We usually hear the term 'night vision' being used repeatedly in fictional spy movies. Each time the protagonist gets engaged in a gun fight in total darkness, he would gain perfect view of his surroundings with his equipped night vision devices and completely wipes out the whole stage. But the question is, do night vision devices really live up to its reputation in real life? The answer is yes and no. We'll explain the answers why in this guide but first we will go through the basics with you so that you'll be able to grasp the whole picture in no time.
Inside a Night Vision Scope
We do know that night vision oculars are capable of detecting visions even in the darkest night. But don't we wonder upon the unique mechanism of a night vision eyepiece that makes up to its functionality? Well, we'll have you covered as we'll guide you through the characteristics and mechanism of a night vision device in the section below:
Night Vision is a term defined as the ability to gain visual in low light conditions. In low-light conditions, our naked eyes are unable to gain sight of the surroundings without sufficient visible light entering the retina. Thus in order to gain vision, night vision devices employ a unique system to on capturing more light to maximize vision in the darkest night.
A simple night vision device mechanism requires 3 vital components, which is a set of optic lenses (objective and eyepiece lenses), power supply and image intensifier tube. Both optic lenses serve its purpose to focus and magnify light rays respectively. The power supply, on the other hand, generates power inside the image intensifier tube to create an electrostatic field for electron acceleration. The image intensifier tube is the main and most complex component of a night vision device. An image intensifier tube is made up of microchannel plates, photocathode and a screen made of either phosphor or gallium arsenide. All these components help to absorb and amplify electrons to produce a night vision image.
Generally, night vision mechanism works by utilizing infrared light spectrum to obtain clearer images in surroundings with low illumination. First, light illuminations from infrared illuminators or ambient light from surroundings (eg. moon, stars, etc.) are gathered and focused into the objective lens. The photons from light sources would be converted into electrons via photocathode in the image intensifier tube. As the electrons travel through the intensifier tube, the electrons would be greatly amplified by microchannel plates in the tube. The amplified electrons would then hit the back phosphor or gallium arsenide screen of the image intensifier tube, converting the electrons into light image.
Night Vision Device Characteristics & Usage
As shown in the figure 1.2, images generated by night vision device would appear to be of monochromatic green hue. Besides, night vision images would not be as clear as those of daylight scopes because the image are projected indirectly through a phosphor screen. It is to be noted that dark spots may present in Generation 1 Night Vision tubes. The figure above shows ways to identify different spots and zones in night vision devices. These spots are due to natural manufacturing process of the intensifier tubes and do not affect the night vision performance.
Keep in mind that most night vision optics are designed to be used in low-light conditions only. It is not advisable to use your night vision optics in daytime or bright light conditions. Direct contact with bright light will damage the interior components of the night vision devices. On top of that, devices may suffer from damage due to prolonged exposure to high humidity level. In order to reduce damage caused by these conditions, few manufacturers have installed electronic light sensing systems into its night vision optic devices. These systems provide protection by automatically switching off overloaded circuits caused by excessive light intake. Besides that, almost all night vision optical devices are pre-installed with systems that shut down automatically when not in use to maintain its lifespan. While switching on certain night vision optics device, it is to be noted that the device may produce certain level of 'buzzing' sounds intended to remind users to switch off the device when not in use. Nonetheless, it is recommended to remove the batteries and store your device in a cool dry place if you're planning to store them for a long period of time.