If you are curious about how night vision cameras ‘see’ in near pitch dark situations, below is the science behind it. Read on as I shed some light—pun intended—on this particular topic.
When I think about night vision, the first image that pops into my head is a soldier with a pair of night-vision goggles. Or maybe action or spy movies in which the protagonist usually uses high-tech gadgets to see in low-light situations. Then I often wonder if those pieces of equipment really work like the movies, and how exactly they see in the dark.
This led me down a trail of research to find out the science behind IR night vision devices. It turns out that they work in two ways, depending on the night vision technology you use. Below, I will discuss the different ways they capture light.
I will also touch on various types of night vision equipment and applications. But before we dive right into these topics, I will first talk about infrared light and why it is essential to understanding night vision.
How Infrared Light Affects Night Vision?
If you want to understand night vision, it is essential to learn more about light.
Light refers to the electromagnetic radiation that the human eye can detect. This radiation encompasses a wide range of wavelengths. Shorter wavelengths contain higher amounts of light energy. In the visible light spectrum, violet has the most energy, and red has the least. Just beside the red light is the infrared spectrum.
Infrared, or infrared light, has a wavelength of around 700 nanometers to 1 millimeter. It is further divided into the three categories below.
- Near-infrared – Also known as near-IR, this type of infrared light has a wavelength ranging from 0.7 to ⅓ microns. It is also the closest one to visible light.
- Mid-infrared – It features wavelengths between 1.3 to 3 microns. Both near-IR and mid-IR light is available in various electronic devices, including remote controls.
- Thermal-infrared – Thermal IR fills in a big part of the infrared spectrum, with wavelengths ranging from 3 microns to over 30 microns. It is different from the previous two lights because the object emits it instead of reflecting it.
To make night vision work, thermal imaging monitors these infrared waves. We will discuss this topic further below.
How Does IR Night Vision Devices Work?
IR night vision illuminators work in two ways. Some devices use optoelectronic image enhancement, which captures the reflected light of objects then amplifies that into that visible glowing green color in your images. Meanwhile, other night vision equipment captures available light by detecting the heat of any object instead of their reflection.
Image enhancement is probably what most people think of when they think about night vision systems. This technology is also known as a night vision device or NVD.
A night vision camera features a conventional lens, also called the objective lens, to capture ambient light and near-infrared. These two types of light will then go through the image-intensifier tube, which amplifies them. This is done by converting the photons of light energy into electrons via a photocathode.
Once these electrons pass through the tube, the device will multiply the electrons by thousands. These new electrons will collide with the other atoms inside the tube to ultimately create a chain reaction where they leave the channel.
Near the end of the image intensifier tube, the electrons will pass through a screen coated with phosphors. The energy of the electrons will force the phosphors to release photons by reaching an excited state. These phosphors ultimately cause the familiar green image on the screen, which people commonly regard as night vision.
You can view this green phosphor image through another type of lens, called the ocular lens. It enables you to focus and magnify the frame. Additionally, the night vision device allows you to see the images via an electronic display, such as an external monitor.
Besides image enhancement, other night vision devices use thermal imaging components to record light in pitch dark situations.
In thermal imaging, a special lens captures the upper portion of the infrared light spectrum or heat of the subject. Objects emit this type of light instead of simply reflecting it. Hotter objects, such as warm bodies, release this light than cooler subjects like buildings or trees.
Once the lens scans the infrared-detector elements, it will automatically produce a thermogram. This factor is then transformed into electric impulses, which go through a signal-processing unit within the NVD.
Once this unit—usually a circuit board—finishes translating, it sends the information to the display screen. This information usually shows up in various colors, based on the intensity of the infrared emission. Ultimately, this combination of all colors produces the final image.
What Are Some Night Vision Applications?
The original application of night vision technology is to detect enemy targets at night. Today, the military still uses night vision devices, especially night vision goggles, for that purpose and for navigation and surveillance as well.
Besides the military, nature enthusiasts, hikers, and hunters also use NVDs to locate their way through the woods at night.
Meanwhile, detectives and private investigators also operate NVDs when tracking people.
Furthermore, business owners and homeowners can put up night-vision cameras around their properties to monitor their surroundings. Some security cameras use thermal technology
On top of all these common applications, law enforcement used NVDs to detect objects hidden by criminals. Thermal imaging technology can reveal when there are recent changes to the area, not otherwise obvious to the naked eye. Thus, they can effectively provide clues in several investigation cases.
Finally, filmmakers also utilize night vision equipment with thermal imaging when shooting in pitch darkness or when the script or scene requires it.
There you have it—the science behind IR night vision.
Night vision devices are especially handy when you wish to shoot in low-light conditions or see in the dark. They capture infrared, or light that is invisible to the naked eye, and amplify it to create a final image. There are two common ways to do this—image enhancement technology or thermal image for heat.
The former generates electrons to pass through a phosphorus screen, which produces the green image commonly associated with night vision. Meanwhile, the latter captures the upper portion of the infrared light spectrum to create a thermogram, which is then translated to the final image. Thus, it can translate into a digital image or video.
Hopefully, this article answered most, if not all, of your questions about how IR night vision works.