How Does Night Vision Work?

Due to the growing interest in Night Vision, and the confusion at the performance of what's available, I thought I would delve into this subject. Like many ground breaking technological developments, the origins of Night Vision can be traced back to Germany. One of Hitler's 'super weapons', work on night vision devices was initially undertaken by “Heereswaffenamt” WaPruf 8 and the AEG in 1936. Work on this project was shortlived though, and they did not make any real progress until 1943.

During this same year American engineers tackled the problem of developing a working night vision device. The Americans wanted a weapon’s sight for use on the M1 carbine. The result of their work was the Sniperscope T-120 developed in late 1943. This consisted of an Infrared (IR) spotlight, vertical grip mounted beneath the forearm, and a scope capable of detecting IR light mounted atop the receiver. The scope, spotlight and vertical grip weighed in at 5.7 pounds. However, the complete weight of the system, including the power supply and 6-volt battery, tipped the scales at a portly 21.3 pounds. The way it worked was the IR light mounted on top acted as a big spotlight emitting a beam of IR light invisible to the naked eye. The scope did not amplify light, it was only capable of seeing with the aid of the IR spotlight. Range was only 70 to 100 yards, but it allowed the gunner to “see” in total darkness.

The T-120 was soon followed by improved M1 and M2 models. American units first fielded these early active night vision devices in April of 1945 on Okinawa. Although fewer than 500 units were deployed, they accounted for approximately 30% of all casualties suffered by the Japanese to small arms fire during the first week of this campaign. Despite this early success, incompetence in the US Army prevented night vision equipment from being properly deployed until the war in Vietnam.

Since those first primitive T-120 units went into action NVDs have made great strides forward. No longer simple active IR units dependent on an infrared light source, which anyone with a similar device can see; today's NVDs are passive in nature amplifying available ambient light. As technology has improved the prices on these units has dropped to where 1st Generation units are now widely available at downright cheap prices. This of course raises the questions of, "What does one get for their hard earned money?" and "How much should I spend?"

To better answer these questions Firearms News decided to delve into the darkness. Let’s start by taking a brief look at how this technology works. Modern passive image enhancement night vision operates quite differently from the original active IR units. Rather than relying on an IR light source, modern passive units take the small amount of available light (such as from moonlight or starlight) and converts the light energy (protons) into electrical energy (electrons). These electrons then go through a thin plate containing millions of channels. As the electrons travel through they strike the walls of the channels releasing thousands of more electrons. These multiplied electrons then bounce off of a phosphor screen which converts the electrons back into photons. This provides an image to the ocular allowing you to see in the dark. Simple, right?

Well, the important thing to understand is that all modern passive Night Vision Devices (or Starlight scopes) require some ambient light to amplify in order to see. If you were sealed in a dark room with no light, the best passive Night Vision available would be blind. So the performance of any NVD is directly related to the amount of ambient light available. As examples, viewing a snow covered field on a cloudless night with full moon and stars (optimum), or being in the woods on an overcast night with no moon or stars visible (poor conditions). Also, as Night Vision is very responsive to reflective ambient light, light reflecting off of fog or heavy rain may also seriously degrade performance.

Performance is also directly related to the type of NVD in question. In this regard NVDs are classified by Generations. The higher the generation the more sophisticated the night vision technology.

Generation 0: The earliest units dating from the 1940s and 1950s requiring an outside source of invisible infrared light to illuminate the viewing area. The last US military Gen O device was the AN/PAS-4 developed in 1962 for use on the M14 rifle and fielded until approximately 1970. Today this technology is reserved for equipment such as mounted security cameras.

Generation 1: This technology dates from the 1960s. Military units from this period are very large and heavy, common examples being the US Army's AN/PVS-2 and Soviet 1PN-58. Currently there is a bewildering array of inexpensive commercial 1st Generation NVDs available. Performance of these cheap units is usually poor. Switching the unit on provides a dim, pale green image. The image itself is usually rather grainy with noticeable Geometric Distortion at the edges. Under 'perfect' conditions (cloudless sky with full moon and stars present) these units are certainly usable. As ambient light decreases, such as stepping into the woods or under cloud cover, performance drops off noticeably. In lowlight conditions these units benefit greatly from an IR illuminator, which basically acts as a flashlight. By teaming a high quality IR illuminator with a Gen 1 device, short range performance can be made acceptable. The end result of using a Gen 1 device teamed with an IR illuminator is basically the same as a Gen 0 device.

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Generation 2: This technology dates from the 1970s and is a noticeable step up from the Gen 1 units. Military weapon sights from this period, such as the American AN/PVS-4 and Soviet 1PN-51, though smaller, are still rather large and heavy. The US AN/PVS-5 goggles though are a practical size. Commercial Gen 2 NVDs are noticeably more expensive than the Gen 1 units. However, they do offer a notable increase in performance. The image is usually flat with good resolution from its center almost to the edges. Gone is the Geometric Distortion of the Gen 1 units, and the image is noticeably brighter. Depending upon the model, tube quality and overall quality of manufacture a Gen 2 device can offer quite acceptable performance at a price many can live with. Performance though is still a step down from a high quality Gen 3 device.

Generation 3: Dating from the 1990s, a brighter sharper image was gained by adding gallium arsenide to the photocathode. An ion barrier film also increased tube life dramatically. Military units, such as the AN/PVS-14 are surprisingly small and lightweight. Performance is impressive. With a Gen 1 device, in poor lighting you strain so hard to discern something out of the snowy murk that you'll just about pop a retina. With a Gen 3 unit night suddenly gives way to day. The image is very flat and clean from edge to edge. Resolution is very good and depth perception fairly good as well. The difference between a Mil Spec Gen 2 and Gen 3 unit is fairly substantial.

NVDs also come in a wide array of formats. These include monoculars, binoculars, goggles and weapon sights. When choosing a device, carefully consider exactly what you will be using it for and how you intend on using it. If you'll be predominantly scanning from a static position, then a binocular may be your best bet. If you're traveling through the woods though, you may want to consider a goggle or head mountable monocular. Also be sure to take into account size, weight, battery type, and control placement when choosing a device. Remember, ease of operation, such as changing batteries, must be measured in total darkness where you cannot see the device being used. If you plan on using it in the field the ability to operate under adverse environmental conditions is vitally important.

For increased versatility I recommend a monocular that can be hand held, deployed hands free via a head mount, or mounted to a weapon. While a viewing monocular lacks a reticle for aiming, they can be mounted behind a Red Dot sight (with Night Vision settings such as an Aimpoint or EOTech), used in conjunction with an IR laser, or mounted to the ocular of a rifle scope with an illuminated reticle. This makes for a very flexible tool capable of accomplishing a wide variety of tasks. Please keep in mind though that if you mount a monocular behind a daylight optic, performance is severely degraded.

Properly used, a high quality NVD can be a great aid in a variety of lowlight scenarios. However, it is not a miracle technology. Night vision does have limitations and weaknesses. To make the most of it requires proper training. If you're interested in purchasing night vision I strongly suggest doing extensive research on-line before laying down your hard earned cash. Take the time to educate yourself to understand which generation device will best meet your needs. Then research different devices and companies to buy from. The last piece of advice I will leave you with is, if it sounds too good to be true, it probably is.