Why are night vision devices sensitive to strong light?
There are various types of night vision devices, but they are mainly composed of optical systems, image tubes or micro tubes, power supplies, and power supply systems. Of course, active infrared night vision devices also need to be equipped with infrared searchlights, of which the image tube or micro light tube is the "heart" of the night vision device. The image tube can transform invisible infrared images into visible images, while the micro light tube can enhance weak light by tens of thousands or even tens of thousands of times, making it perceptible to the human eye.
Night vision devices are afraid of strong light because the image tube and low light tube are afraid of strong light. Taking the image converter as an example, when infrared light is irradiated onto the photocathode of the image converter, the photocathode emits electrons, which are accelerated towards the fluorescent screen under the action of a high voltage field (16-21 kV) and an electron lens, causing the fluorescent screen to display a visible target image. The more light signals received by the image tube, the more electrons are emitted, and the stronger the light signal emitted by the fluorescent screen, the brighter the image seen. They are basically proportional. But if the external light is too strong, the number of electrons emitted by the photocathode will not increase to a certain extent, resulting in saturation and making it difficult to see the target clearly. If too strong light suddenly comes in, it may also burn out the photocathode of the tube, making it unable to emit electrons, and of course, nothing can be seen.
Although night vision devices have taken certain measures to prevent strong light, their effectiveness is limited, so they must be operated strictly according to regulations when used. When encountering strong light or daytime calibration targets, wear the objective lens cover or turn off the power switch. Proper use of night vision devices can extend their lifespan and avoid unnecessary damage, thus fully utilizing their potential.
