How Night Vision Works...

Wondering How Night Vision Works? Well, if your anything like me you probably have wondered at one time or another. As far as night vision goes I think the question of “Does night vision really work?” has been answered many years ago when night vision became available to the public and no longer became a secret agent or military only tool of the trade.

With the proper night vision equipment you can see a person or object at a distance of 200 yards (183m) on a moonless, cloudy night!

There are two very different ways that night vision can work for you, depending on the type of technology used in the night vision equipment. In this article, we will be discussing and “bringing to light” those two technologies so you can make an educated choice in purchasing you night vision equipment.

How Night Vision Works...The two technologies at a glance:

1. Image enhancement – Works by collecting small amounts of light from the light spectrum that we all see, in addition to light from the lower portion of the infrared spectrum that is present, but not perceivable by our eyes. It takes this small amount of light information and amplifies it to point that we can see the subject or object.

2. Thermal Imaging – Works by collecting the upper portion of the infrared light spectrum which translates into heat instead of reflected light. Objects that have a higher temperature, such as the human body or a hot car engine will emit more of this light from the upper infrared spectrum than something cooler such as, a rock or a building.

To understand How Night Vision Works it’s important to understand a little about the properties of light and how we perceive it in everyday life. The amount of energy in a light wave is related to its wavelength…so a shorter wavelength has higher energy. In the visible light spectrum Violet light has the shortest wavelength so it has the most energy. Red light is the exact opposite of Violet with the longest wavelength and the least amount of energy.
Infrared is the small part of the light spectrum that we can NOT see and is positioned right next to the visible light spectrum, as you see in the graphical reference below:

Infrared light is split into three categories:

1. Near-Infrared (near IR) – which is the closest on the spectrum to visible light, having wavelengths that range from 0.7 to 1.3 microns (700 billionths to 1,300 billionths of a meter)

2. Mid-Infrared (mid IR) – which is positioned in the middle portions of the infrared spectrum, having wavelengths that range from 1.3 to 3 microns.
NOTE: Both Near and Mid Infrared are used in many different electronic devices, such as remote controls.

3. Thermal Infrared – (thermal IR) which take up the most space on the infrared spectrum, having wavelengths that range from 3 microns to 30 microns.

To understand the key differences between thermal IR and the other two is to realize that thermal IR is EMITTED by an object, whereas Near IR and Mid IR is REFLECTED by an object. To understand why thermal IR is emitted and not reflected we must drop down even further to the Atomic Level.

Some of you might be having flashbacks of your high school science class at this point, but I promise this will be short recap and we will be moving on to how this translates into purchasing the right night vision equipment for you shortly.

Atoms, as you may remember, consist of a Nucleus that contains the protons and neutrons and the electron cloud. A simple way to look at this is the think of the electrons in the electron cloud circling the nucleus in different orbital paths.
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While the electrons don’t take the same orbital path on a consistent basis it does help to visualize the different orbital paths of the electrons as different energy levels, that as we excite the atom by applying heat, light or electricity the electrons orbital paths move further from the Nucleus, or a higher energy orbit.

Ok here’s where the magic happens….this electron really wants to be back in its grounded state, close to the nucleus. To do this, it must release all this energy that was forced upon it, so when it does release this energy it releases as a photon which is a particle of light (I can’t remember, which Sci Fi movie was the Photon torpedo used in?)
Anyway, you can actually see this happen with your own eyes, which I’m sure you do on a regular basis. And simple, very common occurrence is the heating element on a toaster or oven. When it turns bright red or orange this is the atom becoming excited by the heat and the electrons releasing the heat energy it is collecting and releases red photons.How Night Vision Works How Night Vision Works How Night Vision Works H

To sum up…This emitted energy, the photons, also have a very specific wavelength or color that is dependant on the electrons energy at the time the photon was released. Living things and even inanimate things all use energy at some level. And energy consumption generates heat which causes the atoms in the object to become excited and release photons into the thermal infrared spectrum. The hotter the object the shorter the wavelength of the infrared photon it releases, if the object gets very hot it will begin to move into the visible spectrum starting with red and moving to orange, yellow, blue and eventually white.

Well that wasn’t too bad was it? Now we will see how Night Vision Thermal imaging takes advantage of all this infrared light being emitted from objects.

Now we’re getting down to business….Here’s how Thermal imaging Night vision works.

1. The lens focuses the infrared light emitted by the objects in view through the lens.

2. The focused light is scanned by a phased array of infrared detector elements within the unit. The detector elements create a detailed temperature pattern that is called a thermogram this process takes only a fraction of a second and maps thousands of points on the field of view, or what your focused on with the unit.

3. Now the thermogram that was created is translated into electric pulses, which are sent to the signal processing unit (the circuit board with a dedicated microprocessor chip that translates these electric pulses into data that can then be transferred to the display or the unit

4. Once the signal processing unit sends the data to the display where it can be viewed as different colors depending on the intensity of the infrared emission from the objects that are focused upon by the unit. This combination of infrared emissions translated into color creates the image we see.

Thermal image of ceiling indicating water damage

Most thermal imaging devices can scan the objects focused on by the lens of the unit at a rate of 30 times per second and can detect temperature variations ranging from -4 degrees Fahrenheit (-20 degrees Celsius) to 3,600 degrees Fahrenheit (2,000 degrees Celsius) and can detect changes in temperature of about 0.4 degrees Fahrenheit (0.2 degree Celsius) Now we need to break down thermal imaging into two categories:

1. Un-Cooled – This is the most common. It operates at room temperature and is completely quiet, activates immediately and has a built in battery.

2. Cryogenically Cooled – this is much more expensive than and not as rugged as the un-cooled version. These units have elements that are completed enclosed and cooled to a temperature below 32 degrees Fahrenheit (0 degrees Celsius). Although, there is an advantage to these units…they have incredible resolution and sensitivity due to the cooling process. This increased sensitivity allows the units to detect the difference between an objects temperature by as little as 0.2 degrees Fahrenheit (0.1 degree Celsius) from more then 1,000 feet (300 m) away. In other words…you won’t have problem noticing the fact that that person 1,000 feet away from you is holding a gun!

Well, as you can see night thermal imaging is excellent for distinguishing people from objects and working in almost absolute darkness. And may be what you’re looking for…but most night vision uses night vision utilizing the image enhancement technology that is distinguished by the erry green images that we have all come to recognize. Now, on to image enhancement technology…

Image enhancement technology is the most popular in the night vision equipment world and actually Image-enhancement systems are often referred to as night vision devices (NVD’s)

The core component of the NVD’s is called the image-intensifier tube, which collects both infrared and visible light and amplifies it to a level we can easily perceive with our eyes. Here’s the step by step breakdown of how it works:

View a Flash Animation of How night vision works here.

1. A lens, also called the objective lens gathers all the ambient light and some near-infrared light and sends it to the image intensifier tube.

2. Powered normally by two N-cell or AA batteries, the image-intensifier tube output's about 5,000 volts to the components of the image-intensifier tube.

3. The first component in the tube that the electrons pass through is the photocathode, which basically turns the photons of light energy into electrons.

4. After passing through the photocathode, the, newly converted electrons, pass through the image-intensifier tube and similar electrons are released from atoms in the tube, multiplying the number of electrons in the tube by a factor of thousands through the Micro channel plate (MCP) in the tube.

The MCP is a tiny, glass disc that has millions of microscopic holes (micro channels) in it, made using fiber-optic technology. This MCP is contained in a vacuum and has metal electrodes on either side of the disc. Each of the micro channels is 45 times longer that they are wide, and works as an electron multiplier. Let’s take a little more time to explain how this happens…When the electrons hit the first electrode of the MCP, they are accelerated into the glass micro channels by the 5,000 volt busts being sent between the two electrodes of the MCP.

As the electrons pass through the micro channels they cause thousands of other electrons to be released in each channel using a process called cascaded secondary emission. Basically, the original electrons collide with the side of the micro channel, exciting atoms and casing other electrons to be released. These new electrons also collide with other atoms, creating a chain reaction that results in thousands of electrons leaving the channel where only a few entered. An interesting side note fact: the micro channels in the MCP are created at a slight angle to encourage electron collisions and reduce both ion and direct light feedback from the phosphors on the output side.

5. The last component of the image intensifier tube the electrons pass through before reaching the final lens is the phosphor screen. It is a screen coated with phosphors [definition here] When the electrons hit the phosphor screen the maintain the same position they were in when they left the micro channel they first entered, so this results in a perfect image due to the original photons that entered the lens of the NVD not changing alignment while passing through the image intensifier tube.

6. So what about that green image, you ask, where does that come from? Well, when the electrons pass through the phosphor screen, it causes them to become excited and release those good ole’ photons we now know and love. The phosphors in the screen are what cause the green image we have come to know as night vision.

7. Finally, the green phosphor image is passed through the final lens, the ocular lens, which allows you to magnify and focus the image as you view through the ocular lens. You of course could also connect the NVD to a monitor or camera for recording or viewing

Well, now you have should have a good basic understanding as too how night vision devices work. We can now safely move on the selecting the proper piece of equipment that will work the best for your particular need or situation.