Night Vision “We Own the Night”
Night Optical Devices (NODs) give US forces a significant advantage when operating under conditions of little or no light. There is such a thing as “no light,” and there are devices that allow us to see under conditions of “no light.” Some of this discussion is a little technical, but we’ll make it as painless as possible.
A lot of material in the public domain talks about a bewildering selection of equipment without explaining what is going on under the hood. This piece is meant to fill that gap.
The Electromagnetic Spectrum
We need to understand a little physics and a little biology. In the first case, we need to understand what we mean by “light,” and in the second case, we need to understand how our eyes are constructed to convey light information to the brain.
First, the physics. Objects reflect electromagnetic radiation. Physicists speak of “light” as electromagnetic radiation that comes in “particles” and “waves.” How can light be both a particle and a wave? Don’t worry; just accept the physics for now. What you need to know is that the waves come in a range – or spectrum – of wavelengths, measured in micrometers or microns.
Visible light comes from the range of the spectrum between 0.4 and 0.7 microns. Those are colors we can see, all the way from violet at the low end of 0.4 to red at the high end of 0.7. “Near-infrared (IR)” light is not visible to our naked eyes. Near-IR light extends from 0.7 to 1.3 microns. Mid-IR light extends from 1.3 to 3 microns, and Thermal IR extends from 3 to 30 microns. Here, we’ll talk about light in the visible spectrum and Near-IR spectrum – from 0.4 to 1.3 microns. We’ll explain why those numbers are important. Figure 1 illustrates the visible and Near-IR electromagnetic spectrum.
The Types of Night Vision
- Direct Illumination
We see objects when light waves reflect from them and are processed by our eyes. Objects absorb certain wavelengths and reflect others. When we see a red dress, the material of that dress absorbs all the wavelengths except 0.7 microns (red) and reflects red to our eyes.
Our eyes only process light in the visible spectrum of 0.3 to 0.7 microns. Above that, we can’t see. If it’s pitch dark and we shine a light with a wavelength of 0.8 microns on a truck (remember that Near-IR is 0.7 to 1.3 microns), we can’t see that light, and we can’t see the truck with our naked eye. No one in the area will be able to see it. It’s invisible. But the truck will reflect those 0.8-micron waves. If we have a scope that collects those 0.8-micron waves and shifts them down into the higher end of the visible spectrum that we can see, we have night vision.
- Ambient Light Intensification
The problem with direct illumination is… zero IR light discipline. Anyone in the area with an IR scope will spot that lamp and kill our sniper. To be truly effective, we need night vision that doesn’t require illumination.
From the 1960s to the present day, night optical devices have been developed to intensify the ambient light that falls on a scene. In simple terms, image intensification devices amplify those small amounts of light until the image is visible to our eye.
These devices progressed through three generations of development, which we will cover in the next section.
- Thermal Imaging
The third night vision technology is thermal imaging. It is a different technology than direct illumination and image intensification, so we will treat it in a separate article. As a teaser, ask yourself: “Can you use NODs in a sealed, windowless room, with no light?”
The answer is “You cannot use Ambient Light Intensification technology (Generation One to Three) because there is no ambient light for the device to amplify. You must either use direct illumination or thermal imaging. And that is all we will say on the subject in this article.
Evolution of Night Vision
Generation Zero (Direct Illumination)
In World War II, snipers on both sides mounted lamps on their rifles that projected Near-IR light of 0.8 to 1.0 microns over a broad area. They also mounted a nightscope on their rifle that could detect the 0.8-micron waves reflected from the target and translate them to a visible image. Figure 2 shows an M-1 Garand sniper rifle, equipped with an IR illuminator and IR sniper scope.
Science fiction fans were introduced to this technology by Charlton Heston in “The Omega Man.” Figure 3 shows our hero on the balcony of his penthouse, taking out baddies with a BAR equipped with IR illuminator and sniper scope.
That was a movie setup. In practice, the illuminator would appear very dark red, verging on black. Why? The lamp projects the full spectrum of radiation, and the glass is a filter that screens out all but the 0.8 or 0.9-micron wavelength. Since that light is not visible to the naked eye, the lamp would look black.
Generation One (Vietnam-era)
During the Vietnam war, the military introduced technology that did away with the need for direct illumination. They developed the ability to electronically amplify ambient light from the moon and stars. These devices were called “starlight scopes.”
Figure 4 shows a Generation One starlight scope mounted on an M-14. Notice that it does away with the IR illuminator.
The scope itself was bulky. It consisted of three light amplification modules stacked inside the tube. There were two problems that remained. The first was bulk, the second was low sensitivity.
Generation Two (The Seventies and Eighties)
The starlight scope was improved with internal components that we will not discuss here. Intensification was increased so that Generation Two scopes were effective on cloudy nights. Increased intensification did away with the need to stack amplifiers and rendered the Generation Two scopes more compact.
Generation Three (Nineties to present day)
This technology introduced gallium arsenide to enhance the conversion of photons to electrons. (Remember we said earlier that light behaved as both particles and waves? Photons are particles of light. Light can be both waves and particles at the same time. Generation Three technology improves night vision by improving the way the device handles light particles.)
Figure 5 shows an AN/PVS-31, the military specification of which is favored by many operators. It is available in both green and blue-white phosphor, which refers to the color cast of the image.
Beyond Generation Three
- White Phosphor
While there is no formal generation beyond Generation Three, improvements are constantly introduced. Early images were the green tone familiar to all. This was due to the nature of the phosphors used. Green images frequently lack contrast and resolution.
Remember, we said some understanding of physics and biology would be required. Here’s the biology. The retina of our eyes is like a film on which the lens casts the image our brains process. There are two kinds of cells in our retinas – rods and cones. Cones occupy the center and are best for sharp focus. Rods lie on the edges and are best for low light. Rods do not process green wavelengths well. They process blue wavelengths best. Later Generation Three devices introduced white phosphor technology. White phosphors look bluish and emit light in the sweet spot our rods like to see.
When you see images from NODs, you see many with green palettes, but bluish-white palettes are increasingly common. Operators call these “white-hot” palettes, and they look like black-and-white photographs, with a faint bluish cast. These images are contrastier, and give the impression of higher resolution.
- Panoramic NODs
Binocular NODs lack peripheral vision. Looking through these is “a great view through a pair of drinking straws.” To improve peripheral vision, the GPNVG-18 (Ground Panoramic Night Vision Goggles-18) was introduced. This device sports four tubes arrayed in an arc. It displays the image in an ellipse across the operator’s field of vision. Figure 6 shows a helmet-mounted GPNVG-18.
The quad-tube can be heavy and uncomfortable over long periods. As usual, the choice comes down to personal preference and logistic availability.
- Laser Sights
Movies often show operators entering a room with red lasers stabbing from their weapons. From what we’ve learned, we should understand right away that those beams are red light in the visible spectrum. Bad guys can follow those beams right back to their source and plug ‘em.
In short, that doesn’t happen. Operators use IR lasers to cast IR on their targets. The IR lasers are invisible to the naked eye, but visible to people wearing NODs.
Why?
Let’s review our numbers. The AN/PVS-31 is sensitive to wavelengths up to about 1.0 micron. IR laser designators need to generate IR in the Near-IR spectrum above the 0.7 micron limit of the human eye but below the roughly 1.0 micron limit of the AN/PVS-31. IR laser aiming modules generate beams in the 0.8-0.9 micron range.
The operator zeroes his IR laser just like he zeroes iron or telescopic sights (with some nuance due to where the laser is mounted relative to the bore – we will write another post on zeroing IR lasers). This is usually done in broad daylight with a visible laser “slaved” to the IR laser. Zeroing the visible laser automatically zeroes the IR laser.
Laser aiming modules often come with four components: an IR laser in the 0.8-0.9 micron range, a visible laser in the 0.4-0.7 micron range, an IR illuminator, and a visible light illuminator.
Summary
In summary, there are three kinds of night vision: Direct illumination, image intensification, and thermal imagery. The problem with direct illumination is that it can give away the observer’s position. Image intensification allows us to operate under conditions of near-total darkness so long as there is some light. In cases of total darkness, where there is no light, there is nothing to amplify. In such cases, we must resort to thermal imagery. We will cover thermal imagery in a later post.
About the Author
Cameron Curtis has spent thirty years on trade floors as a trader and risk manager. He was on the trade floor when Saddam’s tanks rolled into Kuwait, when the air wars opened over Baghdad and Belgrade, and when the financial crisis swallowed the world. Having written fiction as a child, he is the author of the Breed action thriller series, available on Amazon.
Check out his new Breed thriller, BLOOD SPORT, here:
https://www.amazon.com/dp/B0D6RC5V4V
And visit the Breed series page, here:
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Disclaimer: SOFREP utilizes AI for image generation and article research. Occasionally, it’s like handing a chimpanzee the keys to your liquor cabinet. It’s not always perfect and if a mistake is made, we own up to it full stop. In a world where information comes at us in tidal waves, it is an important tool that helps us sift through the brass for live rounds.
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