Photos courtesy Pentagon Light
Photos courtesy Pentagon Light
FEATURED IN TACTICS AND WEAPONS
We've all seen low-light footage on the news, those ghostly, green images from Iraq, Afghanistan and other battlefields. If you didn't know better, you'd think you were looking at a daylight scene through a green filter until you notice that light sources show as large blooms of radiance, and close-ups of Marines show strange glowing eyes. The images are spooky.
What we're seeing is video shot through night-vision gear, sometimes abbreviated to NVD for night-vision device. It's one of the technological breakthroughs that allows our service men and women to function more safely in a battlefield environment. It also can help law enforcement, particularly tactical teams.
How Does It Work?
NVDs were developed near the end of WWII. The earliest units were active devices, meaning they emitted infrared light and then picked up the reflected infrared light with the NVD to illuminate the scene to the wearer. Ultimately, the early 1960s saw the development of passive NVDs, wherein the NVD could amplify ambient light without requiring an active infrared emitter.
Simply put, NVDs use a photocathode tube to convert and intensify light electrons and then display them on a fluorescent screen, where the wearer will see the image in a green tint. (Green is purposely used because the human eye can more readily differentiate between shades of green than other phosphor colors.) Thus, NVDs allow the wearer to see in low-light conditions, and sometimes in total darkness.
There are four generations of NVDs, with each succeeding generation improving on the last.
1st Generation (Gen 1): A photocathode tube transforms photons of available light into electrons, then amplifies them through an electro-chemical process, after which a phosphorous screen converts the amplified electrons back to a visible image much brighter than the original.
2nd Generation (Gen 2): essentially the same as Gen 1, but with an additional plate behind the photocathode, which adds greatly to the brightness amplification.
3rd Generation (Gen 3): adds the chemical gallium arsenide to the photocathode, which makes the image brighter and sharper than in Gen 2.
4th Generation (Gen 4): uses gated-filmless technology, which removes the ion barrier film, resulting in much-improved target detection and resolution, especially in very low light.
Ideally, night vision would be just as clear and sharp as normal daytime vision. Although we're not there yet, the most recent NVDs get us amazingly close.
NVDs are not magic you still must have some ambient light for the photocathode tube to collect and then amplify. Usually this condition is met through the presence of starlight or moonlight. However, sometimes that's just not enough, or perhaps the wearer is inside a building where there is no ambient light. How then to use the NVD? The solution: Use an infrared illuminator (IRI). An IRI puts out a beam of infrared light all but invisible to the naked eye. The NVD picks up the infrared photons similar to its normal operation, and the result is basically the same.
This works well, unless your opponent also has an NVD. In that case, your infrared illuminator will show up like a flashlight beam on a dark night, making you a well-lit target.
Passive NVDs (gear without an image intensifier) hold several advantages over active NVDs: They are lighter, smaller, require less power and cost less. (These attributes have made it possible for the military to provide many personnel with individually worn units.) However, as previously mentioned, without an active infrared source, image intensifiers do not work well in complete darkness.
Looking through an NVD is similar to looking down a tunnel. In effect, there is no peripheral vision. Normal human field of vision covers roughly 190 degrees, but NVDs reduce that to about 40 degrees. This requires the wearer to constantly scan for threats.
Even under optimal viewing conditions with adequate illumination and high contrast between the target and the background, NVDs still cannot equal the clarity of normal human vision. The human eye is capable of 20/20 vision, but NVDs can deliver, at best, 20/25 20/40. As the scene's contrast diminishes or as the ambient light decreases, the image seen through the device will grow increasingly fuzzy.
An NVD can affect depth perception as well. While normal human perception relies upon binocular vision for depth perception, when you look through an NVD, you are, in essence, using one eye (monocular vision). In one common perceptual distortion, when you look at two objects of different sizes side by side, the larger one will appear closer. Another common effect: Some objects will appear to be farther away than they are because our mind thinks fuzzier images are farther away. Recently introduced dual-tube systems begin to address this depth-perception problem by giving the wearer binocular vision.
One common misconception: If you shine a bright light into an NVD, the wearer will be blinded (a scene involving this is written into just about every movie script involving the use of an NVD). Not true. These devices have protection circuits built in that will shut down the mechanism within a second or less should the incoming light get too intense. Once this occurs, it can take two minutes or more for the device to reset itself.
The Market Shifts
In the beginning, research and development in the night-vision field was driven by the military. From the first, pre-Gen 1 units of the 1940s and 1950s, through the Starlight Scopes of Gen 1 and into the 1990s' development of Gen 3 devices, the military's need for smaller, more efficient, less power-hungry and more reliable NVDs drove the industry.
As the military cut back on its research efforts, the NVD industry began to expand into consumer markets, searching for more outlets for its products. As a result, while night-vision gear still tends to cost a lot, especially the Gen 2 variety, more and more units are becoming available to the civilian sporting and recreation market.
This market shift has given rise to greater availability and lower prices. Law enforcement agencies, and in some cases, individual officers, are taking increasing advantage of this market shift. Gen 1 monocular units can be had for as little as $100.
Why Would You Need One?
Tactical uses for NVDs are readily apparent, but why would the average patrol officer want one? After all, many of us worked for years without the ability to see in the dark, carrots for dinner notwithstanding.
I can remember many times when I was checking a building with my partner, standing in the shadows, staring intently into dark corners of a warehouse or other location, trying to figure out if I was seeing a bad guy or a pile of boxes. We know the human eye strains to see detail in low-light conditions, especially with the central vision we use when we stare directly at something, and a handheld monocular type NVD sure would come in handy during those times when we just aren't sure and don't want to use our flashlight.
What Do You Need?
If you're shopping for NVDs for your tactical team or some other specialized unit, you'll obviously have more money to spend and significant, mission-critical, needs. In that case, buy the best you can afford. Usually this means later-generation units because they possess greater capabilities. Typically, you'll want Gen 2 units.
On the other hand, if you're shopping for an NVD for patrol or personal use, your budget will likely remain small, and you'll gravitate toward Gen 1 units. Keep in mind that although Gen 1 units cost less than later generations, they are still viable tools.
Most Gen 1 units available in the United States are actually manufactured in Russia, which has a reputation for pretty high-quality devices. Gen 2 and Gen 3 units are largely manufactured in the United States. They usually cost a lot more due to their enhanced capabilities.
Higher magnification units are not necessarily better. An NVD used as a rifle scope, for example, might offer relatively high magnification, but if the resolution and image gain are inadequate, the image will appear dark and muddy. Look for a unit that balances three attributes: magnification, resolution and image gain.
By the way, you must consider two other concerns. First, most NVDs are water resistant, but not waterproof. Unless it's specifically designated as waterproof, don't expose your device to water or even long periods of high humidity.
Second, these are powered devices. Some will run on battery power for as long as 20 30 hours with the infrared illuminator turned off, but if you intend to use your IRI for extended periods of time, cut that figure in half. On the plus side, most units are powered by readily available AA, 9V or 3V lithium batteries. Carry spare batteries.
Stay safe, and wear your vest.
Falling prices mean the bad guys can more easily obtain NVDs, too. If you find one on a suspect, take a moment to think about what that means. What criminal activity would it allow them to engage in? ed.
Night-Vision Resources Online
www.nightvision.com ITT, one of the major night-vision gear manufacturers, offers much information on how gear works, plus law enforcement applications. Check out the video on the How it Works page.
www.nightvisionbinoculars.com/buytiphowtom.html This commercial site offers a good explanation of how NVDs work.
www.theppsc.org For an excellent discussion of how the eye performs in low-light (related to shooting skills), click on Staff Views near the center of the home page, click on Staff Views on the left of the next page, then scroll down and click on the article by Paul Michel titled "Visual Perception in Low-Light Levels." To see a three-part series on police training in low light, register for a free password, then click on Archives on the home page.
http://health.howstuffworks.com/eye1.htm A fascinating series of pages by a doctor on how the eye works.