Night vision is an awesome technology that has changed the concept of viewing in the dark. Most of the people are familiar with this concept & people who haven’t heard about it, must have seen it in action movies, at least. So, what is a night vision and how does night vision work? These questions must have popped in your mind every now and then, we bet! If it has then you are in the right place.
Night vision technology has really made an impact on the life of the shooters, hunters & most importantly law enforcement officers. Before, people were unable to see what was in the dark and struggled to have a clear vision in the low light situation. Here, you will know the working principle of night vision to have a clear understanding of this topic.
Table of Contents
What is Night Vision?
Before unfolding the working process of a night vision, let’s discuss what is night vision, first.
After the sun is set, people really struggle to see any object clearly if there is no alternative light source. In the dim light situation, people can’t have a clear understanding of what is really out there and in the dark light, they simply can’t see.
Night vision technology solves all these problems for you and enhances the power of capturing everything out there in the low light as well as in the dark. Through this marvelous system, you are now able to be your own version of James Bond! So, how does night vision technology work?
How Does Night Vision Work?
Night vision technology works mainly in two different ways. The first way is the image enhancement process and the second way is thermal imaging. In the below sections we will discuss these process in details. Before that, we need to have a basic understanding of light and how it works.back to menu ↑
Humans can see better in the daytime and that’s why we work in the day and sleep at night. We have retina in our eyes which is light sensitive. This retina has two major cell namely rods and cones. Rods are expert at detecting movement in the dim light situation and cones are expert at seeing the colored light spectrum. In number we have rods 20 times more than the cones and, yet we are not able to see well in the dark!
Light is basically an electromagnetic spectrum which consists of three main parts. Those are infrared light, visible light, and ultraviolet light. The energy of a light wave is a reflection of its wavelength. The shorter the wavelength the higher the energy is. Between the visible light spectrum, the violet is the most energetic and the red is the least energetic. Just after the visible red light spectrum is the infrared light.
Infrared (IR) Light
This infrared light has three separate categories.
This is the closest to the visible light wavelength. Its wavelength ranges from 0.7 microns to 1.3 microns.
This wavelength ranges from 1.3 microns to 3 microns. These two IR categories are vastly used for remote controls and other electronic equipment.
- Thermal infrared
Thermal infrared is the longest part of infrared which ranges from 3 microns to 30 microns.
But, there is a key difference between the thermal IR and other two IR. The thermal infrared light is emitted by an object whereas others are normally reflected off the objects. This happens because of the phenomena that occur at the atomic level.
Atoms are generally in motion all the time. Even in solid objects! They vibrate, rotate and move constantly. This excitation level can vary according to the amount of energy it gets. If we can provide a certain amount of energy to an atom, which is called the ground state energy level, it will move to another excited level. To what level the atom will jump on, depends on the amount of energy applied to it through heat, light or electricity.
We can also think of this incident from an electronic perspective. As we know that atoms consist of electron, proton, and neutron. Neutron and proton consist nucleus. Electrons are orbiting the nucleus having different energy level according to the orbit, the more distant the orbit from the nucleus the more energized the electrons from that orbit are.
When electrons are energized to a certain level, they move to the upper level. But, they also want to return to the original level and whilst doing it, they release the extra energy as a particle of light called the photon. What we see is the atoms releasing photon as energy. In the night vision equipment, the thermal imaging system works through this infrared emission of light.back to menu ↑
Most of the night vision equipment use image enhancement technology. When you are talking about night vision, most people think that you are talking about image enhancement. Also, these image enhancement system is called NVDs, meaning night vision devices. These devices normally use an image intensifier tube to collect the infrared and visible light and then amplify it.
This is how night vision works for image enhancement process:
At first, the objective lens captures the ambient light as well as some near-infrared light. This objective lens is not a very complex level lens rather a very conventional one.
Next, the light captured is sent to an image intensifier tube. Then the tube gives an output of around 5000 volts which is very high to the components of the image tube.
Converting into Electrons
This image intensifier tube then converts the light into electrons through its amazing component named photo-cathode.
When the electrons are passing through the tube, similar types of electrons get released into the tube from the atom. So, the number of electrons are multiplied by a factor of thousands and that is done by a component named microchannel plate (MCP). A microchannel plate is normally a little glass disc which is made by using fiber optic technology. The disc has millions of tiny microscopic holes in it which are the above-mentioned microchannel. This MCP is located in a vacuum place having metal electrodes on both sides of the disc.
Multiplying the Electrons
Each of the channels has a length about 45 times than its width. The sole purpose of this channel is to multiply the electrons. The whole process begins when the electrons from the photocathode are hitting the MCP on its first electrode. Then it is transferred into the glass channels by the thrust of 5000 volts and is sent between the pair of electrodes.
As the electrons are passing through the microchannels, they get thousands of other electrons released in every channel. This process is named the cascaded secondary emission process which is pretty awesome. What happens is that the electrons collide with the channel side and excite the atoms and causing the release of the electrons. This released electrons then do the same trick on the channel atoms and start a chain reaction process.
As a result, there are millions of new electrons along with the original ones by this cascaded secondary emission. Most amazing is that the MCP channel is designed in an angled way, from 5 degrees to 8 degrees, so that the electrons can easily collide with the channel body. It also helps to reduce the feedback of the ion and direct light on the output side that comes from the phosphors.
At the last part of the image intensifier tube, there is a screen coated with phosphors on which the electrons hit. While passing through the channel, the electrons maintain their position in relation to each other which helps to provide a perfect image of the object. This happens because the alignment of the electrons is kept the same through its travel.
The phosphors then release photon because the energy of the electrons forces them to do. Then the green image is created on the screen of the night vision because of the phosphors.
There is also another lens called the ocular lens that helps to see the image. It also helps the viewer to magnify the image and focus it. There may be a monitor to display the image or it can be viewed through the ocular lens directly.
This process is called image intensifier as it collects the tiny bit of light available in the surrounding darkness and boosts perfectly for our eyes. But you won’t find light all the times you are using a night vision. So, what happens when you are in full darkness? The image enhancement technology doesn’t work if there is no light at all. In this situation, you need thermal imaging.back to menu ↑
In this thermal imaging system, we will look for the heat that the objects give off instead of for the light that they reflect. In general, any living thing which is moving at night is going to be hotter than its surroundings. It is also applicable to any vehicles and machines. Hot objects always give off infrared radiation that is a similar type of energy like light but has a slightly longer wavelength. So, they convert the infrared radiation into a visible image. There are many thermal imaging cameras that use different colors to indicate objects having different temperatures.
This is how night vision works for thermal imaging:
At first, a special lens focuses the infrared light emitted by all the objects.
Then, a phased array of IR detector element scans the focused light. A temperature pattern is then created by the detector elements which is called a thermogram. It’s a very detailed pattern that is created within one-thirtieth of a second by the detector array. It obtains the temperature information and thus makes the thermogram.
That information is taken from thousands of points from the field of view by the detector array. Next, this thermogram created by the detector is converted into electronic impulses.
After that, these electronic impulses are sent to the signal processing unit which is a circuit board having a dedicated chip. This chip then translates that information into data from the elements and makes it ready to display.
The signal-processing unit immediately sends that information to the display unit where it can be seen as different colors. Those colors will depend on the intensity of the IR emission. The whole image is created by combining all the impulses from all of the elements.
The thermal imaging devices available in the market can scan at a rate of 30times/second. In general, they can sense temperatures that range from -20 degrees Celsius to 2000 degrees Celsius! They can also detect the temperature change of about 0.2 C.
Thermal Device Types
In the market, there are two types of thermal imaging devices. The first one is the un-cooled one. It is the most common type among the devices. These types work perfectly at regular room temperature. It is completely quiet meaning it does not make any sound during the operating process. It is activated immediately and, also has a built-in battery system.
The second category is the cryogenically cooled one. This type is the expensive one as it offers some extra advantages. Also, it is more likely to get damaged from rough use. The elements of this system are sealed inside a container that is cooled down to 0 degree Celsius! It offers the best resolution and sensitivity that is resulted from cooling the elements. It can detect the temperature difference of about 0.1 degree Celsius from a distance of 300m! This is amazing.
Thermal imaging is great at detecting objects in a pitch-black situation. Although, most night vision devices are made of on image enhancement technology.back to menu ↑
Why is Night Vision Green?
You may sometimes wonder that “why is night vision green”. Well, the photons carry all the colors at night when they are absorbed at night. However, when the components of the devices convert these photons into electrons, they lose their original color and only black and white is left. As our eyes can have a long look without any discomfort to green light, the phosphors help the black and white image to present before us as green. That is why it looks green.back to menu ↑
Night Vision Generations
For more than 40 years, night vision devices are around. There are many different night vision generations. Whenever any new technological advancement was made, a new generation was introduced to the market. So, what are the generations?
The United States Army introduced the first-night vision into the world war ll. They used the active infrared system. They did that by attaching an IR illuminator to the night vision devices. These were basic techniques. Those systems used the anode connected with the cathode to accelerate the electrons. However, the images distorted and the life cycle of the tube was not very big. In addition, advancement of the hostile nation’s weapon was a major setback for the gen 0 devices.
The generation 1 devices used passive infrared instead of active infrared. They used the ambient light of the moon, star and made a very good use of it. Whilst doing it, they did not require any projected infrared light source. However, when there was no moon or other light sources, the gen 1 could not do anything. That was a major setback for those devices. Its image intensifier tube was the same as the gen 0 type.
After that, there was a vast improvement in the gen 2 category. The performance and resolution of the new generation improved quite a lot from its previous version. The most exciting features of this new generation were to see in the very dim light situation. When there was moonless night, the devices still worked. The awesome microchannel plate was a nice addition to the component list. The images were very good and the final product was clear.
The US military uses this generation today. It is quite the same as the generation 2. However, the resolution and the sensitivity are much better. That happened because of the use of gallium arsenide. This thing is good at converting the photons into electrons very efficiently. Also, the MCP has a longer life cycle because of the coating with an ion barrier.
The basic difference is the removal of the ion barrier. That helps to make it less noisy and improved the signal to noise ratio. Besides, more electrons can reach the amplification stage. As a result, the image quality gets better and better. There is an addition of an automatic-gated power supply system. This new technology is very good at performing well in lighting conditions when they fluctuate. Therefore, the new generation 4 is the ultimate product that the modern technology offers you!
When you are having any bargain devices, you can be sure that those are using either gen 0 or gen 1. You will be disappointed when you use those things, as they do not offer much. The modern devices are a bit pricey but they are handy items.back to menu ↑
Night Vision Equipment
There is quite a lot of equipment that people use as night vision. The most important categories are:
- Night Vision Scopes
These are very popular among the shooters and hunters. They are monocular items. They can mount on the rifles and can help you for taking the game at night.
- Night Vision Goggles
These items are normally handheld. There are monocular items as well as binoculars. They are very good for a constant viewing of the night.
- Night Vision Cameras
Cameras can send the night vision image to a monitor or VCR. People use them in buildings for security purposes. The newest camcorders have built-in night vision technology with it. In-depth knowledge can be acquired by being a member of NV forums found online.back to menu ↑
People introduced the first-night vision devices for locating the enemy at night. Still today, they use those items vastly in the army. To know how does night vision work is very important when you are out there in the field. Either you are in the military or in the outdoors for shooting or hunting, you need to use them properly. Hope this will help you to have a basic knowledge of night vision.