices, referred to as “generation zero or Gen-0” technologies, were active devices that worked with the assistance of a large infrared light source, or infrared (IR) illuminator, to amplify existing light about 1,000 times. They were also the first examples of optoelectronic image enhancement, although they lacked certain components that would be added in later generations for improved functionality.

The IR illuminator was either attached to the night vision device or something nearby and would shoot a beam of infrared light invisible to the naked eye. The beam of light then reflects off of objects within the vicinity, and the existing light is then amplified before it is sent it back to the night vision device. Within the night vision device are intensifier tubes consistent with early optoelectronic image enhancement technology that converted this infrared light by using an ‘anode’ and a ‘cathode’ to accelerate the electrons. One significant issue with the active design was that the electrons’ acceleration often distorted the image, inhibiting the odds of accuracy while simultaneously decreasing tube life. Other issues were that once enemy forces duplicated this technology, they could see the infrared light using their own night vision devices if they were in the vicinity. 

The devices and IR illuminators were also exceedingly cumbersome and bulky. As a result, they were typically fixated onto Panther tanks, or smaller versions were attached to Sturmgewehr 44 assault rifles. Consequently, they assisted in improving nighttime vision, but they were also exceptionally large and obvious targets for enemy forces. The years 1929 to 1939 were monumental to the development of night vision technology as nations worldwide competed to create the best goggles, binoculars, and other military support devices to win the war. However, the technology had a long way to go before it was realistically beneficial in the field.

Origins of Night Vision: Gen-1

When the 1960s rolled around and the United States battled in Vietnam, the use of night vision devices increased substantially as the US Army increased efforts to improve this technology. This is the era of Generation 1 night vision devices, which were the first passive devices created and had a multitude of improvements and enhancements over the Gen 0 technology. Arguably the most influential and substantial alteration found in Gen 1 devices was that they no longer relied on the bulky IR illuminators to have sufficient infrared light to function. Instead, the devices were modified to use ambient infrared light provided at night by the moon and the stars. 

Not only was this alteration more convenient to the device’s design in terms of size, weight, and necessary accessories, but it also substantially enhanced any infrared light reflected within the environment. However, as is consistent with progression, there was a profound drawback to this design. Because the new night vision devices relied heavily on light from the moon and stars to function, they were essentially useless on cloudy or moonless nights when deprived of their essential light. It is also important to note that in terms of internal design, Gen-1 was nearly identical to Gen-0 devices when it came to the image-intensifier tube technology, and so, the drawbacks previously discussed from this design still remained as well.

Origins of Night Vision: Gen-2

Gen-2 night vision devices were created in the 1970s, only about a decade after the modified Gen-1 was released. This generation is important because it finally eradicated one of the more problematic issues of the previous two generations regarding limited vision in low-light environments. Firstly, Gen-2 devices are where you finally see the microchannel plate’s addition in the image intensifier tube. Supported with an S-25 photocathode, the microchannel plate is the component essential to multiplying and amplifying the electrons much more significantly than in previous models.

As a result, Gen-2 devices had increased sensitivity which helped images appear much clearer and brighter to the viewer, particularly around the lens, for improved night time vision. At this point, light amplification has improved from 1,000 in Gen-0 to around 20,000. Therefore, this component removed the previous obstacle of using night vision devices without the moon or stars’ assistance because it allowed functionality in low-light conditions for improved vision and reliability.

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ATN NVG7-2 Night Vision Goggles (Source) & View quality (Source)

Origins of Night Vision: Gen 3

Nearly two decades later, in the mid-1980s, Gen-3 technology was released. Despite having few alterations from the Gen-2, Gen-3 devices had higher resolution and sensitivity and finally solved the prominent issue regarding the longevity of the image-intensified tube. The most significant development of the Gen-3 night vision devices was that the photocathode was composed of gallium arsenide. This compound is exceptional at converting photons to electrons and is why Gen-3 devices have improved resolution and sensitivity. With the Gen-3 devices, amplification reached between 30,000–50,000. Another important distinction is that the microchannel plates in Gen-3 devices were coated with an ion barrier film. This finally helped solve the issue of short-lived image-intensified tubes by drastically increasing their longevity. 

Of course, this addition also had its drawbacks. As a result of the new ion barrier film, far fewer electrons could pass through micro-channel plates. Since these plates were improved with the gallium-arsenide photocathode, expectations were much higher for these devices, but in the end, much of its potential was diminished because of the ion barrier’s effect on other components. In the end, the final image was still higher in resolution, but it also had a distinct “halo” effect around bright spots and light sources that was much larger than normal. The new tubes also required a significant amount of power which increased the device’s overall consumption rate. Ultimately, the Gen-3 followed in the footsteps of previous generations in taking two steps forward in resolution and sensitivity but one step back in overall functionality.

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Origins of Night Vision: Gen 4/Gen 3+

The final and most current generation of night vision technology is what consumers refer to as GEN-4. However, the US Army Night Vision and Electronic Sensors Directorate (NVESD) plays a significant role in the governing body that names the generation of night-vision technologies, and they have not yet authorized the use of the Gen-4 title concerning this model. Instead, they refer to this generation as Gen 3+, and so, you might see the names Gen-4 and Gen 3+ used interchangeably as well as GEN-III OMNI-V–VII, but they are ultimate all the same model. Now that any confusion surrounding the name has been clarified, we can discuss what changed between Gen 3 and Gen 3+ devices. 

Developed in the 2000s, Gen 3+ is a more fine-tuned night vision device where many of the older model’s issues are resolved without risking overall functionality. These are ultimately the most advanced night vision devices and are currently used in the US Military by special operators (S.O.) and other forces. This is partially due to the exceptional design allowing the devices to function well in both low- and high-level light environments. One of the most significant changes found in Gen 3+ devices is that the ion barrier film initially added to Gen 3 devices has been removed. This component caused significant complications with visual distortion in the previous generation, and so it was more beneficial to remove it altogether. With the ion barrier no longer inhibiting electrons’ flow through the micro-channel plates, these devices have a much clearer and brighter image, free of excess distortion. The removal of this component also reduced background and helped enhance the signal-to-noise ratio.

The removal of the ion barrier does pose a concern to the longevity of the tubes. Fortunately, this is more or less “negated by the low number of image intensifier tubes that reach 15000 h of operation before replacement.” The second most significant change to the Gen 3+ devices is the addition of an automatic gated power supply system or autogated tubes. This component permits the regulation of the photocathode voltage by rapidly turning it on and off as necessary. This allows night vision devices to adapt to various light conditions efficiently and instantaneously. Now, users are no longer inhibited by the device when switching rapidly from a low-light to high-light environment or vice versa. It is also important to note that these autogating power supplies are compatible with previous generations and can be added to these devices for more efficient lighting transitions.  

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Can Night Vision Work in Total Darkness?

After discussing the various ways that night vision technology can work, it is clear that they are used in dark environments. However, one word that seems to frequently appear when describing how they work is “light.” However, there are several locations where a night vision user could go that are ultimately devoid of light and bathed in total darkness. Which begs the question of whether their high-tech, Gen 3+ night vision goggles will work here. Unfortunately, the answer is currently no. Regardless of how advanced night vision technology is, it still relies on a source of natural ambient infrared light. 

This light is typically obtained from the moon or the stars to some degree rather than a separate infrared light, as seen with Gen-0. But since all night vision devices are built around utilizing some passive form of infrared light, they cannot function in an environment of total darkness. Typically, if someone is searching for technology that allows them to see to some degree in total darkness, they will turn towards thermal technology overnight vision. 

Why Does Night Vision Appear Green?

The telltale sign of a night vision video is its signature green glow. But what many don’t understand is why nearly all night vision devices have this color versus one or several others. First, it was essential to the design of night vision technology that at least one color was assigned to be displayed on screens. Since these devices are ultimately powered through photon-converted electrons, no color information is carried to the night vision device as it is stripped during the conversion process. Therefore, a color needed to be chosen as the images would originally appear in black and white, which is far more difficult to view. 

Green was the answer because it is the easiest color to view for extended periods in the dark. Another reason is that according to AGM, “the human eye is most sensitive to the green color pallet and distinguishes more shades of green than any other color.” Now, as to where this color comes from, the answer lies in the phosphor-coated screen. We’ve discussed where this screen appears in the overall process of how night vision devices work. Essentially, after the electrons are amplified and multiply from passing through the microchannel plate, they strike the phosphor-coated screen with such intensity that it results in the bright glowing green we know today. 

Can Night Vision Work in Full Color?

Color night vision isn’t really seen proficiently in modern night vision technology yet because of the significant obstacles that must be overcome to achieve this. The most prominent obstacle is that the conversion process necessary for night vision devices completely strips all pre-existing color information. Therefore, the device doesn’t really know the color of the objects it is viewing because this information has been removed before it reaches the screen. Currently, night vision technology is not sensitive enough in low-light conditions to accurately capture enough light during the process in order to amplify the results into a color picture.

For this reason, any form of color night vision technology isn’t truly effective without a substantial degree of ambient light. It is more likely to be functional in domestic settings, such as the exterior of a home with the support of a porch light, rather than in the military field where users rely on light from the moon and stars. However, there has been substantial research and development in the field of color night vision over the past few decades, and some significant headway has been made. 

There are some lower-end forms of this technology that rely on adding filters to traditional image intensification systems, but there are several high-quality color night vision devices that are sold on the commercial market and used in the military today. As we mentioned previously, the biggest drawback is that these filterless color night vision devices need ambient light to function, and so, they aren’t as versatile as the standard models. One a handful are advanced enough to function off of moonlight alone, and even fewer can function with ambient light from the stars.

The Future of Night Vision Devices

Modern-day night vision devices can amplify light by 50,000 times or more, an almost inconceivable amount compared to the amplification power of 1000 seen in Gen-0. Scientists today strive to “conquest the darkness,'” in the words of Dr. James Bald, through innovative advancements that continue to push the limits of night vision technology. We’ve discussed one of the newer developments in color night vision, but there has also been rewarding new discoveries in the realms of:

• Panoramic Night-Vision Goggles (PNVGs)
• Enhanced Night Vision Goggles (ENVG) that combine thermal imaging with image intensification
• Ceramic Optical Ruggedized Engine (CORE), which produces higher-performance Gen 1 tubes
• Night vision contact lenses

These innovations can or have already revolutionized the world of night vision devices. Take night vision contact lenses, for example. This development is being pursued by scientists at the University of Michigan, where they are inserting a thin strip of graphene, pure-carbon mono-layer material, between layers of glass. This graphene layer then reacts to photons in order to make dark images appear brighter. A prototype of this has already been created and currently absorbs 2.3% of light. Although this percentage is still far too low to be viable for use, it would revolutionize the industry, particularly the market, as they would most likely replace night vision goggles. 

Army personnel is particularly interested in the progression of night vision contacts in addition to another innovation that is a little less technological, night vision eye injections. Although testing and research for this advancement are still very new, Xue Tian, a Hefei-based vision physiology expert, and Gang Han, a Worcester-based nanoparticle expert, explore the possibilities of injecting nanoparticles into the eye to provide night vision. The nanoparticles would convert near-infrared light into visible light and would also eradicate the need for cumbersome night vision goggles if successfully developed. 

Final Thoughts

Night vision technology has advanced substantially in the near-century since its inception. Once a tool of warfare used only for soldiers, night vision is now available commercially and can be utilized by anyone from recreational hunters to homeowners protecting their property. There is a significant amount of potential within this technological realm, particularly when scientists can overcome the hurdles posed by the necessity of ambient light for functionality. Perhaps in time, we will see some of the most beloved and staple night vision inventions replaced by more advanced, erring on natural, alternatives.