Learning how image intensifier tubes work can be very beneficial, as it helps the end user understand what to expect from the device in terms the capabilities which are based on specific design features and choices characteristic of each modern IIT.
In this article we aim at explaining is a simple and easy way, the inner workings of such technology
The anatomy of IIT’s
Image intensification is a process that allows us to amplify ambient light, multiplying it by thousands of times, allowing us to turn darkness into visible images.
An IIT is generally made up of three main components that allow us to break down the inner workings of the device into 3 easy to understand steps.
The Photocathode
Our fist component is going to be the photocathode, which essentially is a membrane that when charged negatively with electric current, is able to turn light (photons), into electrically charged particles (electrons), thanks to Einstein’s “Photoelectric Effect”.
Micro Channel Plate
The MCP is the second component and one of the greatest breakthroughs in night vision tech, as it allows us to multiply electrons, thus amplifying light in the end.
It is essentially a membrane peppered with millions of microscopic holes, so called channels, in which electrons pass through and bounce around, thus creating more and more electrons at each bounce, virtually multiplying the total amount by thousands of times.
Phosphor Screen
Since human eyes are not able to detect electrons, our brain is not capable to process them as visual information, thus a need to turn electrons back into photons, which are visible to humans as light.
Because of this, right after the MCP, a Phosphor Screen is installed in position, which is able to turn electrons into photons.
The phosphor screen is yet another membrane, containing phosphorescent chemicals, which, when hit by electrons, and positively charged, is able to create light, in the form of photons.
The color of our image is directly dependent on the kind of phosphor contained in the PS, and this is why in the modern day and age, night vision devices come mostly in green (P-43 green phosphor) or white (P-45 white phosphor).
Tube Protection Mechanisms
When too much electromagnetic radiation, in the form of light enters an IIT, components such as the MCP or PS, may get damaged if precautions aren’t taken in advance.
This damage shows in the form so called “blems”, dark spots or shadows, which may be permanent and unrepairable, wasting thousands of dollars’ worth of gear, and potentially resulting in a divorce if your significant other finds out you dropped $4000 CAD, only for that to become ruined.
Because of this, the implementation of protection systems embedded into the IIT, is crucial to safeguard equipment, safety and efficiency of the operator.
The following systems are integrated in all modern Gen 2+ and Gen 3 systems that we offer on our website (link tubes)
Automatic Brightness Control [ABC]
Automatic Brightness Control or ABC, is a safety mechanism that will automatically lower voltage to the MCP, in order to reduce the number of flowing electrons, reducing the risk of damaging the phosphor screen. This is a very simple yet effective way to keep the device running, in conditions where it’s not dark enough to have the system running on maximum brightness safely, but still dark enough so that it is hard for our eyes to see without NV.
ABC works the same as Automatic Gain Control, but only kicks in to protect the tube from light damage, while AGC is a feature that regulates tube gain constantly to keep brightness at a comfortable level for the wearer. AGC is not present on Manual Gain Systems such as the MH-1 or PVS-14, which give the user the possibility to dial in the perfect gain level, enhancing accessibility.
Both systems are available on our website at: MH-1 and PVS-14
Bright Source Protection [BSP]
BSP is arguably the most effective safety feature, and just like ABC it is present in all modern IIT’s, with the exception of Auto-gated tubes.
BSP will kick in, in the event that light levels are too high even after ABC sets gain to the minimum level, and it works by cutting down voltage directly to the Photocathode, making for an extremely safe and robust protection mechanism. The downside to this is that resolution will drop immediately when this is into effect.
A common misconception is that tubes without auto-gating will get damaged more easily when exposed to high light, but this is untrue because BSP is extremely effective at protecting the IIT.
For this reason we offer NVT-4’s and NVT-5’s non-autogated Image Intensifiers on our website
Auto-gating [AG]
Auto-gating is the most commonly used protection mechanism in modern high-end IIT’s, since it brings some pretty amazing advantages over BSP. AG works by turning the tube on and off thousands of times a second by inverting the polarity directly from its internal PSU.
What this achieves is prolonging the life cycle of the tube and more importantly, it protects the tube from intense light sources while still maintaining high resolution unlike BSP.
You can check out our vast range of autogated tube options on our website (link)