During the day, our human eyes can see the natural scenery because they receive the direct sunlight or scattered light reflected from their surfaces. At night, because there is no sunlight, the human eye can not see the natural scenery. However, in most nights, there are still moonlight, starlight and atmospheric glow, and the surface of natural scenery still needs to reflect these weak lights, so our human eyes can vaguely see the outline of nearby scenery and large scenery. "Dark night", the sky is still full of light, which is the so-called "night sky radiation". The night sky radiation comes from natural radiation sources such as the sun, the earth, the moon, the planet, clouds, and the atmosphere, but its illumination is too weak (lower than the human visual threshold), which is not enough to cause the human visual perception. The basic ideas to solve this problem are as follows: ① use a large-diameter telescope to get as much light energy as possible; ② Like electronics, try to magnify the weak light image; ③ Use infrared searchlight or infrared flare to illuminate the scene; ④ Thermal imaging is realized by using the radiant energy of the scene in the infrared band. Using different technologies to solve this problem has formed different night vision methods.

It is the core task of LLL night vision technology to enhance the night weak light radiation to the level required by normal vision. Low light level night vision technology is committed to exploring the acquisition, conversion, enhancement, recording and display of target image information at night and other low illumination. Its achievements are concentrated in the effective expansion of human vision in time domain, spatial domain and frequency domain. In terms of time domain, it overcomes the obstacle of "night blindness" and makes people move freely at night. In terms of airspace, it enables the human eye to realize normal vision in low light space (such as basement cave and tunnel). In terms of frequency domain, it extends the visual frequency band to the long wave region, so that human vision is still effective in the near-infrared region. Militarily, low light level night vision technology has been used for night reconnaissance, aiming, vehicle driving, photoelectric fire control and other battlefield operations, and can be combined with infrared, laser, radar and other technologies to form a complete photoelectric reconnaissance, measurement and warning system. Low light level night vision equipment has become an important part of military weapons and equipment, and is also widely used in astronomy, public security, aerospace, marine and other fields.

Low light level night vision technology is a technology that uses electric vacuum and electronic optics to realize the conversion of photon image to electronic image to photon image. In the process of conversion, the enhancement of photon image is realized through the enhancement of electronic image, so as to achieve night observation under weak light illumination. The core of LLL night vision technology is LLL image intensifier, which is a photoelectric vacuum device composed of photocathode, electronic optical components and fluorescent screen. Its working principle is: the weak visible light and near-infrared light reflected by the scene converge on the photocathode, and the photocathode is stimulated to emit electrons. In this process, the light intensity distribution image of the scene is transformed into the corresponding electron number density distribution image; In the electronic optical components, thousands of electrons can be output by inputting one electron. Therefore, the electron number density distribution image of the photocathode is enhanced thousands of times. The so-called "low light level image enhancement" is realized in this process; Finally, after a large number of multiplied electrons bombard the fluorescent screen, the transformation from electron image to photon image is realized, and the enhanced low light level image is obtained for human eyes to observe.

At the initial stage of the development of low light level night vision technology, the core device used is the near-infrared image converter, which can be regarded as a low electron multiplication efficiency low light level image intensifier. It uses the silver oxygen cesium photocathode in the high vacuum to convert the infrared radiation image into an electronic image, and then through the fluorescent screen, the electronic image is converted into an optical image that can be observed by the human eye. The principle of photon electron photon mutual conversion is the theoretical basis of modern low light level night vision instruments. However, when using an infrared image converter to observe, it is necessary to use an infrared searchlight to actively illuminate the target to improve the observation distance. Therefore, this device is also called an active infrared night vision device. It was initially applied in the Second World War.

The active infrared night vision system has clear imaging and good contrast, but it needs infrared light source, which has some disadvantages, such as poor concealment, easy exposure, large energy consumption and heavy power supply device. People naturally think of using the natural low light level in the night sky to study the passive low light level technology, so that the target under the weak illumination becomes visible, thus developing the low light level night vision technology.

At present, low light level night vision systems using low light level night vision technology can be divided into two categories: low light level night vision instrument (direct observation type) and low light level television (indirect observation type).

Svtonghd-syl1 high-definition low light level night vision technology independently developed by Shenzhen shiyutong Technology Co., Ltd. adopts super star light level night vision full-color image NIR. Advanced technology greatly improves quantum efficiency, increases sensitivity by 31%, reduces reading noise by 16%, and reduces dark current by 46%. Svtonghd-syl1's original back illumination structure can avoid the influence of wiring and transistors, increase the light input per pixel, and suppress the problem that the change of light incident intensity leads to the decline of sensitivity by allowing light to irradiate the back of the silicon circuit board. The sensitivity is twice that of the traditional front lighting CMOS image sensor, and low noise is achieved. The advanced shutter effectively improves the sensitivity and reduces noise. It can also take high-definition, smooth and high-quality images in extremely dark scenes at night.