Objects above absolute 0 degrees radiate energy. The lower the temperature, the longer the wavelength. Generally at room temperature, it is infrared. When the temperature is about 800 degrees, the radiation is visible light, which is why the iron burns red and you can see bright light. We cannot see infrared rays. At night, there is no visible light, but infrared rays are still radiated. The temperature of people and surrounding trees is different, and the wavelengths of infrared rays radiated are also different. The principle of infrared night vision is to convert infrared light that we cannot see with the naked eye into visible light. Because the radiated infrared rays are weak, the converted visible light is also weak. The image is green because our eyes are most sensitive to green light and get tired easily, which makes us see better in low light. Moreover, the difference between red light and green light is that the wavelength is different, and it is easy to change. Blurred image at night → photocathode (converts photons into electrons) → microchannel plate (high voltage increases the number of electrons) → phosphor screen (electrons hit a screen with a phosphor coating) So what the infrared night vision device sees mostly green.