For many, the thought of night vision conjures up images of Special Operations Forces slipping into an enemy compound under the cover of night to rescue hostages or take out a heartless terrorist, their way made clearer by goggles and scopes that turn darkness into green light visible only to the person wearing them.
And though this is one aspect of night vision’s use, it does little to explain how night vision works.
What Is Night Vision?
Simply put, night vision is the ability to see beyond the normal boundaries of visible light. Now, I know that sounds a bit elementary, even like a fool’s answer, but it is true nonetheless.
Human beings have been blessed with many wonderful abilities, but seeing clearly in the dark is not one of them. We see best in the light, or rather, when the light is bright enough. However, light is always present, even in darkness, but not all light is visible to the human eye. The two types of light present in darkness are often referred to as infrared light and ultraviolet light. To best illustrate, let’s look at a diagram of what scientists call the electromagnetic spectrum.
Visible light to the human eye is located in the center of the light spectrum. Infrared light and ultraviolet light are located on either side of visible light and are not visible by the human eye under normal conditions. In order for us (human beings) to see at night, we must have some sort of external device that detects and amplifies unseen light to the point that it is visible to us. That’s where night vision devices (NVDs) like the Night Owl NOXM50 Night Vision Monocular come in.
How Do Night Vision Devices Work?
Well, the non-technical answer to this question can best be summed up this way. Night vision devices are capable of detecting infrared light which is invisible to the human eye. Then through a process of enhancement, convert this into visible light.
NOTE: Don’t confuse image enhancement with image magnification. The first deals with light, the latter with size.
Too simplistic for you? Then how about this? Take a look at the diagram below of the intensifier tube from a night vision device : (Image courtesy of How Stuff Works)
You can see by this diagram that the image prior to light amplification by the night vision device is considerably darker and harder to define. But once the device captures the available [invisible] infrared light photons, the photons get converted to high-energy electrons, and are then multiplied into more electrons before being converted back to [visible] photons of light. The result is many more photons, which in turn provide visible light for us to see in the dark. That’s it, really. That’s how night vision works; how light is amplified enough for us to see clearly at night through a night vision device.
A Matter Of Generations
Before I get into the different Generations of Night Vision, I need to define two terms for you: active infrared and passive infrared. In fact, let me see if I can illustrate both at the same time, the different generations and the two different types of infrared technology.
Active infrared devices require an external projection unit – commonly called an IR illuminator – to project a beam of invisible infrared light onto an object in order to capture enough of this light to be seen by the device. These were the original Generation 0 NVDs used in WWII. Active infrared can still be found, but usually as an option on passive IR devices.
Passive infrared devices (Generation I, Generation II, and Generation III) make use of available infrared light found in a tiny amount of ambient light – such as starlight and moonlight – instead of an IR illuminator.
A common problem with passive IR devices is that they don’t work well on moonless or cloudy nights; but when they do have available ambient light, they work incredibly well. Generation II and III devices have countered this problem with the use of a Microchannel plate (a powerful amplifier), making it possible to see in extremely low light conditions. In addition, as mentioned earlier, many of the Gen I, II, and III NVDs still come with an attached IR illuminator for use in extreme conditions where ambient light is completely non-existent.
NOTE: Generation IV technology does exist, but the cost of this technology puts it out of the range of most consumers. Gen IV technology is top-of-the-line, used by American military forces and some law enforcement agencies with deep pockets and life-threatening missions. For that reason, we won’t be discussing Gen IV here.
The Digital Age
Night vision has not been immune to digital advances. Digital NVDs utilize advanced computer technology similar to that in digital cameras, rather than traditional intensifier tubes.
Light sensitive circuitry now senses and enhances the tiny amount of infrared light found in ambient light at night. And typical to digital components, many useful programmable adjustments are possible making this technology ever more versatile.
The most significant benefit of digital NVDs is their low cost to produce. This translates into a low price for you to purchase. Commercial law-enforcement grade devices such as the Night Owl iGEN 20/20 Night Vision Monocular now cost hundreds of dollars compared to thousands you need to spend for all but Generation 1 devices.
Well, that’s it. Hope I’ve answered your question: What is night vision and how does it work? If not, or if you have any other questions about night vision technology, please contact me.