Night vision is a concept discussed by scientists worldwide for many years. Naturally, its "bird's eye" language is woven of incomprehensible formulas, turns, terms, and complex inferences. We will try to consider this question in a simplified and understandable for our form. Let's start with an ordinary domestic cat, whose vision is undoubtedly built in some unique way. When you begin to understand a cat's life, you are surprised - at a distance of more than ten meters, they see badly. So how do they hunt, and how does night vision help them retain their title of a skilled night hunter? Firstly, the cat is endowed with a unique eye lens structure. Secondly, the anatomical structure of its eyeball is hidden deep in the eye socket, and the visual field reaches more than two hundred and fifty degrees within a radius of ten meters; they are super sensitive and enjoy stereoscopic vision. And the cellular structure of the retina's DNA adds to this animal's ability to see perfectly at night. However, oddly enough, there are at least two types of supersensitive cells in the cat and human eye, thanks to which we feel the fullness of the worldview. These are the so-called cones and rods. The first ones are responsible for the varied daytime palette of colors, and the second ones provide orientation in the twilight. Expecting a reasonable question, why in this case, a man is not a cat, we clarify. Thanks to nature and the creator of this world. The human eye "got" a retina with scattered sticks, and proximity to each other improves vision. In the cat's version, these same sticks are deployed in a specific way forming microlenses, contributing in dusk to capture minimal light, "gathering" it together and in one direction. Such amplification makes it possible to increase visual acuity in the darkness at least ten times more than ours. It is a simple principle of normal night vision, which many animals use, and a man, having studied this phenomenon, invented many kinds of equipment for himself.
Who and when invented night vision?
The desire to navigate in the dark, and even more so to perform specific tasks in military conflicts, gave the possibility to have a tangible advantage to the one who owns the technology. At the end of the nineteenth century, the German scientist, Nobel Prize winner, and founder of quantum physics Max Planck derived the formula for energy distribution in the spectrum of a black body, which subsequently made it possible to study thermal radiation and gave its theoretical basis, followed by the discovery of infrared rays. Therefore, almost all reputed institutes working for the military industry were, and still are, engaged in the development of night vision devices. The first timid successes in night vision systems date back to the beginning of the last century. To the prototype of thermal imaging technology - the evaporograph apparatus. This apparatus functioned by using a sophisticated system to measure the temperature difference between the observation object and the surrounding background using a particular oil film, which, when heated, evaporated unevenly and recorded the difference in thickness. The beginning of the twentieth century impeded the development of infrared technology. A new direction in science appeared - spectroscopy, where they actively began studying spectral types of radiation, temperature, and density.
Most importantly, the possibility of the remote and non-contact study of objects. This was a breath of fresh air for astrological scientists. Instruments for radiometric measurement of temperatures of stars and planets appeared. And, of course, it did not pass by the military developments of infrared detectors for detecting objects - cars, ships, boats, people, and so on.
There were many developments in this direction. Infrared systems of passive type were used, using a thermowell and a galvanometer, radiation receivers made of lead sulfide, and other variants, which stopped at this stage. The breakthrough in the development of thermal imaging referred to the forties of the last century when the first samples of electron-optical converters were made, based on which, at the beginning of World War II, British aircraft began to install "friend-or-foe" recognition systems. American and German military developed night vision devices based on electron-optical converters with their installation on tanks for night driving and sights for small arms. Powerful searchlights with light filters provided night visibility up to one hundred meters. The night sight worked almost as well.
At this stage, night vision was formed and used in its so-called "active" mode, when the devices used search beams to find the object, which is a clear disadvantage. This accelerated the development of new photon-sensitive detectors for "passive" search thermal systems working without search beams. All programs were carried out strictly for the military industry and precisely. And only in the sixties of the last century was it partially allowed to use thermal imaging for civilian purposes. The American company Barnes, which produced an onboard thermal imager with optical-mechanical scanning for airplanes, is considered the beginning of the wide broad application of thermal imaging technology. A few words here are a good idea to discuss the thermal imaging camera and how it works. It's simple. All objects emit heat. The infrared imager detects this background, and after processing, it transmits the thermal image of the object to the monitor, where we can see it in the thermal projection. From dark blue to light and dark red, cold objects are in blue, and hot things are in red.
It is worth noting that in the seventies of the last century, the Swedish company AGA entered the market with an infrared-red thermal imager for civilian enterprises with a "portable" model and replaceable optics, a built-in temperature sensor with the ability to record thermal images on a videotape. The device weighed over thirty kilograms. A few years later, the firm replaced the infrared receiver with liquid nitrogen with a thermoelectric processor and launched a new model, which reduced its weight by a factor of five. And at the end of the last century, this Swedish company realized the dream of many telescope manufacturers by producing a two-kilogram portable model with a thermoelectric refrigerator and an infra-red TV system. At the same time, two world-renowned infrared manufacturers, the American FLIR and the Swedish AGEMA Infrared Systems, merged to create the world's largest company to produce a wide range of commercial thermal imaging cameras.
What about green vision?
Why green vision and not blue, yellow, or orange vision? What is the secret, and how does it work? The answers must be sought in the image, not in our eyes. And this is a very complex mechanism of the human body, which consists of the outer vascular membrane and retina. Each performs a different function, providing vision. Everything we see around us is displayed on the retina, mainly its central part, where most of the visual cells, commonly called cones, are located. In addition, all objects must be brought into focus, for all things must be brought into focus, which is responsible for our internal lens, up to eighteen diopters called the lens. By the way, like all dioptric devices, it dims with time. For our understanding of color, as we have already noted earlier, cones and rods are attractive, providing our perception of the whole daytime color palette and being able to feel normal at dusk. Based on this, the color period involved only cones, which in our eye are three kinds, each responsible for its color. "Red" cones perceive long wavelengths, while "green" and "blue" cones perceive medium and short wavelengths, respectively. Remember that when considering the concept of "brightness of light," there are two values-physical and biological.
We, perceiving biologically electromagnetic vibrations with "colored" cones, do not see X-rays, ultraviolet, high-frequency, and others. This is the essence of the natural phenomenon to protect fragile and vulnerable eyes from intense and traumatic rays. Here we come to the main topic of red night vision. ExpertsExperts refer to green as "color blindness" or "Protanopia," and red is referred to as "Deuteranopia. People with Protanopia, like most mammals, are not sensitive to long-wavelength light. And if you use red light in the long wavelength range to observe wild animals at night, you can rest easy - they can't see you. This is the principle behind the design and manufacture of night vision devices for unobtrusive driving and observation.
The invisible becomes visible. The development of infrared radiation, embedded in peaceful devices for radiology, biology, and medicine, has given an invaluable impetus to diagnosing various diseases. Their most excellent application, however, was in the military industry. This industry has evolved at an accelerated pace over the past half-century. In the beginning, whoever had the advantage of seeing in total darkness, despite various natural disasters, received a "bonus" in the form of victory. After all, practically all kinds of troops - reconnaissance, tanks, special forces, pilots, and naval forces - were involved. For example, most aviation missiles were equipped with devices with infrared-red radiation. It is fair to say that the defenses were just as effective in countering the means of attack by developing appropriate weapons for protection. However, let us return to red light in night vision devices. You will have a question about why blue light spreads in the long-wave range, and the "attachment" of the ye sticks to this color is not used for night vision.
Nevertheless, it has been proved that any color, not counting red, does not allow to work comfortably at night. That is why green is used in almost all military night vision devices. However, it is human nature to have doubts. And if your body is unique and "rebels" against red, make a simple express test. Look at the color. You see it, so the rods are depressed brightness and cones in action. You see a dark gray environment around you - the rods are "turned on." So the color for night vision devices was chosen after analyzing the raw data of different shades in a monochrome image at night. The choice was made in favor of the most distinguishable color-green. For the green phosphor glow, energy consumption is less than, for example, in white light and the rapid transition from white to dark. The eyes adjust to darkness more efficiently and comfortably with a green glow. This, of course, is not all of the benefits of green. We can add that it makes our eyes less tired, distinguishes shades, focuses more clearly on the object of observation, and so on. At different times in the development of night vision systems, scientists analyzed all this, and the military put it into practice, choosing the best one. In this case, we are talking about the evolution of the growth of "night vision." Here it is appropriate in a few sentences to describe the night vision device, which is supposed to glow green. It consists of a lens, an electro-optical transducer, and an eyepiece, which amplifyamplifies the light that enters it and captures invisible infrared waves making them visible. Since the first development of night vision devices, manufacturers didn't bother with names and don't bother now. All night vision devices are divided into generations. The first ones were "zero," weighed almost fifty kilograms, and were equipped with an electro-optical converter with an optical sight and an infrared illuminator. The infra-red beam was directed to the observation object, reflected from it, returned, and showed it through a unique lens. In the first generation of instruments, the signal at the input was amplified hundreds of times, using electro-optical transducers to boost the moon's and stars' light, thus obtaining an image. Although in bad weather, the device did not work without the electro-optical amplifier when the night sky was covered with clouds. The second generation is the most successful, with improved night vision devices. It was a breakthrough in the night vision system. Machines began to use microchannel plates in the electron-beam amplifier, which made it possible to improve the quality of the image and work in complete darkness without any backlight. The third generation differs little from the second, except for projecting a higher quality image. It used gallium arsenide, accelerating the process of converting photons into electrons. For the fourth generation, there is no good or bad light. The new portable amplifier technology automatically controls the photocathode voltage, which makes it possible to adjust to any change in light. In this generation, technology has switched painlessly from total darkness to light.
When using green backlighting, we improve visual acuity and can also understand the separation of the constituent parts of the color spectrum. Unless, of course, you suffer from color blindness.